The occurence and mechanisms of hormesis in insects exposed to sublethal doses of insecticide

Since their inception, the toxicological sciences have generally been guided by the tenet that there is a dose-response threshold above which chemical exposures induce a biological effect, and below which none occurs. Although this principle has been a cornerstone of all facets of toxicology and has been invaluable for establishment of harmful exposure limits and effective doses of chemicals, there is now very strong support for the occurrence of hormesis, chemical response characterized by low-dose stimulation and high-dose inhibition of biological effects. Hormesis (after the Greek word 'to excite') has been documented for a wide range of organisms, endpoints and physical/chemical stressors, and has garnered interest from researchers in a variety of disciplines, mainly those who study human risk assessment and the biomedical sciences (e.g. oncology and the study of aging). However, the phenomenon has been less studied by scientists who examine effects of environmental toxins on invertebrate populations, particularly over the long term. Insects often display rapid and prolific reproduction, and are subject to exposure to a wide array of synthetic chemicals. This is especially true in agricultural settings where intense chemical inputs are commonplace. The proposed research will test hypotheses that exposure to toxic chemicals at low doses can have hormetic effects on insects. Numerous endpoints will be assessed to determine which display hormetic responses, and how these contribute to population growth stimulation. Experiments will determine dose-time-response relationships for individuals and across generations, and whether hormesis is consistent among different insect taxa and populations. Additional studies will elucidate the biochemical mechanisms for stimulated reproduction (e.g. elevated levels of metabolic enzymes) and examine properties of hormesis in chemical mixtures. These studies will advance our basic toxicological knowledge of the effects of low-dose chemical exposures on insects, with implications for environmental risk assessment, design of experiments to test hormesis, insect pest management and environmental toxicology.