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Submitted to: Physiological Entomology
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 10/24/2018 Publication Date: 1/8/2019 Citation: Cook, S.C. 2019. Chemical and dose-dependent effects of two neonicotinoids on honey bee metabolism. Physiological Entomology. 10(1):18. https://doi.org/10.3390/insects10010018. DOI: https://doi.org/10.3390/insects10010018 Interpretive Summary: A recently introduced class of pesticides, neonicotinoids, are present in low doses in honeybee collected pollen and nectar, and are suspected of playing a significant role in recent honeybee declines. Neonicotinoids act as agonists to nicotinic acetylcholine receptors of post-synaptic neurons of the insect central nervous system, and disrupt motor, sensory, and other neuronal systems in exposed insects, including bees. Recent studies have shown however, that sub lethal exposure to neonicotinoids can also affect adult honeybee immunity and metabolic physiology of larvae. Very little is known of the effects of neonicotinoids on the metabolic physiology of adult bees. From experiments of caged young adult worker bees exposed orally to sub lethal doses of two neonicotinoid pesticides, imidacloprid and clothianidin, over two weeks, we found they significantly affected measured aspects of honeybee metabolic physiology in a dose-dependent fashion. Bees exposed to low doses consuming significantly less protein food, and greater amount of sucrose solution. A dose dependent effect was also observed in worker protein and lipid content, with bees having significantly less protein and more lipids when exposed to high doses of both pesticides. Both low and high doses, but not mid-level dose of imidacloprid resulted in greatly reduced worker respiration over time. Only the low dose of clothianidin significantly lowered bee respiration rate. This research shows that very low doses of neonicotinoids can impact honeybees in ways that are not immediately lethal. Future regulation of use of neonicotinoids should consider effects of these pesticides on honeybee metabolic physiology because effects to individual bees will have reverberating effects on whole colonies. Technical Abstract: Residues of systemic neonicotinoid pesticides are present in honeybee collected pollen and nectar, and are suspected of playing a significant role in recent honeybee declines. Studies have shown the effect of acute exposure on honeybee worker memory, learning, and motor skills, effects expected from pesticide mode of action on the insect central nervous system. Recent studies have shown however, that sub lethal exposure to neonicotinoids can also affect adult honeybee immunity and metabolic physiology of larvae. Little experimental work has been conducted that explicitly tests hypotheses of the effects of sub lethal neonicotinoid exposure on honeybee metabolic physiology. Here, we present findings from laboratory experiments using caged newly emerged honeybee workers exposed orally to a range of sub lethal doses of two neonicotinoids, either imidacloprid or clothianidin in foods. Over two weeks we quantified food consumption, change in worker lipid and protein content, and repeated measures of worker respiration. We observed a dose-dependent effect of both neonicotinoids on sucrose and protein consumption, with bees exposed to low doses consuming significantly less protein food, and greater amount of sucrose solution. A dose dependent effect was also observed in worker protein and lipid content, with bees having significantly less protein and more lipids when exposed to high doses of both pesticides. Both low and high doses, but not mid-level dose of imidacloprid resulted in greatly reduced worker respiration over time. Only the low dose of clothianidin significantly lowered bee respiration rate. Dose-dependent effect could reflect thresholds of honeybee physiological systems impacted by exposure to a range of doses of neonicotinoid pesticides. |
