POPULATION DIFFERENCES IN BEHAVIORAL, BIOCHEMICAL AND MOLECULAR EFFECTS OF AN ACARICIDE ON HONEY BEES (Apis mellifera L.)

We investigated the impact of the acaricide Perizin (coumaphos) used to control the parasitic mite Varroa destructor, on three subspecies of honey bees: Caucasian (A. m. caucasica), Thracian (a local ecotype of A. m. carnica) and Syrian (A. m. syriaca) bees. We hypothesized that the diverse genetic backgrounds, ecological adaptations, and historical exposure to pesticides among these subspecies lead to differences in their susceptibility to coumaphos. Identifying subspecies differences in pesticide sensitivity is crucial to inform conservation strategies and optimize pest management practices in apiculture. To evaluate the effects of the coumaphos exposure, we compared learning performance, target enzyme activity, and signal and detoxification pathway gene expression in treatment and control group bees. Worker bees were exposed to single acute sublethal dose of coumaphos and then control and treatment groups were subjected to electric shock avoidance tests, and proboscis extension reflex (PER) tests to measure aversive and olfactory learning behaviors, respectively. As coumaphos is an acetylcholinesterase (AChE) inhibitor, AChE activity was also measured in the brain and midgut tissues of the bees. We also examined expression levels of six genes related to the action mechanism of coumaphos in the nervous system in brain samples, and three cytochrome P-450 genes specifically related to coumaphos metabolism in midgut samples. The results showed that coumaphos exposure had a significant impact on the bees' aversive behavior, olfactory learning behavior, and AChE activity in the midgut. The extent of these effects varied among the three subspecies of bees. Caucasian bees appeared to be the most resistant to the sublethal coumaphos exposure, while Syrian bees were observed to be the most susceptible. Thracian bees on the other hand, showed a moderate susceptibility compared to the other two. The gene expression studies showed no significant difference in brain expressions between control and treatment groups, while in midgut tissue samples, the expressions of CYP9Q1 were observed to be significantly decreased in Syrian honey bees compared to Caucasian bees. These findings support our hypothesis that honey bee subspecies differ in susceptibility to coumaphos, potentially due to variations in their metabolic detoxification efficiency. Understanding these differences is important because it contributes to better conservation strategies and helps maintain genetic diversity and resilience in honey bee populations under pesticide stress.