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.
of avocado cultivar 'Sharwill' 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
Modified from Wikipedia image
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
On its first ever opening, the flower opens as a female; all
9 male stamens lay down flat and tight against the green
tepals, leaving the the female ovary, style and stigma very
exposed. After some hours, the flower closes.
It remains closed until the following day, when it opens
again in the pollen shedding 'male' phase, although the
female parts may still be receptive. After some time, the
flower closes for the second, and last, time. It then either
withers and falls off, or becomes 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. 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 female phase of the
flower ends when the flower closes 1 or 2 hours later. The
same flower re-opens the next day, but as a male, shedding
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 flower phase can vary greatly in opening and
closing time on any given day.
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 gender phase.
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
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
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
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 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. 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, and very likely needs a
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. Sharwill) 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 Sharwill 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
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 the overlap.
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
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
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
Male and female flower parts receptivity
Overlap between the separate male and female flowering
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
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
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
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 trees.).
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
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
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
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
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.
Southern Florida, shaking branches at the time of pollen
shed increased fruit set and retention over unshaken
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 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.
experience here at Helensville can be summarized as
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 day, and
4. There are more insects on the flowers later in
the season when the weather is warmer and the days
5. Some varieties clearly produce more nectar than
others, and are therefore more attractive to insects
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 time),
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 Dilophus
nigrostigma, seventh was the hover fly Melanostoma
fasciatum, and eighth was another native bee,
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
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.
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 flies. Only
is abundant here, and while it is low on the ranking
of the 'top 8', it does appear as the avocado
blossom season starts.
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
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
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
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
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. 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
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,
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
Around 10 species of solitary bees are one of the
primary pollinating insects in the humid subtropical
forest that is the native habitat of the avocado.
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
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
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
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 flowers.
Nectar collecting bees visiting flowers
that are shedding
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
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
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 subterminal flowers.
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 Ettinger.
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 orchards.
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 their bodies.
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. 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. Whie an effective pollinator, it is not
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
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
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
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 avocado trees.
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
Threelined Hover fly on an avocado leaf, basking and
cleaning after a sweet meal.
Some notes and observations on flowering and insect
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 were observed.
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.)
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
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 are developing.
May 17, 2012
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 morning.
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
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 panicle.
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
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
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 leaving.
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 opens.
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
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
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
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
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 blossom.
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
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
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
September 21 2013
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, Sharwill, 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 shedding.
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
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
bumblebee, at least 5 bees, and around 4 Asian
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 Sharwill tree in a
tub and a branch of Sharwill 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 Sharwill,
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.
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
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 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
November 02, 2011
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 sharwill (to a lesser
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 Sharwill (B type) is adjacent.)
November 3, 2012
Sunny, with a cool southerly breeze. The high yesterday
was 19o C. The overnight low was 10oC. Currently it is
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
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
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.)
Sharwill has for all intents and purposes finished
Edranol is now in full swing, and its flowers overlap
the period of time when fruit are most likely to set on
Hass - whereas Sharwill 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 Sharwill, 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 the tree.)
November 07, 2013
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
The only male pollen providers at this time are edranol
and fuerte, and probably sharwill (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
Sharwill 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 set adjacent the
Edranol set nothing.)
November 17, 2013
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
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 a go.
Interestingly, a Sharwill 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 Sharwill in-graft, but, in
contrast, no fruit have set on that Sharwill
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 Sharwill in-graft has flowered a little
before Reed, and has only just finished. It might
possibly be responsible for cross pollination with
Sharwill has enormous numbers of male phase flowers, but
I have rarely seen female phase flowers in Sharwill
(Edranol is the same). Sharwill 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
(Sharwill 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
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 Sharwill
in-grafts elsewhere on the property, so I doubt
temperature differentials explain it. If the Sharwill
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
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
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
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 species Pyrus
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 bumblebee.
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 female
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 paniciles,
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
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
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
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
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 open.
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
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Rader, Romina, Howlett, Bradley G., Cunningham, Saul A.,
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F.J. Gardiazabal and S. Gandolfo. 1995. A study of
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December 2013 p12
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