Effect of Sublethal Doses of Clothianidin and/or V. destructor on Honey Bee (Apis mellifera L.) Health, Behavior and Associated Gene Expression
Autor: Morfin Ramirez, Nuria
Department: School of Environmental Sciences
Program: Environmental Sciences
Advisor: Guzman-Novoa, Ernesto
Little is known about the effects of sublethal doses of neonicotinoids on honey bee (Apis mellifera L.) behaviors and mortality, and whether those effects are altered with parasitism by V. destructor. This study examined the effects of multiple exposures to field-realistic sublethal doses of clothianidin with and without V. destructor on adult bees and newly emerged bees treated as larvae. For adult exposure, memory retention decreased with each stressor alone, but weight and sugar consumption decreased only by the effect of V. destructor. For larval exposure, haemocyte counts increased with clothianidin but decreased with V. destructor, clothianidin reduced hygienic behavior and the number of foraging trips of the adults that emerged. Interactions between the stressors were observed as decreased weight of newly emerged bees with larval exposure, an increased mortality in adult bees, and a decreased intense grooming behavior with adult exposure. The relative expression of several immune and neural related honey bee genes showed an interaction between the stressors using two-way ANOVA in many cases. Also, the dose response of gene expression often revealed a non-linear pattern, implying hormesis, although hormesis was not detected for any of the biological measurements. For example, AmpUf68 expression in newly emerged bees showed an interaction between the stressors with a J-shaped dose response to clothianidin and no dose response to clothianidin plus V. destructor, while AmDef-2 expression in adults showed an interaction between stressors with an inverted U-shaped dose response to clothianidin and a sigmoidal dose response to clothianidin plus V. destructor. RNAseq analysis of bees with the highest sublethal doses of clothianidin with and without V. destructor showed no changes in the magnitude of expression but reduced numbers of differentially expressed genes with the combined stressors compared to each stressor alone. However, novel differentially expressed genes were also observed with the combined stressors. The combined stressors appeared to both change and inhibit the numbers of differentially expressed genes compared to each stressor alone. In general, clothianidin and V. destructor have different effects on bee health and behavior that was only rarely affected when combined, whereas gene expression mostly had reduced and unpredictable, rather than additive, effects with the combined stressors.