Non-targeted insecticidal stress on the Neotropical brown stink bug Euschistus heros

Abstract

Lethal and sublethal insecticide effects on non-targeted pest species are frequently neglected but have potential consequences for pest management and secondary pest outbreaks. Here, the lethal and demographic effects of four soybean insecticides (chlorantraniliprole, deltamethrin, pyriproxyfen, and spinosad, which are used against caterpillars, whiteflies, and green stink bugs) on the brown stink bug Euschistus heros (F.), the main stink bug species currently attacking Neotropical soybean fields, were assessed. Deltamethrin exhibited drastic acute mortality in adult females of E. heros with a median lethal time (LT50) of 0.6 days, whereas pyriproxyfen treated females exhibited a survival similar to that of water-treated insects (LT50 of 89 and 67 days, respectively). Chlorantraniliprole and spinosad-treated females exhibited intermediate survival with a TL50 of 54 and 47 days, respectively. Further scrutiny of the three most selective insecticides (i.e., chlorantraniliprole, pyriproxyfen, and spinosad) using age-structured matrices to assess the demographic impact of these compounds under earlier exposure indicated that both pyriproxyfen and spinosad significantly reduced the population growth of the pest species by compromising the survival of eggs (<17% hatching) and 1st nymphs (LT50 of 3 and 2 days, respectively) and fertility; these results were unlike those obtained for chlorantraniliprole- and water-treated controls, which exhibited less than 50% mortality during development. However, chlorantraniliprole significantly compromised the fertility of adult insects (>50% reduction compared with water-treated insects) to a greater extent than pyriproxyfen and spinosad, but without impairing insect population growth as much. Therefore, although pyriproxyfen and spinosad, besides deltamethrin, are not used to target the Neotropical brown stink bug, these insecticides adversely affected this pest species at the dose recommended for application on the label, thereby preventing its outbreak under such conditions.