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Date: | Fri, 21 Apr 2023 12:17:15 -0400 |
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According to B. Nganso, in her work in South Africa:
>hygienic and grooming behaviours could not explain the lower mite infestation levels recorded in A. m. scutellata colonies. The suppression of the reproductive success of Varroa mite in the worker brood cells by A. mellifera populations is a crucial adaptive resistant mechanism
> an increase in the percentage of infertile mites over time (from 13 to 30%) has been reported as a parameter that suppresses the mite reproduction in worker brood cells of the surviving A. m. scutellata population in South Africa
> lower reproductive output was mainly due to the high mite infertility rates and percentage of unmated daughter mites as well as low mite fecundity recorded in infested cells.
> factors such as suppression of the mite’s reproductive success and/or lower viral prevalence within honeybees and mites might better explain the variability in the mite infestation levels observed between both A. mellifera subspecies and should be evaluated in future studies.
To me this suggests the possibility that these bees and these mites have co-evolved, meaning we are looking at distinct populations of bees —and— mites. A change in mite behavior alone could manifest in the way described above. A selected population that has far lower reproduction could successfully live in honey bee colonies because 1) it doesn't kill them and 2) it's slipping under the radar. Lowered reproduction could benefit the colony by enabling them to keep the mites in check, and could benefit the mites since they are still reproducing but at a lower rate.
Again, Nganso points to suppressed mite reproduction but does not suggest a mechanism for it. I suggest it could be natural selection on the mites which generated a more benign sub-population. On the other hand, it might be that the African bees' hygienic behavior is the actual driver, inasmuch as they are killing off a large part of the mite population. The resulting population may have been selected for behaviors such as we are seeing here. That's why I posed the question of whether there are distinct mite/bee populations which might account for the type of things people are seeing in So. Africa, PR, and Cuba.
PLB
Nganso, B. T. (2018). Mechanisms of resistance and tolerance in African and European honeybees Apis mellifera L., against Varroa destructor. (Doctoral dissertation, University of Pretoria).
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