Notes on Avocado Pollination
by Laurie Meadows
phase avocado flower. The female parts of the flower are obscured by
upright inner whorl of stamens. In this photograph, the white bulbous
anthers at the top of the stamen filaments have not yet shed pollen.
Only the stigmatic surface - at the very top of the style - can be
seen. Notice that one stigma is white and receptive, and the other
brown and unreceptive.
The style, and ovary at the base of the style, are obscured by the
upright innermost stamens.
The yellow staminodes function as nectar secreting organs, and there is
also a true nectary at the base of each of the 3 inner stamens.
Both the petals and the 'tepals' in the avocado are almost identical in
size, shape and color. The tepal is the equivalent of the sepal in a
flower. Sepals are usually small relative to the petals, and a
different shape and color (green, usually). When the sepal is nearly
identical in form and color to the petal - as it is in avocado - it is
termed a 'tepal'.
Modified from Wikipedia image
of avocado cultivar 'Sharwil' anthers shedding pollen. The 'tear tabs'
(valves) on the side of the anthers have peeled upward, releasing the
pollen. The pollen is moist at first and remains in a clump. It soon
dries enough to disperse, but some pollen grains
remain loosely attached to the underside of the
valves (just visible in the photo).
There are 4 valves on each anther, but not all valves necessarily
open, or open
Hass is in a class of its own. It sets fruit when other cultivars
either don't set (edranol), or set erratically (Pinkerton).
What makes Hass so reliable?
The basics of avocado sex
Each flowering panicle has a large number of flower buds. Every day new
flowers open, and two-day-old flowers are shed.
On its first ever opening, the flower opens as a female; all 9 male
stamens do not shed pollen, and lay down flat and tight against the
green tepals, leaving the the female ovary, style and stigma totally
exposed. The stigma is white and receptive to pollen. After some hours,
the flower closes.
The flower remains closed until the following day, when it opens again
in the pollen shedding 'male' phase, although the female parts might
still be receptive. If the stigmatic surface has turned brown and
somewhat shriveled, it is considered unreceptive to pollen. After some
time, the flower closes for the second, and last, time. It it hasn't
successfully been fertilized, it withers and falls off. If it has been
fertilized, it begins to form a fruit.
The flowers synchronize their sex phases - the tree slow motion
switches from all flowers on the tree female flowers only, to all
flowers on the tree closed, to male flowers only, to all flowers closed
and so on. But the neat time-of-day synchronization of floral gender only
happens in consistently warm temperatures.
In New Zealand, there is often overlap between the genders. Some
flowers are late to finish their cycle, and some flowers of the
opposite gender-phase open before the last gender flowers of
the previous gender-phase have all closed. In the main flowering period
(when it is warmer), the Hass female flowers open around about midday.
If it has been cool for some days, female flowers might not open until
the late afternoon. (Recent research in New Zealand has shown that
periods below 7oC push Hass female flower opening later and later in
the afternoon, and then into the night.) Conversely, if it has been
very warm for a few days, female flowers might even open in the morning
and close at midday (as it does in hotter countries). The flower's
female phase ends when the flower closes 1 or 2 hours after opening.
The same flower re-opens the next day, but as a male, shedding pollen.
The Hass flowers male phase (pollen shedding phase) typically starts
when the flower opens in the afternoon or evening. The flowers stay
open all night, and are finally exhausted by late the next morning.
Sometimes the male phase flowers open early, about mid morning.
Either sex-phase of the flower can vary greatly in opening
and closing time on any given day.
Indeed, I have noticed that early in the season, sometimes
morning sunshine on the eastern side of some trees seems to
promote flower opening on that side, whereas the flowers on the
southern and/or western side (shaded from the morning sun) remain
closed. Interestingly, researchers in New Zealand have noticed the
opposite phenomenon, albeit with much larger trees. Either way,
variation in the timing of flower opening 'within-tree'
might possibly be useful in allowing overlap of the sex phases.
The variation in opening and closing
times of the two flower phases is not particularly important. What is
(somewhat) important is that there is often a little bit of overlap
between the end of one flower gender phase, and the start of the other
That said, in New Zealand's humid conditions it may well be that the male
phase flower may still have viable female parts when it opens, and may
be able to set by itself, given a little assistance from pollinating
insects (or even gravity). There is mounting evidence that the male
phase flower is the one that sets the bulk of the crop (contrary to
what was thought).
But for physiological reasons, the avocado
flowers simply won't set until it is warm enough for long
enough. And once it is warm enough, set of the main summer and autumn
cultivars (Hass and Reed) is virtually assured.
The bottom line
Whatever the intricacies of flower pattern, in New Zealand at least, Hass
sets well in the backyard without any need for pollen from a different
cultivar, as does does the late-setting Reed variety. The 'up and
coming' Hass-like green-skinned 'Gwen' variety also has a reputation
for similar easy reliability. As long as only these varieties
are planted, they will set fruit.
But Hass and Reed varieties are more or less summer and autumn
varieties (respectively). Hass fruits can be (selectively) harvested
early, from around september, and Hass continues to fruit until
january, at least. Hass trees in cooler parts of a garden might flower
later, and hold their fruit on the tree as late as may. Reed is ripe
late summer and autumn. So the 'gap' in fruit production is june, july,
and august. (The winter varieties 'Bacon' and 'Zutano' ripen in about
july to august, but their flavor is very poor, so we can ignore them).
The only reason to even think about pollination is if you are
trying to establish good quality varieties that might fruit in winter.
If you are happy with summer and autumn fruit, then read no further!
Winter fruiting good-quality Avocados
The only good-quality avocado varieties available that are 'supposed'
to fruit in winter are Fuerte, Pinkerton, and, to an extent, Hashimoto.
Fuerte, like Pinkerton, flowers over a very long time, from
early winter to late spring. In a warm spring its early flowers may set
fruit, which are good quality by about july.
In a 'normal' year (north of Auckland, at least) its flowers won't set anything
until about october, the same as Hass. Fuerte will produce female
flowers at lower temperatures than most other 'B' types, but needs warm
days (best at 25oC or over) to set seed and hold the fruit.
Fuerte fruit set in a normal year aren't good quality until about
august. Even then, once picked, they can take 9 to 14 days to ripen on
the kitchen bench, so the fruit is not ready to eat until late
august/early september. Normal season fruit size-picked in july usually
taste like soap.
Fuerte fruit set is erratic from year to year, depending on
winter/early spring temperatures.
Pinkerton has about the same flowering period as Fuerte (maybe
slightly later). In San Diego USA it is called 'winter Hass', because
its earliest crop is in mid winter. My experience (so far) is that
flowers will not set until mid october - once again, the same as Hass.
The fruit from this set matures about september, but can be picked as
early as late July. The fruit are oily and very good, but don't have
the depth of flavor that Fuerte has. They are better than early picked
Hass. I assume that in unusually warm years it will set earlier, and be
harvestable in august, like Fuerte. My experience is that this variety
sets very poorly unless it has a suitable pollinator.
Hashimoto matures fruit from roughly april to july. I suspect
that it is like Reed, a late spring flowering tree whose fruit take 18
months to mature. I am guessing the fruit hold on the tree into the
early winter months. The trees here were only planted in spring 2012,
so it will be a few years before I find out. (Late set Reed fruit will
also hold into july, but late flowers in any given year can't be
Although Hashimoto is a 'B' type, it reportedly fruits well, at least
in the Bay of Plenty. Presumably it sets well on its own pollen. If
Hashimoto holds on the tree into winter, then it may turn out to be the
best choice for a good-quality winter fruiting avocado. The ability to
pick fruit in late autumn would be a bonus. Hashimoto fruit have very
good oil content, albeit the flesh can seem a little dry, not as
'smooth' as Hass. It also has obvious brown fibers in the flesh, but
these are not noticeable when eating the fruit. It has a thick skin,
like many of the large round Guatemalan avocados, making a little hard
to tell when the fruit has ripened. In the hot conditions of
California, it has a reputation for going 'bacony' and 'off' if left on
the tree too long. I doubt that will be a problem in our cooler climate.
Barriers to fruit set
The most important barrier is the flowers dependence on warm
temperatures to set fruit.
The avocado is a subtropical fruit. Its natural habitat in the
subtropics does extend up the side of mountains, into cooler climate
zones. But there are limits. Its foliage is frost sensitive, and trees
can be killed by severe freezes. If the tree allows flowers to set at
cold times of year, then it has more chance of a night, or nights, cold
enough to freeze the developing fruit and kill it. The investment in
initial fruit growth would then be lost. So the tree behaves as if it
has a 'built-in thermostat' that stops flowers from setting when the
general air temperature is relatively low. The tree may flower in
low temperatures, but it drops them all, even if the flower is
Flowers of a number of 'B' types (e.g. Sharwil) will not overlap
their own male and female flowers well unless temperatures are at least
25oC by day and at least 20oC at night (Whiley 1987). This is
irrelevant for New Zealand because 'A types' such as Hass are available
to act as pollinators. More to the point, while some 'B' types produce
prodigious numbers of male flowers (for example Sharwil and Fuerte),
they may produce very few female flowers anyway. (Some 'B' type
varieties such as Edranol seem to have an additional temperature
mechanism - the female phase simply doesn't open if the temperatures
are not high enough for long enough. And in this part of New Zealand,
they evidently are not!)
Flowers of 'A' type avocados are most
likely to set from self pollination (i.e. there is at least some
overlap between male and female phasing) when day temperatures are
between 23°C and 27°C, and when night temperatures are 10°C or higher.
Natural daily variation above or below these temperatures can also help
Young fruit are retained only when air temperatures are
warm enough for long enough. Research suggests a minimum night
temperature over 15.5oC, and a daily maximum of at least 21oC. These
minimum temperatures probably need to continue for at least 2
consecutive days. The 15.5oC night temperature is almost certainly
incorrect under our conditions, as such high night-time temperatures
are not often reached in spring (when fruit set) in New Zealand. Recent
research shows a combination of high relative humidity and temperatures
over 20oC are needed for maximum pollination adhesion to the stigmatic
surface and maximum pollen germination.
(Conversely, when temperatures exceed 25oC, pollen
germination decreases in the male stage flower, probably due to the
female stigma drying out - but if relative humidity is high, the
stigmatic surface remains receptive, and pollen germination remains
high, even at these higher temperatures.)
Pollen takes between between 24 and 48 hours to grow down the female
flowers stigma, reach the ovary, and fertilise the ovule. Cool
conditions slow the growth of the pollen tube. If it is too cold, the
pollen tube stops its journey altogether. But there's a deadline. If
the ovule isn't fertilised within 48 hours, ethylene is
produced at the base of the ovary, and this cause the ovule to abort
and the flower to drop off.
In addition, there is some evidence that the ovule itself does not
mature properly in cool weather. In this case, even if the pollen tube
reached the ovule in time, no embryo would form.
Temperature seems to be the primary determinant of when avocado
panicles will start to set and hold fruit under our climatic
conditions. The avocados here either don't set at all, or don't hold
the 'apparently set' fruitlets until extended periods of warmer
conditions arrive - usually in very late october and early november.
