Acute toxicity and duration of harmful activity of nine insecticides on Trichogramma pretiosum, a parasitoid used in augmented biological control of Helicoverpa spp. in Brazilian soybean fields

Abstract

Combining biological and chemical control is essential for implementing Integrated Pest Management programs. In soybean crop, one way to integrate these control tactics for managing Lepidoptera pests, such as Helicoverpa armigera Hübner (Lepidoptera: Noctuidae) is by releasing parasitoids to control moth’s eggs, and spray chemical pesticides to control caterpillars. However, it is necessary to know if these tactics can be combined, with no harm to their individual performances. Therefore, this study evaluated lethal and sublethal effects on Trichogramma pretiosum Riley (Hymenoptera: Trichogrammatidae) following exposure to nine insecticides commonly used in soybean. First, adults were exposed to insecticide residues on leaf disks immediately after spraying and acute toxicity was assayed 24 h after exposure. Surviving insects, as well as their progeny, were evaluated for sublethal effects, such as reduction in parasitism, longevity and flight capacity. In a second bioassay, leaf disks were cut from greenhouse-grown plants 3, 7, 10, 17, 24 and 31 days after insecticide application. Adults were again exposed to leaf disks for 24 h, and then allowed to parasitize host eggs for 24 h, and progeny survival to emergence was recorded. Chlorantraniliprole and indoxacarb were the safest pesticides, with low acute toxicity and no sublethal effects, and therefore can be considered compatible with releases of T. pretiosum. Methoxyfenozide, teflubenzuron and flubendiamide also lacked any acute toxicity, but reduced either female longevity, or the longevity of their offspring. Acephate and chlorpyriphos both caused >85% wasp mortality, whereas lambda-cyhalothrin + thiamethoxam and chlorfenapyr had the greatest residual activity, causing high mortality and many sublethal effects. Therefore, these products cannot be used associated with releases of the parasitoid in IPM programs.