The adverse impact on lifespan, immunity, and forage behavior of worker bees (Apis mellifera Linnaeus 1758) after exposure to flumethrin.

Several pyrethroids (such as flumethrin and fluvalinate) with low toxicity to honey bees and comparable high toxicity to mites are used worldwide as acaricides. However, flumethrin has been used for a long time in colonies to control Varroa destructor and the honey bees might be exposed to flumethrin cumulatively, which could affect the health of honey bee colonies. This study evaluated the potential adverse effects of direct flumethrin exposure on worker bees under laboratory and colony conditions. Under laboratory conditions, downregulation of genes related to immune was observed when worker bees were exposed to flumethrin above 1/16 LD; at levels above 1/8 LD, olfactory learning was impaired, and genes related to learning memory were downregulated; and at >1/4 LD, their lifespan was shortened. Monitoring with radio frequency identification (RFID) revealed that worker bees in a colony exposed to flumethrin above 1/8 LD had a shortened lifespan and reduced foraging ability. When worker bees are exposed to >1/4 LD of flumethrin, it can lead to excessive rest day behavior. These results indicate that applying flumethrin in colonies may pose a severe health risk to honey bees and reveal the urgent need to develop non-toxic and highly effective acaricides.