Synergistic effects of imidacloprid and high temperature on honey bees

Neonicotinoid exposure can disturb honey bee physiology while there has been no case that sole exposure of field-realistic dose led to colony collapse. Therefore, synergistic effects of other stress factors such as varroa mite and virus disease with neonicotinoid have been focused on in recent years. High temperature is also a candidate for the synergism. Abnormal high temperature caused by rapid climate change could boost the hazardous effects of neonicotinoid on honey bees. Here, to investigate synergistic effects of imidacloprid and high temperature on honey bees, bee hives were exposed to imidacloprid (20 ppb) and high temperature (41 ºC) simultaneously. In three independent experiments, one set of hives showed a failure of thermoregulation following the simultaneous treatment, inner temperature of it increasing up to 41 ºC. The expression levels of heat shock proteins, which were constant following imidacloprid treatment at normal temperature, showed significant difference between the control and imidacloprid-treated groups in high temperature. Transcriptome analysis revealed that protein synthesis, olfactory sensing, and signaling pathways, which were intact by either imidacloprid or heat shock treatments, were modified following the simultaneous treatment. These suggest that bee hives exposed to neonicotinoid may exceed the threshold under abnormal heat wave, leading to colony collapse disorder.