Pressure on pollinators: an examination of bumblebees (Bombus spp.) and systemic insecticides, parasites, and agricultural habitats

Abstract

Bumblebees (Bombus spp.) pollinate a variety of wild floras and agricultural crops. However, some species are in decline due to a variety of interacting stressors: climate change, habitat loss and degradation, parasites and disease, and pesticides. Pesticides, particularly the neonicotinoids, a group of systemic insecticides, have been implicated in declines of European bumblebee species, but the effects of systemic insecticides are less clear for many North American species. One aim of this thesis was to determine the relative acute oral toxicity of systemic insecticides on Bombus impatiens (Cresson, 1863) workers in comparison to honey bee workers (Apis mellifera Linnaeus, 1758). Thiamethoxam was observed to be the most acutely toxic, followed by sulfoxaflor, flupyradifurone, and cyantraniliprole. A secondary aim was to determine if thiamethoxam fed to wild B. impatiens and Bombus bimaculatus (Cresson, 1864) queens for 14 days would result in any changes in the queen’s ability to establish and maintain a colony for reproduction. However, many queens died during the experiment, preventing statistical analysis of the surviving colonies’ outputs. In an ancillary aim to record parasite prevalence in queens, conopid larva and tracheal mites were not as commonly detected as nematodes and external mites. A third aim was to determine the usage of conventionally managed farm field margins by bumblebee queens. More bumblebee queens were observed foraging in farm field margins than in the paired natural areas, although more bumblebee queens were observed nest searching in the natural areas. A fourth aim was to compare the bumblebee species captured with different sampling techniques. Active (targeted netting) and passive (Blue Vane Traps, BVTs) sampling were completed in conventionally managed farms and paired natural areas. There were no differences in species richness caught between the two sampling techniques, however, when comparing sampling technique and site combinations, significantly greater species richness was found in passively sampled natural areas. In contrast, a significantly greater abundance of bumblebees was caught with active sampling in natural areas than in farms, but there was no difference between the sties when sampling with BVTs.