Non‐targeted insecticidal stress in a pest species: insecticides, sexual fitness and hormesis in the Neotropical brown stink bug Euschistus heros

An understudied aspect of insecticides is their stress on non‐targeted pest species. Sublethal insecticidal stress may elicit a range of protective and non‐protective responses that may affect behaviour and sexual fitness of the exposed insects, which may lead to negative, neutral or stimulatory (i.e. hormetic) responses. We assessed the behavioural response of the Neotropical brown stink bug, Euschistus heros, a soybean pest in the Neotropical region with increasing pest status, following exposure to chlorantraniliprole, pyriproxyfen and spinosad, insecticides commonly used against soybean caterpillars and whiteflies. Both individuals, or only the male or female of each mating pair, were exposed. Reproductive behaviour and output were measured to determine insecticide‐ and gender‐mediated fitness. We found that treatment scenario significantly affected mating behaviour, and that the duration of some behaviours were significantly affected. Chlorantraniliprole and pyriproxyfen reduced latency to mate, while spinosad increased this behaviour. Insecticide exposure also decreased the interacting time of each couple and male antennation of the female. Fertility table analyses of exposed couples indicated negligible effect of pyriproxyfen exposure, while spinosad extended generation time and reduced net reproductive rate, leading to lower rates of population growth of the brown stink bug. In contrast, chlorantraniliprole led to only a slight extension on the generation time, but enhanced net reproductive rate of the stink bug leading to higher rates of population growth; no effects on sexual fitness were observed, as both compounds exhibited similar effect on females and males. Latency to mate correlated significantly with the population growth rate. The positive response to chlorantraniliprole exposure reinforces the notion that sublethal exposure of the brown stink bug to this insecticide may lead to stimulatory (hormetic) response favouring its outbreaks in soybean fields.