Every other factor - pollinating insects, overlapping male and female
floral stages, cross pollenizing varieties - appears to be secondary to
prolonged periods of warmer weather.
Male and female flower parts receptivity
Overlap between the separate male and female flowering phases
Here in Helensville, at least, different Pinkerton trees can be 'out of
synch' with each other by an hour or so, resulting in a slight overlap
of male flower phase and female flower phase between different
trees. The trees are at some distance from each other, so pollen is not
likely to be carried to the female phase tree. Nevertheless, small
differences in timing do exist between trees, perhaps reflecting
different micro-climates, or even different rootstock effect.
The earliest flowers of one sex-phase's floral opening often
overlap with the last flowers to close of the previous sex
phase. Again, the result is overlap of male and female flowers, but
this time within the same tree.
A small amount of overlap between phases is fairly common in our
climatic conditions. Under cool conditions the time of opening of
female flowers is delayed. Here in Helensville, flowering at the
warmest part of year is fairly synchronous, with relatively little
overlap, but if there are unusually cool nights or days, opening and
closing phases shift all over the place. Indeed, the 'A' pattern can
temporarily become the 'B' pattern.
It is ironic that the cool weather in the early part of the avocado
flowering season causes the greatest overlap in the female and
male flowering phases (sometimes up to 4 hours), but the same low
temperatures mean that fruit are most unlikely to set!
Overlap between male and female parts within the same flower
Florida research showed that after the female phase flower closes, very
often the female stigma remains white and receptive the next day, when
the flower re-opens as a functioning male. In fact, their data showed
that anything from 25% to 85% of male phase flowers are successfully
fertilised (lower in dry conditions, higher in moist, humid
The success of flowers self or cross fertilising in the male phase is
perhaps supported by the fact that Israeli research showed that Hass
male phase flowers have over twice the amount of sugar that
female phase flowers have.
A lot of the information on avocado pollination comes from California
and Israel. These are Mediterranean climates, with much less relative
humidity in spring. San Diego, for example, averages about 60% to 70%
relative humidity - low by our standards - even although it is in the
supposedly 'humid' coastal zone (Chilean conditions are very similar -
dry, with low rainfall). And both California and Israel can have 'mini
heat waves' when temperatures skyrocket, even in spring. Under these
conditions, it is much more likely that the female stigma and style on
the male phase flower will have dried out, making male-flower
pollination less likely. No wonder they focus on the importance of 'B'
type varieties as a pollen source for the commercially important 'A'
type Hass variety.
Recent (2001) research in California has shown that the Florida
situation is operative in California. Whether bees were present or
not, only about 3% of available stage 1 female flowers received
1 or more pollen grains (there was no overlap of male and female phases
at the time of this study, so the pollen likely came from nearby Zutano
And again, whether bees were present or not,
around 18% of the open stage 2 male phase flowers had 1 or more pollen
grains on the stigma. This pollen was from the trees own flowers (or
from adjacent Hass trees). In the more humid coastal areas, over 95% of
the male phase flowers had receptive white stigma during the 2001
flowering season (hotter inland areas only had around 50% receptive
stigmas in the male phase).
Although a relatively low number of the total avocado flowers open ever
received any pollen at all (~ 3% in the first opening and ~ 18
% in the second opening), it means that even in California, about 80%
to 85% of Hass flowers actually pollinated were from self-pollination
in the male phase flowers.
For New Zealand, with its roughly 90% relative humidity in
springtime, the female structures in the male phase flower are probably
in excellent condition to receive pollen from the immediately adjacent
anthers - as is the case in humid and semi tropical Southern Florida
and in Coastal California.
Of course, planting other varieties nearby does allow cross
pollination between varieties. The 2001 Californian work showed that in
the absence of overlap between the two gender phases, wind borne pollen
from other adjacent varieties would contribute 15% more flowers with
one or more pollen grains to the stigma. That does not
translate to a 15% increase in total crop (by weight) however!
For a start, South Florida researchers showed that pollen
from other varieties did not set more fruit than a
varieties own pollen. Isozyme
analysis of the set fruit of 3 different cultivars showed that over 85%
of the harvested fruit were from self pollination. In
other words, a given varieties own pollen is usually as 'potent' as
that of another unrelated variety.
It had previously been shown that Hass seemed to
preferentially retain fruit that had resulted from out-crossing with
another variety. However, it has since been shown that the fruit set
right at the end of the flowering period are the ones most likely to
drop (due to competition for resources from the flush of new vegetative
growth and the rapidly growing earlier-set fruit). Late set fruit are
formed when the main cross pollinator varieties have finished
flowering, so late set fruit are all self fertilized. This was
interpreted as a general disposition of self fertilized fruit to drop,
and out-crossed fruit to hang on.
Further work has demonstrated that in humid climates there is
no significant difference in ultimate crop weight between Hass orchards
with pollenizing varieties nearby, and orchards with no pollenizing
trees at all. (However, Pinkerton, specifically, is an exception to
this rule.) In contrast, in arid Mediterranean climates with dry air
(Chile, large parts of inland California), 'B' varieties for cross
pollination are essential.
If it is the case in New Zealand that the male flowering stage is the
stage most likely to set fruit - as seems likely - then there are only
two other possible barriers to within flower
pollination worth noting: lack of insects to transfer pollen from
anther to stigma (a distance of only millimetres); or some physical
barrier to a flower pollinating itself in the male flower stage.
A further twist to the tale of avocado flower set was the discovery by
Spanish researchers that the avocado flowers that hold on the tree and
form fruit are disproportionately those flowers with high starch
levels. But only a few of the thousands of flowers on a tree
have very high starch levels. The researchers showed that whether a
Hass tree is in a heavy cropping 'on' year or a low cropping 'off'
year, the proportion of flowers in a raceme that go on to form
and hold a fruit are the same. The 'on' year fruit are more numerous only
because the sheer number of flowers is much higher in that year.
Flowers, fruit, roots and leaves compete for resources
Hass tends to have heavy crops one year and light crops the next. A
heavy crop on the tree is still maturing its fruit in spring, just as
the flower panicles are demanding stored resources to expand and
produce their innumerable flowers. New leaf growth starts pushing
through the flower panicles at the same time. And it is said that root
growth more or less coincides with shoot growth. So there is a very
heavy call on the trees stored resources in spring, just after a long
period of unfavorable wet and cool conditions in winter.
You could argue that a tree with a heavy load of fruit to ripen 'self
regulates' by devoting more stored resources to ripening its existing
near-mature fruit than to producing lots of flowers for next years
'possible' crop. And it is a forest tree, so if it is to successfully
compete for light, it has to extend growth every year, no matter what
the fruit load. So any one years flowering is, to a degree, expendable
for the long-term greater good of the tree.
Physical barriers to pollination
The male flower stage is illustrated in the photo at the top of the
page. One characteristic is that the innermost group of 3 stamens stand
tight and vertical against the style. In most avocado cultivars the tip
of the style, bearing the receptive stigmatic surface, extends slightly
higher than the enclosing inner stamens, and so is still exposed to
pollen. Pinkerton has a long style with a distinctive 'kink' in it.
Perhaps it is bent because it is so long. Whether this delays the
transit of Guatemalan race pollen to the ovule (it is claimed to set
heavily in the presence of Mexican race pollenizers) or not is
speculation, but could be considered as an explanation for Pinkerton's
reluctance to set fruit. Pinkerton is a seedling of the variety Rincon,
and Rincon is sometimes considered self-infertile. Possibly it suffers
from the same physical barrier.
The female stage flower has no problem receiving pollen because all the
male stamens are 'out of the way', laying down flat, totally exposing
the the style and stigma. But in the female stage, no pollen is shed
from it's horizontal male parts. So if Pinkerton is
physiologically self infertile, or if the male phase flowers
have 'weak' pollen that takes too long to grow down the long style,
then Pinkerton is almost obliged to have another variety
nearby that is shedding pollen when Pinkerton is in its female stage.
And as a result, Pinkerton is very reliant on insects moving to it from
an adjacent pollen bearing tree.
Wind pollen transfer
South Florida research suggests that in humid conditions wind and
gravity are effective agents of pollen transfer.
Indeed, in Southern
Florida, shaking branches at the time of pollen shed increased fruit
set and retention over unshaken branches!
Researchers further showed that the moist pollen clumps dried out
within 30 minutes or so, and were soon dispersed by insects, wind, or
gravity. The amount of pollen in the air in the tree is not really
important - it is the amount of pollen that blows the few millimetres
to the female stigmatic surface of the same (male phase) flower. An
avocado flower needs 20 grains of pollen on the stigma to be able to
complete fertilization (even although only 1 grain ultimately makes it
into the ovule to form the embryo).
No research has been carried out in New Zealand into the effectiveness
or otherwise of within-flower wind or gravity assisted 'self'
pollination. So that leaves insect pollination.
Insect pollen transfer
Once again, under low relative humidity Israeli and Californian
conditions, it has been shown that almost no fruit set if
pollen-transferring insects are excluded from the tree. And when a
beehive is included, fruit set normally. But these facts may reflect
the dependence on flower stage (female stage vs male stage) overlap,
where, under Mediterranean climatic conditions, only female
stage flowers can set fruit, as the later male stage flowers have
dried-out female parts (due to the low humidity). The male stage, under
these conditions, can only act as potential pollen donors, given they
'hang on' long enough to overlap the earliest flowers of the next
tranche of female flowers to open.
Under New Zealand conditions, flowers may set fruit at the second
floral opening from pollen released immediately adjacent to the
still-functional female stigma. This process may be enhanced, or
overtaken, by insects knocking pollen onto the stigmatic surface.
In its native habitat in Guatemala and Mexico, avocados are said to be
pollinated by stingless bees.
My experience here at
Helensville can be summarized as follows:
1. In general, there are either relatively few or no larger insects on
the flowers at any given time, except;
2. When the male phase flowers are producing nectar there will
almost always be 1 to 6 larger insects on the flowers
3. There are more insects on the flowers when it is a consistently warm
4. There are more insects on the flowers later in the season when the
weather is warmer and the days longer
5. Some varieties clearly produce more nectar than others, and are
therefore more attractive to insects than others.
6. Set seems to happen in late october, very early november, even when
in some trees there are few flowers remaining on the panicles (relative
to early and mid october)
by pollination effectiveness (taking into account the number of pollen
grains deposited on stigmas, the frequency of stigmatic contact, the
number of flowers visited per minute and the number of individual of a
species around at any point of time per number of open flowers at that
research by Rader et al (2012) on pollination of a brassica field crop
in the South Island indicates that the natural diverse wild pollinator
insect population pollinates the crop about as effectively as managed
hives of bees.
Most of the pollination was done by 8 species of insects. The 'number
one' pollinator was the honey bee, second in importance was the
bumblebee, third was the drone fly (Eristalis tenax),
fourth was a native bee, Leioproctus sp., fifth was the hover
fly Melangyna novae-zelandiae, sixth the blossom fly (also
called the March fly or St. Mark's fly) Dilophus nigrostigma,
seventh was the hover fly Melanostoma fasciatum, and eighth was
another native bee, Lasioglossum sordidum.
Results from an annual crop grown in a different geographic and
climatic region are not necessarily comparable, but the effectiveness
of the various pollinating insects is perhaps indicative (even
considering the differences between brassica and avocado pollen).
