AN EXAMINATION OF IMIDACLOPRID INDUCED STRESS AND HORMESIS IN THE BENEFICIAL INSECT PREDATOR, PODISUS MACULIVENTRIS (SAY) (HEMIPTERA: PENTATOMIDAE)

Abstract

Traditional models of toxicology have failed to capture the biological complexity of low dose effects of toxicological agents on organisms and the environment. The hormetic model, whereby low dose exposures to chemical or other stressors stimulate biological processes, has been shown to be a common occurrence in the toxicological literature. Stimulatory effects on life-history traits such as growth, reproduction, longevity, survival, and increased stress tolerance occur across the biological spectrum and are ubiquitous in insects. I examined the effects of low doses of imidacloprid on the beneficial insect predator, Podisus maculiventris, on survival and reproductive traits in insects exposed as nymphs or adults, and subsequent effects across generations. I also examined whether the same concentrations could induce hormesis on predatory behavior and predation. Finally, I further explored how hormesis manifests in insects at the molecular level through a systematic literature review and through a more specific transcriptome analysis of P. maculiventris. I observed that reproduction may be stimulated in P. maculiventris, without major effects on behavior and predation, but effects vary with age, generation, sex, and bioassay design. Molecular responses associated with hormesis included changes in the expression of genes associated with DNA damage response and repair, antioxidantion, detoxification, and growth, development, and reproduction. Further, analysis of the literature revealed that while patterns in the molecular responses associated with hormesis are robust, coordination of molecular responses is influenced by such things as stressor, life stage, time and generation, and sex of the individual. Thus, establishing stress response profiles may be necessary to determine the overall mechanism of hormesis.