Hormesis in insects: clarifying the dose-response and implications for beneficial insects

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Although it has long been appreciated that stress, when administered at moderate or high levels, can have deleterious effects on organisms, it is now clear that low levels of stressors, such as poisons, can actually stimulate biological processes. This phenomenon of inhibition of biological effects when a stressor is given at high doses, with stimulation when the organism is exposed to mild amounts of the stressor, is known as “hormesis”. In our studies on the hormesis phenomenon, we have repeatedly demonstrated that low doses of insecticide administered to insects can sharply increase population growth, increase weight of progeny, and alter expression of genes involved in stress responses and development. However, a number of basic and applied questions remain surrounding the hormetic response and insecticide-induced stimulations in insects. The principle long-term goals of the current research program are to better understand the nature of pesticide-induced hormesis in insects, and to demonstrate the occurrence and potential applications of the hormesis phenomenon for beneficial insects. Specifically, multiple highly qualified personnel will conduct experiments to test hypotheses to determine: (1) the molecular and biochemical mechanisms of pesticide-induced reproduction hormesis in insects; (2) the cause of pre-hormetic toxicity (i.e. hypersensitivity) observed in insects exposed to poisons below stimulatory (hormetic) concentrations; (3) whether mild levels of stress can be strategically applied to beneficial insect predators and parasitoids in order to boost their productivity for biological control; and (4) if exposure to low doses of pesticide can stimulate learning and reproduction in bees. The study of hormesis is rapidly increasing, but important gaps in our basic understanding of the phenomenon remain. The proposed research program will be highly original and will have high inter-disciplinary impact, melding questions of interest to researchers in toxicology, insect molecular biology, risk assessment, crop protection, and biological control. Using well-established insect-insecticide models, the research will discover the underlying molecular and biological mechanisms that give rise to observed hormetic dose-responses. Our proposed investigations into the causes of prehormetic toxicity are highly original and could be trailblazing for the field. The research will also probe questions surrounding the consequence of adaptive stress responses on biological fitness, an area of considerable debate among evolutionary biologists that study hormesis. At the same time, our research has important practical implications for agriculture and insect pest management. In agriculture, pesticide-induced stimulations of insect population growth have been reported. The resulting “pest resurgences” not only may result in increased crop/commodity damage, but may also lead to additional pesticide treatments, potentially exacerbating non-target impacts, insecticide resistance development, and environmental contamination. Thus, there are economic and environmental incentives to better understand the occurrence and consequences of pesticide-induced hormesis in insects. On the other hand, the potential implications of mild stress in stimulating development of beneficial insects (e.g. pollinators, natural enemies) have been largely ignored. As a consequence of our research, the biological control industry could realize significant benefits to its mass rearing production practices. Moreover, the demonstration of hormetic (stimulatory) responses in bees exposed to low doses of pesticide would be truly ground-breaking, and should give pause to those who assume that pesticide exposure always poses a risk to bees.