The effectiveness of the honeybee and the bumblebee are not surprising
- both work when avocados are flowering in late september, and october
to november. Both touch the stigmatic surface of almost every female
flower they visit, both carry greater than the minimum 20 grains of
pollen needed to effect pollination. What is a little surprising is
that the drone fly just about matches the top 2, in these attributes;
it is just not as abundant. Bumblebee numbers peak in mid spring to
early summer - exactly in the main flowering period.
The drone fly is attracted to yellow and green flowers - which happens
to match the avocado flower color tone. Male drone fly numbers peak in
summer, and female in winter (Irvin et al. 1999). Summer is a little
late, and winter is a little early!
The Brassica crops fourth most effective pollinator, Leioproctus
sp does not appear in Helensville until avocado flowering is all but
over (in Hass, at least). The blossom fly also doesn't appear in
numbers until the flowering is all but done. That leaves the hover
Melanostoma fasciatum is abundant
here, and while it is low on the ranking of the 'top 8', it does appear
as the avocado blossom season starts.
The Blossom fly, a Tachinid fly ('bristle fly') is said to have its
peak of activity in november and February (Harrison 1990), a time of
peak insect activity and peak species diversity. It has been recorded
by New Zealand researchers on avocado flowers, with avocado pollen
observable. The pollen load is on the underside or the body, most
likely to contact the stigma, and the amount is considerable - almost
as much as bees (Rader et al. 2009).
Many flowers have a resident population of thrips. They are active
little insects, and I have seen them climb all over the shedding
anthers, across the stigmatic
surface, down to the
base of the flower, and back again. Whether they knock the required 20
grains of pollen onto the stigma, or whether they can carry a decent
load of pollen on the underside of their bodies, I don't know.
Avocado flowers often have 2 or 7 ants crawling around the base of the
flowers when the nectaries are producing sugar. The ants tend to remain
at the base of the flower, but even so, may knock the pollen from the
inner anther whorl onto the female stigma. Their bodies lack much in
the way of hairs that might trap pollen. I have looked at a couple of
ants close up, and they only have 3 or 4 pollen grains on them, usually
on their legs. One ant had a single grain on its head. So while they
might help distribute pollen within the flower, the chances of
transferring pollen between flowers seems pretty small. Ants are
known to secrete an antibiotic which kills pollen, so they are
unhelpful in pollen transfer between flowers.
Miscellaneous beetle, weevils, and other random insects
time to time avocado flowers are visited by an eclectic mix of insects,
from beetles to weevils. I have no idea what they are. One visitor, a
small metallic grey-green beetle, had a few pollen grains stuck to the
underside of its body, but nothing on its rather hairy legs. Its
excreta was largely pollen 'shells', which are excreted after the
nutritious contents have been enzymatically extracted.
The steel blue
ladybird, Halmus chalbeus, is fairly frequently seen on avocado
flowers, and I have watched it eat pollen. It, too, may accidentally
knock pollen onto the receptive female stigma, but is unlikely to be
hairy enough to transport pollen between flowers.
In late april 2013 I observed a fungus-eating ladybird, Illeis
galbula, 'nose down' in an ultra-early Pinkerton flower. It was in
the female phase, so no pollen was available. Observation with a
hand-lens as it moved about the panicle suggested it was as likely
eating the very fine hairs on the avocado, or perhaps detritus trapped
on the hairs. Again, an unlikely pollinator.
Adult click beetles sometimes feed on nectar in late spring.
I have seen the odd flower longhorn beetle (Zorion
sp.) amongst the flowers on the odd occasion, but only as a relatively
rare sighting (photo left - also, note the open valves on the anthers)
. There is a claim that a "high majority" of the fruit set in a
particular western Bay of Plenty organic orchard is "facilitated" by
these native beetles. This beetle was first observed at that orchard in
october, so the timing for pollination is right. A team from Plant and
Food Research is cataloguing the pollinating insects (other than honey
bee) on this orchard, and how much avocado pollen they carry. The
results, when ultimately published, will be interesting.
The drone fly, Eristalis
tenax, turns up from time to time fairly early in the flowering
season. This insect looks for all the world like a bee, but isn't. It
has a hairy body, and can transfer as much, or more, pollen as a bee.
Sturgis McKeever, Georgia Southern University, Bugwood.org
Other, smaller flies commonly visit avocado flowers in spring,
especially in sunny weather. Flies typically wander all about adjacent
flowers in between nectar feeding and they have hairy bodies,
so they may be useful agents for pollen transfer. Blowflies are common
in late september when the weather has warmed, but while they visit
flowers, the visits are relatively infrequent, and most of their time
is spent basking in the sun on the mulch at the base of the trees.
The only fly I have seen on the autumn flowers (so far) is
the Australian leafroller Tachinid (Trigonospila brevifacies).
This stripy little fly lays an egg on leafroller caterpillars, and when
the maggot hatches it eats the caterpillar. The avocados have never
been sprayed, so the trees do get leafroller, but not that many.
Perhaps the fly is the reason why. Anyway, the fly observed fed
diligently at the nectary of the flower it was on for some time
Around 10 species of solitary bees are one of the primary pollinating
insects in the humid subtropical forest that is the native habitat of
New Zealand has several species of native solitary bee, but they are
not active until early summer, by which time most avocado flowering is
over. Around about
the 1st of december 2012 I observed both the most common
native bee (Leioproctus
fulvescens), and the second most common native bee (Lasioglossum
sordidum) on very late Hass avocado flowers. A Reed tree, which is
later flowering than Hass, was also attended by L. fulvescens
at this time. While
Lasioglossum sordidum is not very hairy, Leioproctus
fulvescens is. The females of both species carry
pollen in pollen sacs on their hind legs. Leioproctus
fulvescens also accumulates pollen on its hairy
thorax, and, to a lesser extent, on the underside of the thorax. Both
bees nest in holes in the ground, and prefer areas of bare earth. I
suspect these solitary bees may be useful pollinators for late
flowering avocado cultivars, such as Reed and Fujikawa, but there is no
evidence either way.
The native bees of the Guatemalan and Mexican subtropics that pollinate
avocado are adapted to the humid climate there. When a similar species
was introduced to Israeli avocado orchards to improve pollination, the
colonies quickly died out due to periods of intense dry heat. So the
domesticated colony-forming bee, Apis mellifera, is the most
common substitute we have for the native pollinator.
Here in Helensville, bees visit avocado flowers more frequently than
any other insect, with the exception of the bumblebee, Bombus
sp., the German wasp, Vespula germanica, and possibly the
Australian paper wasp, Polistes humilis. But there is a big
qualifier: not in cold weather.
Bees 'pack it in' when there is a run of cool weather (once
temperatures drop below 12oC, and sun radiant energy falls below 300
watts per square metre - 800 watts/M2 is a bright cloudless
day). Even so, I am not infrequently surprised at the odd intrepid bee
visitor out and about in gusty or overcast conditions. Bees are good
pollinators because they are more diligent than many other insects,
they tend to go from flower to flower methodically, rather than
spending time flying from one area of the tree to another. Like flies,
they tend to clamber over adjacent flowers, and could easily knock
pollen onto the stigma, as well as brush the stigma with pollen laden
body hairs. Israeli researchers found that a bees head will almost
always have to push against the inner whorl of anthers when it is
collecting nectar. Not only does this make dislodging pollen more
likely, but the pollen tends to collect in clumps just between the
antennae on the bees head, ideally positioned to transfer to other
Nectar collecting bees visiting flowers
that are shedding pollen
usually carry large
amounts of pollen on their bodies - several thousand grains. But, (for
the Hass variety) there are only an average of 25 pollen grains on the
hairy underside of bees visiting the tree at a time when it is doing
its female phase flowering. This points once again to the possible
importance of the male phase flowers, in that bees moving
between and within them are carrying a very large pollen load, so if
the female stigma is still receptive in the second-day flower, it is
almost certain to receive pollen. But the female flower will be
visited by bees carrying very little pollen - unless there is a little
overlap between the close of the male phase and opening of the female
phase; or unless an 'opposite phase' avocado is flowering close by.
Nectar collecting bees don't collect pollen. Israeli researchers
observe that after about every 4th flower visited, the nectar
collecting bee very efficiently combs out the pollen while hanging from
a leaf, or hovers and dumps it in mid air. A mid-air pollen dump causes
a small cloud of thousands of pollen grains to disperse.
Bees are not always good pollinators; some bees can detect the
freshly produced nectar in male flower buds that are just at the point
of opening, and are adept at forcing the petal tips open far enough to
suck up the sweet sugar while the bud is still closed. In this case,
contact with pollen doesn't happen. It is an open question as to
whether pollen masses are knocked onto the immediately adjacent stigma.
I say this because the terminal and sub terminal buds of the avocado
panicle are the largest and most mature, are probably are secreting the
largest amounts of nectar, and possibly for that reason are favored by
bees. My impression is that most avocado set is from these terminal and
Bumblebees are a regular visitor
to avocado flowers here. They don't always stay long, but if the nectar
is flowing, there can be 2 or 3 on the same tree, and they spend quite
some time collecting. Bumblebees have the ability to regulate their own
body temperature, and can be the only insect working the flowers early
on a cool morning, or late evening. On cool, windy, overcast days, when
bees are almost absent, it can still be found at work on avocado
flowers. The commonest species is Bombus terristris, and in
Israel this species was noted as working faster than honeybees,
visiting 20 flowers per minute against the honeybees 6 to 9 flowers.
Israeli researchers found bumblebees were much less likely to
concentrate solely on cultivars such as Ettinger which have high
amounts of sugar. Bumblebees visited less attractive low sugar
cultivars such as Pinkerton almost as frequently as the more rewarding
Bumblebees take some time to build up their new colony in spring. The
colony starts with a single queen, and ultimately builds to maybe 200
or so workers. The small worker bumblebees appear around early to mid
october here. Bee colonies, on the other hand, can, at full strength,
have more than 50,000 workers - which makes them very valuable
'instant' full-strength big-number pollinators for commercial avocado
German wasps, Vespula germanica, are also common visitors to
avocado flowers. Like bumblebees, they seem undeterred by cool
temperatures and approaching nightfall. On a sunny day, there can be 4
or more wasps on an avocado cultivar with attractive nectar at the peak
of nectar secretion. I haven't seen any information on the efficiency
of German wasps as agents of pollen transfer. Likely they might knock
the pollen of shedding anthers in the inner whorl onto the stigmatic
surface in male phase flowers, but I doubt they carry much pollen on
Polistes humilis, the
Australian paper wasp, and Polistes chinensis, the Chinese
paper wasp (photo left), both regularly attend avocado flowers, P.
humilis much more than P. chinensis. Again, their
efficiency as pollinators can only be guessed at.
Microscopic examination of Polistes
in Trinidad avocado orchards confirm that P. canadensis, at least, does
carry avocado pollen on its body, but they carried less pollen on their
bodies than bees. Presumably other Polistes are similar.
