THE MOLECULAR SECRETS OF HONEYBEE IMMUNITY

The southern part of the United States is home to a particularly interesting population of survival bees, because this region is a hybridization zone between susceptible European honeybees kept by beekeepers throughout the US for pollination and honey production, and Varroa tolerant Africanized honeybees, which escaped from a lab in Brazil 1957 and have since successfully spread throughout South and Central America. Africanized honeybees are remarkably tolerant against a range of different biotic and abiotic stressors, but their increased levels of defensiveness precluded their widespread use as domesticated stock so far. Because Africanized honeybees are less cold tolerant compared to European bees, they are restricted to the Southern parts of the US, where they continuously hybridize with managed bee stock. A recent genetic study confirmed that these bees are genetic hybrids of at least four different bee genotypes, making them one of the most genetically diverse bee populations in the world. Furthermore,unlike other Africanized bee populations, these bees are under continuous selection for low defensiveness because they live primarily in urbanized areas, similar to an island population that has become gentle over time.This is a natural consequence of human-mediated selection: aggressive hives are eliminated by eradicators, and beekeepers replace queens of defensive hives, leaving the most docile genotypes to reproduce. The survival bees therefore offer a unique opportunity to study life history traits of economic interest.Theaim of our proposed work is to determine the mechanistic basis of the unique parasite tolerance traits in survival bees. As a first step, we have already brought unique survival bee genotypes into management at UC Riverside and adapted our bee keeping management practices to their needs. Amassing these resources is a direct result of ongoing collaborative links with local beekeepers.We conducted pilot experiments that confirmed infection intensities of Varroa mites to be 4-5 times lower compared to managed bees, and mite loads are also significantly lower on the colony level. We most recently confirmed that Varroa tolerant African (i.eA. m. scutellata)and Eastern (i.e.Apis ceranae) honeybees recognize mite infestations and respond with specific innate immune responses, that differ from susceptible European bees. We predict that these proteomic differences are the key for the observed increased mite tolerance. Several other recent publications identified other promising molecules/biomarkers that seem to play a role in defense against Varroa infestations. Some, such as chitinases were found to be associated with targeted immune responses, while others, such as the semiochemicals tritriacontene, hentriacontene, heptadecene or pentadecene, were found to mediate Varroa sensitive hygienic behaviors that reduced mite infestations at the colony level. Six cuticular hydrocarbons of bee larvae were also found to be specific to Varroa parasitization-triggering hygienic behaviors.However,we do not know if local survival bees use similar mechanisms, or if they possess unique traits that are more immediately useful for breeding and other applications due to co-selection for docility and parasite tolerance. Our proposed work will address this key knowledge gap. Outcomes of this work will be important for future stock selection and breeding purposes. More broadly, improving parasite tolerance in managed bees is a sustainable way to safeguard pollination services, as lower parasite loads will also reduce parasite movement between managed and unmanaged pollinator species.