Impacts of neonicotinoid insecticides on bumble bee energy metabolism are revealed under nectar starvation

Bumble bees are an important group of insects that provide essential
pollination services as a byproduct of their foraging behaviors. These
pollination services are driven, in part, by energetic exchanges between
flowering plants and individual bees. Thus, it is important to examine
bumble bee energy metabolism and explore how it might be influenced by
external stressors, which contribute to declines in global pollinator
populations. Two stressors that are commonly encountered by bees include
insecticides and nutritional stress. Our study examines the effects of
neonicotinoid insecticide exposure alone, and in combination with
nutritional stress, on bumble bee metabolism using a novel metabolomic
approach. We hypothesized that exposure to the insecticide imidacloprid
would disrupt bumble bee energy metabolism, leading to changes in key
metabolites involved in energy metabolism. We exposed Bombus impatiens
workers to imidacloprid according to one of three exposure paradigms
designed to explore how sustained versus more limited imidacloprid
exposure influences energy metabolites. After bees were exposed to
imidacloprid, they were subjected to artificial nectar starvation. Our
results showed that the strongest effects of imidacloprid were observed
when treated bees also experienced artificial nectar starvation,
suggesting a combinatorial effect of neonicotinoids and nutritional stress
on energy metabolism. Overall, this study provides important insights into
the mechanisms underlying the impact of neonicotinoid insecticides on
bumble bees and underscores the need for further investigation into the
complex interactions between environmental stressors and bee metabolism.