The Chinese paper wasp seems active earlier in the season, and these
wasps are clearly attracted to avocado racemes even when only small
numbers of flowers are open. They seem to locate honey sources with
their antennae, rather than visually. This leads them to wander all
over the fattest buds of the flowering raceme before they find an open
flower. Sometimes they bite the yet-to-open petals of a very fat bud in
a futile attempt to access the sugars within. When an open flower is
found, they bring their antennae forward and parallel, 'checking the
scent'. If ants are present in the flower (often the case), they will
abandon it, and keep looking for a 'vacant' flower. This wandering, and
aversion to ants, means that they visit relatively few flowers.
In early november 2012, I observed a European potter wasp (Ancistrocerus
gazella) feeding on nectar (not pollen) in a Pinkerton tree.
The drone fly, a type of hover fly, has already been mentioned. While
an effective pollinator, it is not particularly common.
Both the 7-10 mm long 'large hover fly' Melangyna
novae-zealandiae (also called the 'dark hover fly',
and 'the flower fly') and the 'small hover fly,' Melanostoma
fasciatum, visit avocado flowers from time to time.
These 'flower flies' can be told apart by the orientation of their
wings when at rest. The 'small hover fly' lays its wings parallel with
its body; the 'large hover fly' holds them out at a 45 degree angle.
Small hover flies seem more prevalent early in the flowering season,
and are far more numerous than the 'large' hover fly. I have only seen
the Large hover fly fairly late in the flowering season, when most
fruit seems to set.
Again, there is little information on their efficiency as pollinators
(but good information in relation to Brassicas), albeit my observations
in late september 2013 indicate they quickly and accurately locate only
open flowers. Once on a nectar producing flower,
however, they feed for a longer time than most other insects. Given
their relatively small size, it is reasonable to suppose their energy
needs will be relatively easily met, so the number of flowers visited
might be relatively low. Rader et al (2012) found bumblebees visited
about 17 - 55 Brassica flowers per minute, where Melanostoma
fasciatum visited around 2 - 5
flowers per minute. Bumblebees deposited from ~ 50 to 500 Brassica
pollen grains on the stigma. In difference, Melanostoma
deposited about 1 to 14 grains.
Adult hover flies meet their protein needs by eating pollen of grasses,
plantain, sow thistle, Phacelia, and certain
other flowering plants. 'Small' hover fly larvae eat small
caterpillars (and aphids), so are 'dual purpose' insects around the
The 'Metallic Blue Hover fly' (Helophilus hochstetteri) visits
avocado flowers when it is warm and sunny (its latin name 'Helophilus',
means 'sun loving').
Sometimes a large striped hoverfly feeds on avocado nectar. It is
probably the Threelined Hover Fly (Heliophilus trilineata).
Threelined Hover fly on an avocado leaf, basking and cleaning after
a sweet meal.
Some notes and observations on flowering and insect activity
These are small 'snapshots' of flowering behaviour and
insect activity at various times of the flowering season, and under
various weather conditions. Times after the end of September continue
to be 'real' time, not daylight saving time.
Unless otherwise noted, all temperature records are from a
maximum/minimum thermometer on the south side of a tree, in the shade
of the foliage, and at head height.
January 01, 2012
Our 'newest' Reed tree flowered very well for the first time
this year. It set myriads of tiny fruitlets, be-speaking a good first
time crop. These have now all fallen. Hundreds of them. However, there
are (literally) one or two tail end flowers that appear as if they are
setting into tiny fruitlets. I don't expect them to hold. (April 2012 -
they fell off.)
March 26, 2013
One heavily pruned Hass tree has several branches with 'out of season'
flowers. The weather has been warm to hot (25oC maximum) for some time,
with little rain, so it will be interesting to see if there is a set.
April 03, 2013
Temperatures on one day recently climbed briefly to 28oC. The coldest
it has been at night is 12oC. It was cloudy but warm until middday. The
temperature then was 22oC. The 'out of season' flowers on the Hass are
female phase at midday. Only ants are present. The sun came out soon
after, with temperatures reaching 25oC by 1.00 pm. The flowers are
still in female phase, and well attended by ants, but no other insects
April 10, 2012
The first 'out of season' flower panicles on the Hass are fading a bit,
but some new ones are developing. Days have been sunny, and I have seen
a German wasp working these flowers. Ants were well present earlier,
not so much now. ( august - nothing set.)
The 'out of season' flower
panicle on the Gwen has now opened its first flower. (may 16th - It
didn't set any fruit.)
Pinkerton, which has an extended flowering season, is, on average, in
fat bud. One tree is already extending a few panicles.
April 28, 2013
'Out of season' flower panicles on one Hass appear to have set a
few fruit. Another Hass 10 metres or so away is just flowering. At 1130
hrs it is female stage. No pollinating insects were noted (apart from
ants), but the weather is humid, warm (21oC) and breezy. The Pinkerton
trees are in 'fat bud', but low down on the shady side of one of the
trees there are several fully expanded panicles. One panicle has some
open flowers, which are female phase (at 1130 hrs). A one year old
'Carmen' Hass also has some panicles flowering. Other young Carmen
trees elsewhere on the property are from the same purchase, and were
planted on the same day, but have no flowers as yet.
May 16, 2012
The first flowers have appeared on one of the Pinkerton trees. It is
only one panicle so far. The weather is windy, sometimes briefly sunny
and warm, sometimes rainy and cold. No insects are about.
The branch carrying the first 'out of season' flower panicles on one of
the Hass trees has snapped off in the wind. But other flowers panicles
Conditions are the same as yesterday, but the wind is both a bit less
frequent, and a bit warmer.
At midday the Pinkerton flowers that are open seem at the 'moving
between sexes stage', neither male nor female. Last year Pinkerton was
often 'full on' female around 12.00 pm (standard time) in the
afternoon, remaining female overnight and into the early part of the
morning. In late spring, it was likely to be full female late in the
At 2.30 pm the flowers are in the male phase, and pollen packets are
clearly visible. Not a female is to be seen. However, it is, in theory,
possible for the now 'aged' female stigma to still be receptive, if
conditions are right.
The only other avocado close to flowering at this time is the Hass
doing an 'off season flowering' (Fuerte would be, but it is miles away,
and besides, it has been pruned heavily). Both Hass and Pinkerton are
'A' type flowerers, so there 'shouldn't' be any overlap of Hass's male
flower phase with Pinkerton's female flower phase, and vice versa. But
I wouldn't be surprised if their phasings were slightly out of synch,
and therefore able to cross pollenize to a slight degree.
Pinkertons 'early flower flush' tends to open over an extended time,
which means there are relatively few avocado flowers open on any given
To get an indication of the pollinating insects around at this time of
year (and in this weather), I did a 10 minute observation of the
flowers. I saw one honeybee - supposedly the most important pollinator
for avocados - but all it did was a 'standoffish' survey of a few
panicles, before accelerating off again at warp speed. There was a tiny
'gnat' looking insect in one of the flowers (where it stayed), but the
most promising pollinator was a 'small hover fly'. The hover fly
dutifully and thoroughly visited each panicle, feeding at several
flowers as it went.
There are only a few avocado flowers open at this time, so the question
arises, where does this insect go next? I had sprayed out most of the
weeds in and around the trees, and there were only a few random sow
thistles (Sonchus oleraceus)
in flower. And the bright yellow flowers of the sow thistle was where
the small hover fly was resting. Maybe it would be useful to have sow
thistles flowering within the row in may and june, to attract more
small hover flies.
It has been an unusually warm and wet autumn. Today is the first day of
colder weather. One Pinkerton tree has commenced a light flowering.
There is no sign of flowering on the main row of Pinkertons. Several of
the Carmen Hass trees have had flowers for some weeks now.
May 18, 2012
Conditions are breezy to windy, warmer than the last few days, with the
odd brief shower.
At 11:15 the small hover fly was found back on the same sowthistle
flower as yesterday. Pinkerton is in female phase, but there are no
'residual' male phase flowers around to provide pollen.
It is not the case that conditions are too poor for bees and other
large pollinators. I checked the dentata lavender (Lavandula dentata) plants in the
garden, and I estimate there are 4 bees per square meter. A significant
number of bumblebees were observed, and one wool
carder bee. The wool carder bee seems like a very efficient forager
- as good, if not better than, the honey bees. On the rare occasion the
wool carder bee landed on a flower with a honey bee on it, it would
bundle the honey bee off the flower, but did not pursue it. It ignored
honey bees on adjacent flowers.
The question is whether or not growing dentata lavender adjacent to
Pinkerton would attract pollinators to Pinkerton flowers, or whether
they would attract pollinators away from
the flowers. I have planted a Pinkerton hard up against the lavenders,
so I may be able to answer this question in a couple of years time.
At 12:30 The wind is from the northwest, and it is warm enough that a
cicada has burst (briefly) into song.
The Pinkerton flowers are still in the female phase. There are several
aphid-sized 'gnatty' things on the flower, and one small hover fly. I
stayed for 15 minutes to see who else would turn up. The only large
bodied insect to show up was a honeybee. She did an exemplary job of
visiting every panicle with open flowers, and a few with buds only.
Indeed, she went around the flowers twice, feeding avidly, before
At 2:30 the flowers are still in female phase, and no males are
present. A few flowers are either closed, or on their way to being
closed. The only insect working the flowers is an ant.
May 19th, 2012
Sunny and fairly warm this morning, the wind is in the south west this
afternoon and it is cool to cold.
At 1:00 pm A bee and I arrived at the sole flowering Pinkerton tree at
the same time. It was in female phase, but only half a dozen flowers
were open. The bee searched the tree thoroughly, and after visiting all
the open flowers, it then visited the panicles that were in bud. Here
it selected the biggest bud, often the one near the top of the panicle,
and spent some effort and time forcing its proboscis into the unopen
flower. No chance of pollen transfer there...Does it matter? Probably
not. The flowers selected appears to me to be ones that opened at 2:00
pm. Likely the flower will have produced more nectar by the time it
2:00 pm - only a few flowers fully open, all female. An equal number
are half open half closed, so are either female flowers shutting down,
or male phase flowers getting ready to open. No pollinating insects are
4:00 - only a few
flowers fully open, all female. Everything else is closed. At this
time of day there are
no large bodied pollinating insects anywhere
on the property, even in the best sites. It is cold and
overcast. In contrast,
the avocado flowers have 3 absolutely minute diaphanous-winged
gnatty-things, a random 'mega vinegar fly', an insect that looks like a
vinegar fly (Drosophila) but
probably isn't, and an ant-sized black wasp, probably some tiny
parasitic wasp. Not bad, given the conditions.
June 10 2013
Today it is sunny, warm and still from late morning onward. The
air temperature is only15oC, but it is a lot warmer than that in the
sun. A recently planted very small 'Carmen' Hass (known for winter
flowering and fruiting) has many panicles for a tiny tree, and has had
small numbers of flowers open for several weeks now. There are 10
flowers open at 1330 hours, in the male phase and clearly shedding
pollen. A 3 minute observation clocked up one bee, assiduously visiting
the flowers, including a partially open/closed flower. Ants are also
feeding at he nectaries. I have checked the tree at midday on several
occasions recently, and it is always in male phase and always actively
shedding pollen at around noon. There are always ants feeding in the
nectaries. This is the first time I have noticed a bee visit. Other
days may not have been sunny, but air temperatures would have been
similar. Radiant heat temperature effects may have been much less.
