Interaction of chlorothalonil and Varroa destructor on immature honey bees rearing in vitro

Under realistic environmental conditions, bees are often exposed to multiple stressors, especially Varroa destructor and pesticides. In this study, the effects of exposure to NOAEC of chlorothalonil during the larval stage, in the presence or absence of V. destructor, was examined in terms of survival, morphological and transcriptional changes. The interaction between chlorothalonil and V. destructor on the survival of honey bee was additive. V. destructor are the dominant factor in the interaction for survival and transcriptome alternation. The downregulation of the genes related to tissue growth and caste differentiation may directly link to the mortality of honey bees. Either chlorothalonil or V. destructor induces the irregular morphology of trophocytes and oenocytes in the fat body. In addition to irregular shapes, oenocytes in V. destructor alone and double-stressor treatment group showed altered nuclei and vacuoles in the cytoplasm. The interaction of V. destructor and chlorothalonil at the larval stage have potential adverse effects on the subsequent adult bees, with up-regulation of genes involved in lipid metabolism and detoxification/defense in fat body tissue. Our findings provide a comprehensive understanding of combinatorial effects between biotic and abiotic stressors on one of the most important pollinators, honey bees.

Automated summary

This study investigates the combined effects of Varroa destructor and chlorothalonil exposure on honey bees. It found that the interaction between V. destructor and chlorothalonil had an additive effect on honey bee survival and gene expression. Downregulation of genes related to tissue growth and caste differentiation may contribute to the mortality of honey bees. The study also observed abnormal morphology and altered nuclei and vacuoles in the fat body tissue of honey bees exposed to V. destructor and chlorothalonil. These findings highlight the potential adverse effects of biotic and abiotic stressors on honey bees.