NEONICOTINOID TOXICITY IN REPRODUCTIVE HONEY BEE CASTES
Date
2022-06-22
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
ORCID
0000-0002-6802-2762
Type
Thesis
Degree Level
Doctoral
Abstract
High pollinator losses of recent decades have been attributed to several causes including increased exposure to pesticides, particularly neonicotinoid insecticides. This has spiked re-evaluation of neonicotinoid use in agriculture and has heightened the need to enhance pesticide risk assessment. Currently, pesticide risk assessment for pollinators is based on assays focused predominantly on worker bee mortality in response to pesticide exposure. This approach has been criticized for overlooking sublethal toxic effects and its lack of proper evaluation of the reproductively active honey bee drones and queens. Accordingly, the overarching goal of this thesis was to incorporate the evaluation of honey bee reproductive castes in toxicologic assays through the use of “gold standard” research techniques routinely used in vertebrate toxicology studies. First, we reviewed, documented, and summarized the normal anatomical structures of the mated queen reproductive tract in order to establish reference material of the normal morphology expected in healthy queen bees. Next, we investigated the effect of thiamethoxam (THI), a commonly used neonicotinoid, on developing queens. We found that direct THI toxicity in queens can result in hypoplasia of the pheromone producing mandibular glands. Such morphologic organ changes precede compromised organ function. Therefore, it is reasonable to hypothesize that dysregulation and disruption of pheromone production in intoxicated queens may partially explain the increased queen failure rates reported by beekeepers in association with high colony losses. Importantly, this study highlights that THI can have a direct negative effect on queen bees, indicating that it may be prudent to include all castes in pesticide risk assessment. This finding is further supported by our final studies, where we describe that THI toxicity is highly caste and age specific. Namely, we found that developing (i.e., larval) queens are highly sensitive to THI toxicity, but become more resilient following emergence. The opposite was found to be true for drones. Furthermore, detoxification enzyme activity in bees is similarly caste and age specific, although the enzymes tested in our studies did not change in response to THI treatment. Overall, these finding indicate that using worker bees alone in pesticide risk assessment may be suboptimal since toxicity in workers may not fully reflect toxicity observed in other honey bee castes. In addition, applying histologic and biochemical assays in pesticide risk assessment can potentially enhance our understanding of bee toxicity, improve the detection of sublethal toxic changes, and assist in the establishment of safe dose ranges of pesticides to protect pollinators while ensuring proper protection of agricultural crops.
Description
Keywords
Apis Mellifera, caste, neonicotinoid, risk assessment, histology, reproductive
Citation
Degree
Doctor of Philosophy (Ph.D.)
Department
Veterinary Pathology
Program
Veterinary Pathology