DOI: 10.5061/dryad.7m0cfxq0j
title: Impacts of neonicotinoid insecticides on bumble bee energy metabolism are revealed under nectar starvation

description: 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.
description: In this study, we used a metabolomic approach
 to examine how sublethal, field-realistic exposure (5 ppb) to the
 neonicotinoid insecticide imidacloprid, on its own and alongside
 starvation stress, influences energy metabolism in the common eastern
 bumble bee Bombus impatiens. Individual worker bumble bees (n = 195) were
 assigned to one of four insecticide treatment groups: 1) sustained, 2)
 limited-early, 3) limited-late, and 4) untreated (control). All bees first
 underwent a seven-day exposure period wherein they were provided with
 either treated (sustained, limited-early, limited-late) or untreated
 sucrose solution (untreated; control group) according to their treatment
 group. After the seven-day exposure period, all bees underwent an
 experimental starvation period. A subset of bees from each treatment group
 was immediately collected (0-hour group) to determine how imidacloprid
 exposure alone impacts bee metabolite levels in the absence of starvation.
 We then subsequently collected subsets of bees from each treatment group
 at one of three additional starvation time points, separated by eight-hour
 intervals, at 8, 16, or 24 hours following the refeeding period. Bees were
 collected in liquid nitrogen and sent to the UC Riverside Metabolomics
 Core Facility for metabolomic analyses targeting central carbon metabolism
 to assess how metabolites involved in sugar energy metabolism are
 influenced by insecticide exposure.