Sub-Lethal Effects of Insecticides on Growth and Reproduction of Insects

Research on sub-lethal effects of pesticides has quickly grown to be an important part of entomology and ecotoxicology today. While acute toxicity leads to immediate death of the target pest, sub-lethal levels may cause changes to the pest's physiology, behaviour and reproduction (even though they won't necessarily result in immediate death). The physiological, behavioural and reproductive changes that occur from sub-lethal exposure can have impacts on population dynamics (emergence of new pests or re-emergence of previous problems) as well as on the stability of entire ecosystems. As part of this research, sub-lethal effects from two commonly used pesticides (imidacloprid and chlorantraniliprole) were investigated on the growth and reproductive characteristics of selected insect species, while keeping the insects under controlled laboratory conditions. When sub-lethal concentrations (LC₁₀ and LC₃₀) of imidacloprid and chlorantraniliprole were used for experimental exposure, larval development, pupal weight, adult longevity, reproductive output (fecundity) and egg viability (percentage of eggs hatched) were significantly impacted. Data indicated that both pesticide active ingredients resulted in longer times from larval development to pupation, less weight at pupation and greatly shortened adult life spans. Fecundity results varied by active ingredient and concentration, as some concentrations inhibited insect extraction while others increased it. These results are consistent with earlier studies, which have shown that sub-lethal exposure could depress or stimulate reproduction through hormetic responses. Sub-lethal exposure also has ecological consequences, such as pest re-establishment, changed predator-prey relationships, and disruption of biological controls. Sub-lethal effects have also been shown to negatively impact behavioral characteristics, including feeding, mating, and navigation. Ultimately, sub-lethal effects of insecticides significantly impact insect growth and reproductive fitness and should be considered in pest management strategies. Including evaluations for sub-lethal toxicity in regulatory policies may increase the sustainability and effectiveness of integrated pest management (IPM) programs.