In recent years there has been increasing research into the impacts of pesticides on pollinators, but relatively little research into the effects of the pesticides used by beekeepers to treat their hives. Honeybee colonies are routinely treated with chemical miticides to control the parasitic mite Varroa destructor, but little is known about the long-term impacts of miticides on honeybees and their colonies, especially in apiary settings.
Researchers in Australia compared the effects of the commercial miticides tau-fluvalinate (Apistan) and thymol (Apiguard) on honeybee colonies and bee foraging behaviour. Their experiment ran from April to August: a five-month period from late autumn to the end of winter.
They found that autumn treatment caused no significant change in adult bee or brood population, bee longevity, or mass of food stores. The colonies treated with thymol weighed significantly less at the end of the treatment and in the following summer, but not during spring. The average temperature of the thymol group was also significantly lower than the control group during winter. The bees in the tau-fluvalinate group and thymol group performed significantly more foraging trips during their lifetime, and tau-fluvalinate treatment was found to cause the bees to start foraging earlier in life and perform shorter trips.
The researchers conclude that autumn thymol or tau-fluvalinate treatments had minor effects on bees and bee colony performance. However, they caution against long-term reliance on chemical miticides as residues accumulate within hive products such as pollen, wax and honey.
Read the full paper:
Colin, T., Forster, C.C., Westacott, J., Wu, X., Meikle, W.G. & Barron, A.B. 2021 Effects of late miticide treatments on foraging and colony productivity of European honey bees (Apis mellifera). Apidologie, 52, 474–492. https://doi.org/10.1007/s13592-020-00837-3