Circadian and seasonal changes in honeybee (Apis Mellifera) worker susceptibility to pyrethroids

Abstract

We examined the susceptibility of the worker honeybee Apis mellifera L. to pyrethroids. Bees were intoxicated by selected synthetic pyrethroids (active substances: beta-cyfluthrin, deltamethrin, alphacypermethrin, lambda-cyhalothrin, esfenvalerate, and bifenthrin) and 72 hours after intoxication the number of surviving insects was determined. It was observed that the susceptibility of the honeybee to pyrethroids (expressed herein as the survival rate) was changing in diurnal rhythm, ranging from 100% (for a majority of substances in both seasons) to 11.1±0.37% (deltamethrin) and 11.1±0.73% (esfenvalerate) in spring, and 11.1±0.73% (esfenvalerate) and 4.6±0.17% (bifenthrin) in summer. The lowest susceptibility of bees to pyrethroids occurred during the night, when the honeybees were characterized by reduced motility and did not fly out for foraging, whereas the highest susceptibility was observed during the day, a natural time for seeking food. Along with diurnal changes in the susceptibility described above, differences dependent on the seasons in which the intoxication took place were also observed. Insects intoxicated in summer were less susceptible to pyrethroids than those intoxicated in spring.