Bees cannot fly continuously at ambient temperatures below 20oC. They
must stop and 'bask' to build up temperatures, especially in the
thoracic region 'powering' the wings. It seems to me that bees won't
travel far when there is little prospect of longish periods of
'flight-powering' direct sunshine. The corollary is that it might be a
good idea to have a beehive close at hand for winter flowering avocados.
June 11 2014
Sunny and warm, temperature at midday is 17oC. Overnights have been
mild due to northeasterly weather. At 1200 3 young Carmen Hass trees
have flowers half way open/closed in the male phase. They are shedding
ample pollen. A young Pinkerton tree around 100 meters away has
commenced its 'main early' flowering and is full-on female at the same
time. The stigmatic surfaces are white and receptive. No insects were
observed on the flowers (apart from the ever present thrips). Numerous
bees and bumblebees are visiting the immediately adjacent dentata
lavender hedge, but none were observed visiting the Pinkerton avocado
tree. There were several tiny (midge sized) flies. One with
wonderfully purple iridescent eyes and an irridescent black body,
offset by improbably cream little halters. One was observed feeding on
nectar, but they are as likely to be basking, raising and lowering
their legs in a mysterious signal system known only to other little
flies, no doubt. Around 3 or 4 Nysius bugs are still present,
and their stylets are clearly active around the staminoides, leaving me
with the impression they are perhaps accessing nectar, rather than
sucking the flowers juices. But they seem rather home-bound animals,
and don't seem to move far from a group of 'home' racemes. Not much of
a pollinator. Carmen Hass might be a key pollinizer for Pinkertons
early flowers - if a pollen transferring insect can be found.
August 3 2013
has not been as cold a winter (so far) as we might expect. The lowest
temperature so far (in july) was 3oC. Equally there were some warm
days, and on one day the temperature reached 18oC. The day started
cloudy, but is now sunny, breezy, and warm. At 11.00 it was 17oC.
The flower buds on the best Hass trees are now starting the early phase
of panicle expansion. Only one of the Pinkerton trees has some panicles
fully expanded and starting flowering. All the rest are about with
Hass. Several of the Carmen Hass continue to flower. One has more
panicles than leaves, it seems to me. This particular plant has been
'splutter' flowering for ages, and I can see it is nearly at the end of
its 'panicles to come'. It is in male phase at 1100, and the flowers
are attended by ants (as always), but there is no other insect activity.
August 13 2017
It has been exceptionally mild and warm the last few days. Even night
temperatures were plus 12oC here. The only avocados flowering are
Sharwill and Fuerte (and various Mexican type seedlings). Sharwill has
barely started. I would be astonished if any fruit set this early in
flowering, in spite of favorable temperatures.
Carmen Hass has more or less finished an early winter flowering, with
nothing set. A few panicles splutter on here and there. But there are
no insects - presumably the honey and pollen reward is too meager
to attract them. But Roldana petasitis, (velvet groundsel), a
plant from Mexico-Central America that is "sparingly naturalising in
the Auckland region" (identification Ewen Cameron, botanist, Auckland
Museum) is flowering heavily, and its honey scented flowers are covered
in bees and (a some flies) in spite of overcast and breezy conditions.
The bees are collecting pollen as well as nectar.
September 3 2013
It has been sunny and still in the morning, and sunny and breezy in the
afternoon. Temperatures in the shade are 15oC. Bees, bumblebees and
Monarch butterflies are active in the early flowering 'Pixie' plum
Literally 2 or 3 Hass flowers are open on one tree. Carmen Hass
continues to have flowers open. Carmen flowers are attended by ants, as
usual. A solitary Pinkerton flower is open, and a bumblebee vigorously
worked it, then searched some of the in-bud panicles for more. The
reward from one flower seems to me disproportionate to the effort it
expended. Dusa, which had a few flowers open about a week ago, now has
no flowers open at all.
I noted a 'small hoverfly' around the property, but not near Carmen
(the only reliable flowering avocado at the moment).
It has a been a warm (18oC +) day, but very windy. At least it is a
northerly. Rain is expected by mid afternoon, and then the weather
turns cooler, with a 14oC maximum predicted over the next few days.
1:00 - All the Pinkerton trees are flowering relatively heavily, and
all flowers are female. A bumblebee is actively working the flowers, in
spite of the wind. There are no pollenizing varieties nearby. All the
flowers on the Hass trees are closed.
2:30 - There are only one or two flowers open on the Hass trees, but
they are all female. The Pinkerton trees have a mix of open and closing
female flowers, and flowers in 'male configuration', but not shedding
any pollen. Rain is starting to set in, and no insects are around,
beyond a few ants in the avocado flowers.
A warm day (18oC at 1400 hrs), sunny, clear, still in the morning, a
slight breeze in the afternoon. Bees and bumblebees are in abundance
after a week of rain and cloud. The lowest night time temperature in
the last few weeks was 6oC. The highest daytime temperature was 22oC.
The only avocados flowering (apart from some seedlings) are Fuerte and
Carmen Hass. A queen wasp and Polistes chinensis was observed
on a Carmen Hass, but no bees. Several steel blue ladybirds were busy
eating pollen. The Fuerte was in male phase at 1400 hours, shedding
pollen. The only flowers open are on the very lowest portion of the
tree. All avocados are heavy with developing buds and panicles. It will
be a big flowering season ahead.
A warm day, but totally overcast,with patches of light rain. The sun
came out about 1545 hrs. The air was totally still, the skies clear and
blue. Warmth soaked the trees.
An early flowering Hass seedling (l'il Hass) is being worked by several
'large hover flies' (Melangyna novaezelandiae), half a dozen
worker German wasps, 2 Bumblebees, 2 Asian wasps (Polistes chinensis),
one bee, one drone fly (Eristalis tenax) and 4 or 5 brown
blowflies (Calliphora stygia).
As usual, the worker German wasps, Bumblebees, and bee are by far the
most active and persistent in their work. The blowflies spend
significant amounts of time just basking in the sun.
At 1600 Carmen Hass and a young Pinkerton with no crop load were both
in full female phase.
By 1615, a storm front was
rolling across the sky, bringing thunder, lightening and splotty warm
rain with it. Would any pollen deposited on stigmas be totally washed
away? I don't know.
A warm day (18oC at 3 pm), but breezy and overcast, and in the
afternoon there were a few spots of splotty rain from time to time.
Northerly. A few days ago we had some cold but clear weather, and night
temperatures dropped to about 5oC.
3:00 - The Hass trees have a smattering of flowers open, all in male
configuration but not shedding pollen. One Hass tree has a very
persistent and thorough bee working the flowers, so clearly they are
producing nectar, as
are the smattering of Ruby (seedling) flowers. The Ruby has a large
bumblebee and a German wasp on it.
In both Hass and Ruby the inner whorl of stamens is upright against the
female style. The females stigma is white, and therefore receptive, but
the male parts are yet to shed. In contrast, Sharwil, in identical male
configuration, is shedding heavily. Dusa has a very good number
of flowers open, and all are female (by 5.30 pm the male flowers were
opening, overlapping the female, but not yet shedding. The little
Carmen is flowering 'hard out', and is in female phase, but attracting
no insects beyond the pervasive ants (ants are in all cultivars open
flowers). By 5.30 pm Carmen's male flowers were opening, but not
This morning it is sunny, breezy, warm to cool, depending on the wind.
It has been cold for the last 2 days, and the overnight temperature the
day before yesterday was 7oC, and last night it dropped to 5oC. I'm
very pleased to see the sun today, and at 1030 it was 16oC.
There are 4 or 5 bumblebees working the lavender and other spring
flowers, along with 1 of each Polistes species, but I can see
only 1 bee. The adjacent Pinkerton is closed, but a 'large hover
fly' sits basking on the largest closed flower bud. All avocado flowers
are closed except for the 2 'B' flowering cultivars Fuerte and Sharwil,
and a very 'Mexican' seedling of (probably) Fuerte x Bacon. All have a
lot of flowers open, all in the male phase, and all shedding heavily.
The only insects observed were numerous ants, and in the Fuerte hybrid,
lots of thrips.Carmen
Hass, while mostly closed, has a smattering of flowers
half-closed, with pollen evident.
This morning it is alternately sunny and somewhat overcast, with
a moderate breeze with calm intervals, warm. The morning was
particularly warm, and the days high was 20oC. The overnight
temperature was 12oC, a lot warmer than recent days.
Ar 1615 hours, I was surprised to find one of the Hass trees (the one
with a tendency to have 'loco' flowering) had quite a number of flowers
open on the east side of the tree. The flowers were fully open, and
some were male and some were female. The classic overlap. There are
very large numbers of ants in the flowers, so numerous the flower looks
yellowish black! Clearly Hass is pumping out the nectar. Ants seem to
fit nicely between the stamens as they move in and out, and rarely
travel up to the anthers, where the pollen packets are. The sky has
clouded over, and there is an intermittent light breeze, so it is still
warm. Conditions seem ideal for fruit to set.
Carmen Hass also has both male and female flowers open. Sharwil and
Fuerte have numerous flowers open, and the abundant shedding pollen is
very obvious. The bearing Pinkertons have a smattering of flowers open,
and a young Pinkerton tree has a very good number open. At 1615,
Pinkerton is full-on female. But none of these trees have any
pollinating insects obvious. In contrast, 2 seedling trees, in halfway
male phase, had several bumblebees and other insects on them. The
difference, one might guess, could be the quantity and concentration of
sugar on offer.
By 1730, the female Pinkerton flowers had closed, and the male stage
was opening. These flowers almost all had brown, non-receptive female
stigmas. The anthers had not yet started shedding. Self pollination is
almost impossible. Many of the male flowers had thrips wandering about.
September 25 2012
Night time temperatures have been around 10o C for the last several
weeks, except for a dip to 2o C and 5o C on two nights. Daytime
temperatures have broadly been between 15oC and 18oC (out of the direct
sun). There have been quite strong equinoctial winds, with mixed cloudy
and sunny periods.
The early flowering Hass trees continue to flower, although flower
numbers are relatively small. Pinkerton continues to flower well.
Pinkerton's female flowers seem to open in the late afternoon at the
moment. Hass can shed pollen from mid morning to late afternoon
(depending on the day!). Female flowers have been found in the morning
on one day, and in the late afternoon on another. Always in small
numbers,or just single flowers.
Pollinating insects are often, but not always around the flowers in
small numbers at the times of my brief visits - the bumblebee is a
stalwart, no matter the weather, there is often a bee or two, almost
always thrips, sometimes a fly or two, and sometimes a Polistes wasp.
The number of wasps visiting seems to have dropped off somewhat. Some
Pinkerton and Hass flowers are heavily visited by ants when the nectar
is flowing, but they seem too far below the stamens to be useful.
September 27th 2013
Dead calm at 0830, overcast, humid, warm,
already 16.5oC. Breezy by 0930, some odd sun moments between low grey
clouds. Overcast. By 1030 there were more sunny breaks, warmer, hitting
23oC in the shade! Humid. Dew on grass. Breezy/windy, with calm
periods, threatening showers. Lots of insects around. At 1245
temperatures are 21oC. Overcast, bit of wind, humid, warm. About 18oC
at 1600, totally overcast.
