in the last episode of Inside The Hive.tv we learned that in 1987 researchers described for
the first time that Apis cerana the asian honeybees are capable to defend themselves
against varroa mite using grooming and removal of infested brood cells, hygienic behavior. After
thousands of years battling this mite evolution by natural selection selected genetic traits in the
asian honey bees and researchers kept digging to find more information about it to perhaps help the
european honey bee throughout breeding programs. After more research, few people couldn't imagine
what else Apis cerana, the asian honey bee, were capable doing to fight varroa mites.
in 1990 researchers working in thailand published a scientific article showing the results of a
series of interesting experiments. Observation in a field suggests that the varroa mite infestation
in Apis cerana honeybees were quite different than Apis mellifera, the european honeybees,
researchers observed that varroa mite were rarely found inside worker cells of Apis cerana the asian
honeybees, the great majority of infested cells were drone cells the male honeybee.
That's not the case of Apis mellifera, where worker bees
are also heavily infested even though varroa mite show some preference for drone cells.
if the observations are correct it will be very interesting for beekeepers to know what
is happening inside the hive that makes varroa mites not able to infect workers honeybee cells.
To confirm the observations researchers artificially infested worker and drone
brood cells containing 50 instar larvae with female varroa mites . And the conditions of
the cells were recorded daily. In the first round of experiments live varroa mites were placed into
worker and drone cells and in a second round of experiment dead varroa mite were used instead. The
results confirmed previous observations from other researchers, as we saw in the video number two of
this video series. Apis cerana is highly efficient to remove varroa mite infested worker cells.
After six days of infestation almost 99% of the artificially infested cells were removed by Apis
cerana compared with only 12.5 % of the controls. Here is a surprising result. Interestingly
similar results was obtained using dead varroa infestation as well where 91.9 of the artificially
infested cells were removed in about five days. These results strongly indicates that just the
presence of varroa mite is enough to trigger the hygienic behavior and this might be one of
the main reasons why Apis cerana tolerate varroa mite infestations so well. However, the same is
not true in Apis cerana drone cells infestation, where they found that only 25% of the cells that
were artificially infested were removed compared with around 50% of the controls. Apis cerana
remove infested worker cells very efficiently but the same is not true with drone cells. And also
this behavior seems to be independent of an active varroa mite parasitism because
dead varroa mite inside the cells also trigger the hygienic behavior. What triggers the behavior?
mite smells? if so why doesn't the infestation in drone cells trigger the hygienic behavior?
In a third experiment researchers freeze both workers and drone cells to compare the differences
in hygienic behavior without the presence of varroa mite. Surprisingly Apis cerana honeybee
remove all dead worker brood cells in about 24 hours after freezing, and only 34% of the
drone brood in 16 days of observation showing that independently of an active varroa mite infestation
or the single presence of the mite Apis cerana are very efficient to remove damaged worker bees
but the same is not true for drone brood cells. Why do Apis cerana does not remove damaged drone
cells at the same rate as damaging worker cells? The authors suggested Apis cerana worker bees
might have difficulties to open the walls of drone cells as an explanation for the results observed.
My personal opinion is that hygienic behavior toward drone cells might be limited, also as the
consequences of natural selection, so it might be disadvantageous for the overall reproduction
successful rate of these bees in nature and therefore Apis cerana that were able to remove
drone cells in the same rate in the past were eliminated by natural selection. I am speculating
here and I would love to know what your thoughts are. What do you think is happening? Please let
me know in the comment section. In this video series we are looking at the historical aspect
of varroa mite resistant honeybee programs. It is my goal here to show you several key research
articles that led us where we are today in our understanding on varroa mite biology and honeybee
genetically traits for breeding programs. I'm Dr. Humberto Boncristiani and I want to invite you to
subscribe to the channel if you see value. Apis cerana the asian honey bee has already developed
several physiological and behavioral traits to obstruct the reproduction success of varroa mites.
We learned from video one that breeders in the past didn't know what traits to look at in their
breeding programs to select varroa resistant honeybees. In video number two we learned that
asian honeybees has already traits related with varroa resistance selected that could be useful to
help the european honey bees. For example grooming where bees are able to find and remove varroa
mites from adult bees and hygienic behavior where infested brood are removed from the nest. What
else does Apis cerana have to teach us about mite control. If you're a patreon of mine you already
know and if you're not you can wait watching this video right here. It's great to have you here,
thanks for watching, Inside the hive.tv the show about bees. See you guys next week