Global bumble bee declines pose ecological risks to biodiversity and reductions in agricultural crop yields. These declines have been linked to the widespread use of neonicotinoid pesticides which are shown to cause cognitive impairment and foraging inefficiency in several Bombus species. Studies examining acute imidacloprid exposure suggest that neonicotinoid pesticides may influence hive task assignment by lengthening the time needed for tasks and promoting specialization of a eusocial species. Extended behavioral studies on pesticide effects on within-hive task specialization and conflict are required to determine the long-term effects on hive social structure. In this study, the effects of exposure to field realistic levels of sulfoxaflor on B. impatiens within-hive task assignment and reproductive conflict were studied. Task specialization, activity levels, aggressive behavior, and body mass in hives with access to either pure nectar and un-dosed pollen or nectar and pollen dosed with field-realistic levels of sulfoxaflor (5 ppb in nectar and 50 ppb in pollen) was examined for two weeks after exposure. We documented the behaviors of 10 individuals for 10 randomly selected 1-minute subsamples of 4-hour evening (11-3am) recording period. The body mass of 20 newly emerged individuals was measured to examine if within-hive task behavioral influenced body size.
Results/Conclusions
Contrary to our predictions, individuals exposed to sulfoxaflor did not exhibit increased task specialization. There was also no difference in overall activity or incidence of aggressive behaviors. However, individuals exposed to pesticides were less likely to engage in guarding, suggesting that sulfoxaflor may influence task assignment, with fewer individuals guarding the hive. Reductions in guarding behavior have significant implications for hive success in the wild. Guarding behavior is an important first line of defense against invading species that may attempt to usurp the queen. In this laboratory experiment, there was no change in newly emerged worker biomass or colony productivity due to pesticide exposure. However, wild colonies could be negatively affected if protection against predators is weakened. Previous studies indicate negative effects of neonicotinoids on bumble bee activity and mobility. Our results suggest that sulfoxaflor may not influence task specialization or activity levels, but may result reduced colony defense against predators.