Warm temperatures, calm weather, and humidity
mean conditions are very good for successful pollination. Hass
started opening a few flowers around 0900, and Pinkerton had a few
flowers open at 0830. All are female. By 1100 there were several Hass
flowers open, and both a Melanostoma and an Asian wasp was seen
evaluating some of the fattest flower buds on one tree. A single bee
visitation was observed on another. By 1245 Pinkerton had a good
smattering of flowers open, all female. There were ants in the flowers,
but that is about all. The small Pinkerton tree planted hard up against
the lavender hedge had open flowers within 40 centimeters or so of
numerous bees working the lavender. None detoured to even investigate
the avocado flowers on offer. In another situation isolated from
competing nectar sources there are 4 Pinkerton trees of about head
height. By 2 pm they were covered in open female flowers, and were
being attended by a
bumblebee, at least 5 bees, and around 4 Asian wasps.
Pinkerton is said to set fruit best when there are 'B' type pollenizer
trees close nearby. The only 'B' pollenizer in the vicinity is a young
'Ettinger' tree, but its racemes are still developing, and it won't
flower for at least some days yet. In contrast, a Sharwil tree in a tub
and a branch of Sharwil in-grafted into the small Pinkerton by the
lavender hedge have both had male flowers open in very good numbers
since 0830 in the morning. However, they didn't start to shed pollen
until some time after midday. By 2 pm every flower was shedding pollen.
And almost every flower was attended by ants.
By far the most promising pollenizer for this early time in the main
flowering season seems to be Dusa. It had quite good numbers of flowers
open at 0830, all male, and all shedding pollen. The numbers of flowers
both open and shedding increased quickly, and pollen was shed all day
until 2 pm when female flowers stated to open. The male flowers were
well closing down by 4 pm, but even then the anthers in the semi closed
flowers were still shedding pollen. At 1100 a bee was persistently
working the Dusa flowers, as was a Melanostoma. The bee drifted
down to the in-grafted Hass portion of the tree and actively worked its
flowers. Like Sharwil, the Dusa racemes have a noticeable odour.
The only other possible pollenizer variety here is Edranol, but it had
very few flowers open, and none shed any pollen until the early
afternoon - and even then, only one or two flowers had pollen available.
September 27th 2017
An overcast, humid morning yielded to a slightly windy, but warm,
sunny, humid day.
At 1030 it was 19oC in the shade. Pinkerton had quite a good number of
female flowers open, and Gwen had a few flowers open. Fuerte and
Sharwil had high numbers of male flowers open and shedding pollen,
Edranol only a few. Hass and Maluma remain closed. Insects of all types
abound - German wasp queens, Polistes, flies, bees, small hover
flies, drone flies, ladybirds, thrips, miscellaneous bugs large and
By 1330 both Hass and Maluma were open in female phase, and Fuerte,
Sharwil and Edranol were shedding pollen.
At 1900 hours one Hass tree still has numerous female flowers open.
Pinkerton and Gwen still have the odd female flower open (Pinkerton
more than Gwen). Both Hass and Pinkerton also have good numbers of male
configured flowers, but are not shedding. Fuerte is still male
flowering like crazy, pumping out the pollen, as is Sharwil. The only
insect working the flowers is a lone Queen German wasp.
September 28th 2017
The weather is similar to yesterday, but sunnier earlier in the day.
The temperature in the shade at 0930 is 18.5oC. Last nights overnight
low was 10oC.
The Hass trees and Carmen Hass have only a rare flower open at 0930
hours - except for the 'Hass selection' (a heavier fruiting type),
which has numerous male flowers open and shedding pollen. Gwen also has
a good number of flowers open, all male and shedding. A Pinkerton tree
in a sunny location has a large number of male flowers open and
shedding, where those more shaded have almost no flowers open.
Of the 'B' pollenizer types, Edranol has a few male flowers open,
Fuerte has large numbers of male flowers open, but only some are
shedding, Sharwill is the same, but also has a few female flowers open.
Hashimoto is also male, with more flowers shedding than the other 'B'
It is clear that at this time of year, and these temperatures, the 'B'
types Fuerte, Sharwil, and Hashimoto flower most heavily, have male
flowers both open and providing pollen all day long from morning to
night. Edranol is inferior in both these aspects. In addition, Fuerte
is absolutely outstanding in its ability to attract pollinating insects
- although Sharwil is not far behind.
1300 hours - shade temperature is 21o C
Edranol has a few flowers open and shedding. Fuerte has heaps of male
flowers open -hyperfloriforous, in fact - and all shedding. It also has
a few female flowers open. The tree is well attended by bees and Polistes
wasps. Sharwil is also male flowering and shedding pollen, and it, too,
has a few female flowers open. Once again, bees and Polistes are
well present. Hashimoto has a good number of male flowers open and
shedding pollen, but there are no female flowers present.
Pinkerton has good numbers of female flowers open, attended by Polistes
(mainly). Maluma also has some flowers open, but not as many as
Pinkerton (a few bees and the odd Polistes wasp attend). Hass and Gwen
flowers are still closed.
1600 hours - shade
temperature is 17o C
Edranol and Hashimoto are male phase and shedding pollen, Fuerte is
still shedding vast amounts of pollen (its few female flowers are no
starting to close), and Sharwil is the same. Gwen is closed, and Hass,
Carmen Hass and Maluma have only a rare female flower open, but are
otherwise closed. In contrast, Pinkerton has good numbers of female
flowers open. Either Gwen and Hass opened as female and closed again
rather quickly, or it is too cool for them to open.
September 29th 2018
The lowest night temperature over the
last 2 weeks was 5oC. Fine and sunny at 0830, 15oC in the shade,
clouded over by 0900. Perfectly still.
Fuerte has been flowering for a while now, and Sharwill has also
started in earnest, and, as usual Lil Hass.
Apart from a chance
seedling, nothing else has flowers open this morning. Only L'il Hass
has insects on it, a few bees and German wasps. This tree has massive
numbers of open flowers, and may be a good nectar producer.
1430 hours - Sunny, slight
breeze, some passing cloud, shade temperature 20oC
'Select' Hass has some flowers open, in male phase and shedding pollen.
No flowers are open on the other 2 Hass trees adjacent. Fuerte remains
in male phase, shedding pollen.
1700 hours - Sun low on the
horizon, and the temperature has fallen to 12oC.
There are no insects on the avocado trees - except for a couple of
immobile steel blue ladybirds. A few female flowers are open on Hass
and Carmen Hass - and the odd male flower as well, shedding pollen.
There are a lot of female flowers open on Pinkerton, and, like Hass,
the odd male flower, shedding pollen. I sighted the first flower
of the season open on Hashimoto and on Maluma. Sharwill still has heaps
of male flowers open, shedding pollen.
September 30th 2014
Very warm, and sunny at 1415 hrs.
In fact, it was 18oC in the shade; the days high was 21oC; the overnite
low last night 10oC.
There are lots of insects about. The bees are feeding on forget-me-not
Fuerte has heaps of male flowers open and shedding, as does Sharwil.
Fuerte has a good smattering of female flowers are open, rarely seen! A
big german wasp Queen is taking some nectar, but seems easily put off
by ants. A Polistes chinensis is also feeding on it, and is
busier and more organised. The 'A' type flowers - Hass, Pinkerton,
Maluma, and Gwen are all closed. A bee and a Polistes chinensis
scramble back and forth over the closed Gwen buds, looking for a way
in. Gwen must be pumping nectar in the bud, in preparation for opening
later today or tomorrow.
October 01 2014
A warm, but windy day. Nice in the sun but
out of the wind. The days high was 23oC, the overnight low was 10oC. At
1400 hrs it was 17oC.
were quite a number of insects in the most floriferous and stinky
avocado trees, mainly German wasps, Asian wasps, and flies. There were
a number of miscellaneous insects, including the quite hairy nectar
drinker on the left (a ladybird species, possibly Rhyzobius lophanthae). It is
probably so small it moves below the level of the stigma, and is
unlikely to contact it in its wanderings.
At 1300 hrs Sharwil, Dusa, and Fuerte were flowering heavily, and all
had copious amounts of pollen clearly visible. However, while Hass,
Maluma and Pinkerton had only a few flowers open, and the vast bulk of
their flowers were closed. Gwen remained totally closed.
October 2, 2018
A warm day, sunny with some cloud.
Temperature at 1430 is 25oC, and last night's low was 10oC. These are
good temperatures for fruit set, but a bit late in the day.
lots of bees and wasps active on the flowers, but apart from Fuerte
Pinkerton and a few seedlings, flowering has not really started in
Pinkerton is in female phase at 1520, so if pollinated, pollen tube
germination and growth is starting in a time of declining temperatures.
October 3, 2018
A warm, clam day, sunny with some
cloud. Temperature at 1330 is 21oC, and last night's low was 8oC.
lots of bees and wasps active on the flowers, but apart from Fuerte
Pinkerton and a few seedlings, flowering has not really started in
1130 - Gwen is closed, but Polistes
humilis and some bees are trying to bust into the buds, so the
flowers nectaries must be very attractive at this stage.
October 4, 2018
Last night was cool, 8oC. Warm and overcast, 21oC this morning, falling
to 18oC by 1400 hours as cloud cover deepened. It is very humid, and by
1430 a steady drizzle commenced. By 1730 hours the drizzle has gone and
the clouds remain.
are a fair number of bees, wasps and flies around, but not as many as
usual. There were several Zorion sp. on the open Sharwil flowers. It
looks a little different to the common species with the white spots -
but I may be mistaken.
At 1430 Pinkerton is female phase. Sharwil is male and shedding pollen.
Late in the day, at 1730 hours, Pinkerton is still in female phase, but
I think it is beginning to close and I think male flowers may just be
starting to open. There
are still a useful number of bees on the Pinkertons, in spite of the
late hour and cool temperatures. The only other insect evident is the
9 October 2012
Sunny and a warm
northerly this morning. At 0830 it was 23oC in the shade! Past 4 days
overnite low was 9oC. By midday it was totally overcast, breezy,
cooler, 18oC in the shade.
Note: A quantum shift in the number of insects! There are far more
bees, they are staying longer, the diversity of insects is there -
flies, flower fly, bumblebee, German wasp, Asian wasp - but there are
more present at the same time. Is it the early morning heat, or do
avocado flowers produce more nectar when it is warmer? Or a bit of
both? Or are insects speeding up their life cycle?
At 8.30 in the morning there are lots of flowers open, all male. The
trees have attracted numerous insects - 3 or 4 bees, a bumblebee, a
metallic blue hoverfly, several flies, a German wasp. A small Pinkerton
tree 20 metres away is in full female flower, with lots of flowers
open. Despite being immediately next to a Lavendula dentata
hedge that has numerous bees on it, the only insects observed on the
flowers are ants. So there is some nectar there, but obviously not
enough to draw the bees off the hedge. And yet the Hass tree, 10 metres
from the hedge, is very successfully attracting bees...
By 1.30 pm there are heaps of Hass flowers open. They are all female.
The males are either non-existent, or are folding down as they close.
