A Pilot Study Investigating the Effects of Sublethal Doses of Imidacloprid on Honeybee Larvae: Survival and Cleaning Behavior in Nurse Bees

Honeybees are important pollinators that appear to be threatened by the widespread use of neonicotinoid pesticides such as imidacloprid. The sublethal effects of imidacloprid on adult bee foraging effort and navigational abilities are well known. Recent studies of imidacloprid-induced winterkill revealed that bioaccumulation in hive reserves affects colony survival. We hypothesized that larvae fed pollen and nectar contaminated with sublethal doses of imidacloprid may not develop normal cleaning behavior which may lead to increase of unavailable brood cells. Larvae by matched queens were divided into control and imidacloprid treatments. Larvae in the imidacloprid treatment were fed 1/100 of the LD50 (0.18 ng/larvae) in 1.5 M sucrose whereas control larvae were fed only 1.5 M sucrose. Larvae were fed 5 uL daily for 5-6 days before pupation and were maintained in hive frames. We subsampled 20 larvae for HSP70 assays and the remaining larvae pupated and emerged in an incubator. Capped larvae and  adult mortality was higher in imidacloprid treatments than control treatments. There were so significant differences for emergence pupae rate and pupae mortality between both groups. When new nurse bees were tasked with cleaning 20-30 cells contaminated with hive dust, nurses fed imidacloprid as larvae cleaned fewer cells than nurses in the control treatment. Our preliminary results suggest that larvae exposed to sublethal doses of imidacloprid exhibit latent effects on adult performance traits important to hive maintenance and survival. If confirmed in future studies, this may inform predictive models of colony collapse disorder.