Topical and Oral Exposure of Chlorothalonil Induces Low Toxicity, Synergism, Inhibition of Metabolic Detoxification Activity and Gene Expression in Adult Honey Bees (Apis Mellifera L.)

Abstract

Honey bees encounter a diverse array of pesticides in their foraging areas and inside their colonies. Beekeepers have expressed tremendous concern about the impacts of pesticides on honey bee colony health and their beekeeping business. The fungicide chlorothalonil is frequently detected at high concentrations within colonies. Exposure to chlorothalonil in lab studies have shown impacts on larval development and morphology of emerging adults while field studies have shown that colony losses are associated with high levels of chlorothalonil. This research was conducted to test if chlorothalonil has effects on honey bee toxicity, insecticide synergism, detoxification activity, and expression of esterase and cytochrome P450 genes in order to assess if chlorothalonil may contribute to colony losses via direct or enhanced toxicity. Exposure to high topically applied doses and orally applied concentrations of technical or formulated chlorothalonil did not result in significant direct toxicity, showed low levels of both synergism and antagonism, and did not impact activity or expression of detoxification enzymes. Therefore, the impacts of chlorothalonil on honey bee colony health is likely not due to toxicity or synergism but rather other physiological mechanisms.

Keywords: Chlorothalonil, Honey bee, toxicity, synergism, esterase, cytochrome P450