There are 4 to 5 bees present per tree, and the odd other visitor, such
as the 'small hover fly', and a large bodied hover fly, possibly the
three-lined hover fly.
By 4.30 pm the youngest Hass tree are still female phase, but closing
down. The air temperature is 17oC. There are still several bees in the
younger Hass trees, even altho it has been cloudy and fairly cool in
the late afternoon. The oldest Hass tree is quite some distance away,
and is shaded by some young eucalypts (not that it matters on an
overcast afternoon), and there don't seem to be any insects on its
flowers. In contrast, 12 metres away there is a Hass seedling tree that
is a mass of flowers. I have never seen a female phase on this tree, it
seems perpetually male, but whatever, it is particularly attractive to
insects. The pollen parent is almost certainly Fuerte, and Fuerte also
seems particularly attractive to insects. Anyway, 12 metres away, this
tree has at least 7 bumblebees, 5 or 6 bees, 2 or 3 German wasps, and
at least 3 blowflies, all avidly collecting nectar. And this is not a
very big tree. Admittedly the Hass tree has only a very small number of
flowers in comparison, but even so...
Pinkerton is flowering very heavily. Pinkerton was in the female phase
at 1.30 pm, and at 4.30 pm it still has a good number of female flowers
open, but is closing down. There are many 'half open/closed flowers',
either females closing or males opening. The
are being worked by a bee, a bumblebee and a German wasp.
10 October 2018
Warm, a mix of sun and cloud. The
nights have been quite cold - down to 8oC overnight. These temperatures
are forecast to continue for the next 4 nights.
Mid afternoon there were very good numbers of bees on the Pinkerton
trees. The temperatures have been such that phasing has been reversed,
and the male pollen shedding phase has been in the morning to early
afternoon. The female phase is just starting, and there is a good
overlap between the two phases, plus lots of bees. But cold night
temperatures may prevent effective self pollination. We will see.
Insect activity is in high gear today. Small hover flies (Melanostoma
fasciatum) and large hover flies (Melangyna novaezelandiae)
are in evidence everywhere. Bees are working forget-me-nots, drone
flies (Eristalis tenax) and wasps are present in good numbers,
and blowflies are about. It has been sunny, showery, hot, humid, and
breezy; the soil is moist. This would be the primo time for cross
pollination of avocado varieties.
But the only male pollen providers at this time are edranol and fuerte,
and probably Sharwil (to a lesser extent).
Hass, Reed, and Pinkerton are all in female phase at 1230. Gwen and
Esther are in female phase by 3.30 pm.
There are already some tiny little fruitlets apparently set on Reed,
and on one Hass. The jury is still out on whether anything has set on
Pinkerton - but conditions are ideal today for the late flowers to set.
We will see. (April 2012 - 2 fruit set on one tree, in an area where a
flowering Sharwil (B type) is adjacent.)
Sunny, with a cool southerly breeze. The high yesterday was 19o C. The
overnight low was 10oC. Currently it is 15o C.
At 10.00 am several bees are actively 'robbing' nectar from fat
Pinkerton terminal flower buds. These buds will open in a few hours.
There are some flowers half open/half closed, but these are not as
attractive as the buds. Even a large flower fly is forlornly flying
from bud to bud, before settling for 'second best', the half-mast
By 4:30 pm the trees are in female phase. There are are around 3 bees
per tree, a good number considering the small size of the trees. The
weather is sunny, and although there is a cold southerly blowing, the
trees a fairly well sheltered, so it feels warm.
Not many flowers remain on the Pinkerton panicles. (Note from april
2013 - initially 1 or 2 fruit set per tree, but after fruit drop 1 tree
has 2 fruit, 2 trees have 1 fruit.)
The young 'early setting' Hass has very few flowers left, but has
(apparently, at least) set a good number of terminal fruitlets over the
last 4 to 8 days. A later setting Hass 10 metres away has far more
flowers to come, but appears also to have set at least some fruit. By
1630 it is in female flowering phase, but no insects are around in this
area. Another Hass tree, which started to flower later than these two,
has a lot of flower in the upper parts of the tree. In contrast, the
panicles in the lower part of the tree are all but over.
(Note from march 2013 - the lower panicles
set only one or 2 fruit. The only fruit set are in the upper part of
the tree. Whangarei avocado growers reported that early november colder
than usual, with overnight temperature ranging between 2.5oC and 6oC.
The coldest orchards have no fruit set. Other orchards have fruit set
in the warmer parts of the orchard, but not in the colder parts. Some
early set fruit dropped when temperatures dipped in november. A
commercial orchard on our road at a lower elevation only has fruit set
in the top of the trees, the same as us. Whangarei reported that later
flowers set, but earlier flowers didn't. The pattern seems the same for
all of us.)
Sharwil has for all intents and purposes finished flowering.
Edranol is now in full swing, and its flowers overlap the period of
time when fruit are most likely to set on Hass - whereas Sharwil is no
longer effective. Bees happily move from Edranol to an adjacent
Pinkerton in female flower phase - in spite of ample other nectar
source immediately available (and being exploited by other bees).
Edranol is still shedding pollen in the afternoon, and a German wasp is
on the flowers.
Fuerte is also (still) flowering, albeit it is coming to an end. Like
Sharwil, it is almost always male and shedding pollen, no matter the
time of day.
The youngest of the two Reed trees here has commenced flowering, mainly
on the lower panicles. At 4:30 it, too, is in female flowering phase. A
bee, a worker bumblebee and a Large hover fly are in attendance.There
are already a good number of 'apparently set' fruitlets on the lower
part of the tree. (Note from april 2013 - only 10 fruit set and held on
It was cold last night, with a southerly blowing. The morning is clear
and sunny, warm out of the wind, but a bit cool in it. There are ample
pollinating insect numbers in the avocados - german wasps, Polistes,
flower flys, blow flies, and, of course, both bees and the odd worker
At 1000 hours all the 'B' type avos have flowers with 'spent' and
shrivelled anthers, the flowers half closed - except for Sharwil, whose
flowers are fully closed. The 'A' types, from Reed to Hass and
everything in between, all have male flowers, many shedding pollen.
There are no female flowers at all on the various B types, not on
Fuerte, not in various 'B' type seedlings around the place. Edranol,
also a 'B' type, is now flowering well.
By 1300 hours all the 'A' types had flowers firmly closed (except for
Hass, which had a few 'late' males open). Pinkerton seems to have a
fast turnaround - while all the flowers were firmly closed, there were
already just a few female flowers opening. In the 'B' types, Hashimoto
had some fresh males open and shedding, but not a lot. Some stigmas in
Hashimoto were brown, some white. Sharwil was the only other 'B' with a
few fresh male flowers open, albeit not all were shedding.
By 1800, with light beginning to fade and the cold night air
descending, all the 'A' type avos were still tightly closed, with the
exception of Maluma, which had just few female flowers open, and
Pinkerton, which had a lot of female flowers open. On the 'B' side,
Edranol was shedding pollen, but not many flowers were open. Hashimoto,
however, had a very good number of shedding flowers, and so did
Sharwil. However, no insects were about in the cool wind and fading
This morning is hot - 21oC at 1000 hours, sunny, cloudless, with a
Maluma is still mostly closed, but those that are open are male and
shedding pollen. Pinkerton, which had a good number of female flowers
open in the early evening yesterday is now mostly closed, barring a
smattering of knocked about flowers shedding pollen. Most of the
Pinkerton flower panicles have the majority of flowers with signs of
having set. So most the 'A' types missed female flowering yesterday
(apart from Pinkerton), but the male flowering was in the warmest part
of the day. If most flowers set at the male flower phase, then the lack
of the female stage is no problem.
It has been mixed sunny, warm, humid, and
overcast; the soil is moist after several days of intermittent warm
showers (at last - it has been rather dry for weeks). Bees have been
working Reed heavily over the last week or so. Prior to the showery
days, Reed was a wall of flowers, plastered with bees (and the odd
worker bumblebee). Conditions were ideal for fruit set - hot, humid,
night temperatures never below 10oC.
Pinkerton racemes have almost finished flowering, and are looking
skeletal. There are a few flower buds to open yet, but not a lot. The
odd bee continues to attend.
The only male pollen providers at this time are edranol and fuerte, and
probably Sharwil (to a lesser extent).
At 0900 Reed is semi-open and being heavily visited by bees. There is a
substantial smattering of female flowers open on Pinkerton.
At 1200 Hass is pretty much closed, just the odd female phase flower
open. Pinkerton has a good number of female flowers open. Maluma is
just opening a few flowers, female phase. The only male offering pollen
is Edranol, which has an abundant supply of males, shedding well. Reed
is in female phase, starting at 1230.
At 1.30 there are still a few Hass female flowers open, but sod all.
There are no insects (apart from ants) on the racemes, which is hardly
surprising given the low amount of nectar available on the tree.
Even by 1.30 there are still relatively few flowers open on the Reed,
but the sparsely distributed open flowers are well visited by bees,
albeit some bees 'bud bust' yet-to-open flowers. Clearly, Reed is a
very rewarding nectar producer, as far as bees are concerned, anyway.
In contrast, while Pinkerton still has a good smattering of female
flowers open, insects are largely absent (apart from ants).
Edranol is still chucking pollen everywhere at 1.30, but again, apart
from the ubiquitous ant, there is no obvious interest from the insect
world - in spite the good number of flowers open. Interestingly, the
modest flowering on one of the new Hashimoto trees is also in male
phase at 1.30, also with good pollen production.
There are lots of tiny little fruitlets apparently set on Reed, and on
the two young Hass trees. I'm not sure if anything much has set on the
row of Pinkertons - 'spent' flowers are hanging on in numbers, but no
sign of the little green developing fruitlet yet. I am not confident, I
have seen heaps of 'apparent sets' on Pinkerton before, only to see
them all fall off a day or so later. Conditions are ideal today for the
few remaining late flowers to set, so there is still hope.
In contrast, a younger Pinkerton tree far distant from the row has a
good number of little green fruitlets just visible under the
shrivelling flowers tepals. There is a Sharwil in-graft close by, now
finished flowering. The only difference between this tree and the
distant Pinkerton row is that there is an Edranol tree a few metres
away, flowering heavily, whereas there is no Edranol in the vicinity of
the row of Pinkertons. However, the Edranol has been flowering ever
since the Pinkerton was put in, and it has never set fruit previously,
so no conclusions can be drawn. (August 2014 - the Pinkerton row went
on to produce a very good crop, whereas the younger Pinkerton tree
adjacent the Edranol set nothing.)
It is oppressively humid, hot (21oC at 1000), totally overcast and
still. It has been warm and dry for days and days. We have not had any
rainfall other than a brief shower. The soil has once more dried out to
a deep level. Night temperatures have been a little cooler, with one
night dropping to 8oC.
Avocado flowering is essentially over except for Reed and Hellen.
We are now at the stage where the pin-head sized little set fruit are
clearly visible. It has been a 'bumper year' for Hass fruit set, and
clearly the same heavy initial set is happening on Reed. The earliest
Reed panicles are covered in little fruitlets, and the main flowering
panicles are flowering heavily and well attended by numerous bees and
the odd worker bumblebee.
Both Hass and Pinkerton are over except for the odd straggler flower
(both cultivars are female phase at 1000). Hass panicles are thick with
pinhead fruit, Pinkerton panicles have set very few fruit, and those
that have set are clearly from a few weeks ago.
Interestingly, a Sharwil in-graft in the Pinkerton row has a very
respectable number of recently set pinhead fruit. In addition, I found
a further 3 or 4 pea sized fruit, clearly set a few weeks ago (2014 -
all these fruitlets ultimately dropped off) . A small Pinkerton tree on
another part of the property is also within a metre of a flowering
Sharwil in-graft, but, in contrast, no fruit have set on that
Sharwil in-graft. The difference between the two situations is possibly
that there are several flowering seedling avocado trees opposite the
Pinkerton row, but none near the isolated Pinkerton tree. The seedling
tree 1.5 metres from the Sharwil in-graft has flowered a little before
Reed, and has only just finished. It might possibly be responsible for
cross pollination with Sharwil.
Sharwil has enormous numbers of male phase flowers, but I have rarely
seen female phase flowers in Sharwil (Edranol is the same). Sharwil may
need higher temperatures to switch to female flowering. Maybe only
female phase flowers will set. This implies the female stigma is
non-receptive in the male phase, or that it has some self sterility
mechanism with its own pollen (Sharwil produces mega amounts of pollen,
and the stigma will surely have numerous grains deposited on it in the
male phase). This implies it requires pollen from another source.
If extra heat is required to initiate the female phase, then this
explanation fails on the simple fact that it is no warmer in the
Pinkerton row in-graft than Sharwil in-grafts elsewhere on the
property, so I doubt temperature differentials explain it. If the
Sharwil in-graft in the Pinkerton row sets fruit again next year, I
will have to consider whether or not an adjacent flowering seedling is
acting as a pollenizer...but which one? Reed can't be excluded as
pollenizer, either. Mysteries abound in the world of avocado
pollination and fruit set...
The only possible male pollenizer around is Edranol, but it has only
the barest number of flowers left. A European potter wasp attends them.
Hellen is also in female phase at 1000 this morning, and the small tree
has a respectable number of flowers open. The small Reed tree 14 metres
away has 5 bees and a bumblebee on it, the Hellen has no pollinating
insects on it at all. (2014 - Hellen went on to set a heavy crop of
Reed has ejected several fruit overnight, and leaf drop has moved into
hyperdrive (along with flowering). The new vegetative flush at the tip
of the flower panicles is now really starting to move. Hass is by far
the most advanced in flushing, and speed of growth. The call on the
tree's resources must be large. I will cut most of the flush off, at
least on the Hass trees being size-trained.
If it rains, growth on the avocados will be explosive. I hope it
doesn't draw resources away from the set fruit.
As always, we will see...
November 23 2013
Hot, humid, sunny. At 0930 it is 24oC already. At 1030 it is 26oC. The
days high hit 27oC. Conditions were the same yesterday. It has been hot
for many days. There was an isolated heavy rain shower for about an
hour several days ago, but the sun came out again after it, and it has
been dry ever since.
The Reed trees flowers are mostly closed at 0930, in spite of 24oC
temperatures already. In spite of this, the avocado flowers smell
seminal, as they did yesterday morning. (Chestnut flowers have the same
odor, as do an orchid species in the genus Coelogyne, the pear
calleryana and some other plants. Apparently semen-like floral
odor is not uncommon in plants; it is said to be due to "basic
amines such as putrescine, spermine, spermidine and cadaverine".
Cadaverine and putrescine are evolved from decaying flesh, which may
explain why blowflies are initially attracted to avocado flowers.)
In spite of the heat and the smell, the number of pollinating insects
is low relative to days past. There are 3 -4 flower flies (both
species) present, 4 bees, 1 Polistes chinensis, and 1
Interestingly, the tree was in a heavy female phase at 1:00 pm
yesterday, but had an area on one side of the tree which was in male
phase. This morning (0930) those male phase panicles are now open in
the female phase. The bulk of the tree has no flowers open at 0930.
Temperatures have been consistently high for days. Yesterdays overlap
of male and female flower opening seems without obvious cause. By 2:30
pm the whole tree was in flower - in the male phase. Even although it
was hot, sunny, calm, there were almost no pollinating insects on the
tree - just 2 small flower flies, and they were not really doing much.
The male flowers were not giving out any odor, in contrast to the
Hashimoto still has some flowers open, male phase to Reeds female. It
would be the ideal pollenizer for Reed - if Reed needed a pollenizer.
But it doesn't.
November 24 2013
Hot, humid, sunny. At 1130 it is 24oC. Overnight low was 14oC. At 1130
Reed is in female phase for the second day in a row. There is no smell.
2 flower flies are present, but just flying around the panicles, not
working the flowers. in contrast, there are 4 bees on the panicles,
working well. Once again, Hashimoto is in opposite phase (male) to
Reed. Esther is also flowering well, and, like Reed, is in female phase.
November 27, 2011
Avocado flowering is essentially over, with the exception of
Fujikawa, which is barely mid flower, and Reed, which is flowering well.
Reed is setting well, in contrast to Pinkerton, which has set very few
fruit. Our tiny Gwen tree, which totally defoliated this spring, has
apparently set fruit (I expect them to fall off, either now or later).
It is very obvious that Hass and Reed are essentially self fertile,
even if fruit set is increased by cross pollination.
Pinkerton has a very long female flowering season, and Pinkerton has
flowers right through the Hass season, and maybe a little past. The
weather is warm, and there are insects around, so it is clear that
Pinkerton needs a pollinator.
First indications from our hip-high Gwen tree planted at the end of the
Pinkertons is that it may be self fertile. We have a very unhappy
Esther tree in a half barrel, and it too has apparently set some fruit,
in spite of having dropped all its leaves, so it is worth watching.
(April 2012 - nothing set)
Bees have barely been present on the flowers. In fact, it was rare to
observe a bee on the avocados this year. Even on warm, relatively calm
days, there was little bee activity on the flowers - even when they
were active gathering nectar or pollen from flowering weeds at the base
of the trees.
In contrast, it was common to find one or more German wasps working the
flowers, no matter the weather or time of day., and the same is true
for the bumblebee. The odd Asian wasp was also common, especially
earlier in the season. Flower flies and hover flies were a feature from
mid season onward. There were myriads of tiny 'gnatty' things at
certain points, always thrips, often ants, and a wide variety of other
small insect miscellanea feeding on the nectar (and in the case of the
steel blue ladybird, feeding on the pollen).
I doubt poor fruit set on some of our avocado cultivars is due to lack
of pollinating insects. It seems some avocado varieties are self
fertile, and some more or less aren't.
30 November 2013
Avocado flowering is more or less over. There was a very heavy set of
fruitlets on Hass about 3 weeks ago. Almost all of these have now
fallen over the last 4 or 5 days, and it is now clear that fruit set is
rather patchy and muted on the 2 youngest trees, but OK on the 2
oldest. The young Hass trees are heavily pruned to control size, the
older trees are either unpruned or one major branch removed regularly.
The fruit that remain are largely those that set early, probably around
mid october. These are now pea-sized or larger. There are a number of
very recently set tiny pinhead fruit on some panicles, and possibly
some may hold as very late-set fruit.
Reed has also had a huge number of flowers set to the pinhead fruitlet
stage. The youngest tree has started pinhead fruit drop, but it is too
early to tell what the retention rate will be.
Fuerte has a very large umber of fruitlets set, but pinhead fruitlet
drop has yet to start. There are still a fair number of Fuerte flowers
Hellen has now finished flowering, but is yet to shed fruitlets.
Hashimoto has also finished. There are odd rare individual 'rogue'
Hass, Pinkerton, and Maluma flowers. The first native bees have
emerged, a bit late for most avocados.
Like Hass, the Pinkertons have now shed almost all their pinhead
fruitlets. And like Hass, the only fruit to set are those that formed
about 3 weeks ago. Now the fruitlets on Pinkerton are pea-sized or
greater it is easier to see the set for the year. Each tree has at
least 12 fruit, a greater number than my first rough estimate. This is
the largest (apparent) set ever on these trees.
L. Davenport. 1999. 'A view from Florida on
avocado pollination' In: M. L. Arpaia and R. Hofshi (eds.), Proceedings
of Avocado Brainstorming. Session 5. Pollination.
Pages 101-104. October 27-28, 1999. Riverside, CA.
Hofshi Foundation. http://www.avocadosource.com.
T.L. Davenport. 2003. 'Evidence for wind-mediated, self and cross
pollination of 'Hass' avocado trees growing in Mediterranean
Proceedings V World Avocado Congress (Actas V Congreso Mundial del
Aguacate) 2003. pp. 221-226.
M. Librada Alcaraz and J. Ignacio Hormaza.
2009. 'Avocado Pollination and Fruit Set – A Perspective from Spain'
California Avocado Society 2009 Yearbook, 92: pp 113-135
Gad Ish-Am, Dan Eisikowitch. 1993. The behaviour of honey bees (Apis
mellifera) visiting avocado (Persea americana) flowers and
their contribution to its pollination
Journal of Apicultural Research 32(3/4): 175-186 (1993)
Paul D. Cooper, William M. Schaffer, Stephen L. Buchmann, 1985.
'Temperature regulation of Honey Bees (Apis mellifera) foraging
in the Sonoran Desert.'
Journal of experimental Biology.
114, 1-15 (1985) 1
Harrison, R. A. 1990. Bibionidae (Insecta: Diptera). Fauna of New
Zealand, 20, 25 pp.
Fauna of New zealand. 20.
Irvin, N. A.et al 1999. The phenology and pollen feeding of three hover
fly (Diptera: Syrphidae) species in Canterbury, New Zealand.
New Zealand Journal of Zoology 26: 105-115.
Janice M. Hickman , Gábor L. Lövei & Stephen D. Wratten. 1995.
'Pollen feeding by adults of the hoverfly Melanostoma fasciatum
New Zealand Journal of Zoology, 22:4, pp 387-392
Rader, Romina, Howlett, Bradley G., Cunningham, Saul A., Westcott,
David A., Edwards, Will. 2012. 'Spatial and temporal variation in
pollinator effectiveness: do unmanaged insects provide consistent
pollination services to mass flowering crops?'
Journal of Applied Ecology, Vol 49, 1. pp 125 - 134
F.J. Gardiazabal and S. Gandolfo. 1995. A study of self-pollination and
cross-pollination in avocado (Persea
americana Mill.) cv. Hass of different varieties.
Proceedings of The World Avocado Congress III, 1995 52-56
Munro, Martin. 2013. 'Passive pollination'.
The New Zealand Avocado Growers Journal (Avoscene), December 2013 p12
Papademetriou, M. K,. 1976. Some Aspects of the Flower Behavior,
Pollination and Fruit Set of Avocado (Persea
Americana Mill.) in Trinidad.
California Avocado Society 1976 Yearbook 60: 106-152
If you have
corrections, observations, or comments, feel free to drop a line to:
avocado [and next insert the symbol "@"] lauriemeadows "dot"
info. Apologies in advance, I don't check email very often, so
acknowledgement may be a wee while coming.