Side-effects of indoxacarb and lufenuron on Trichogramma brassicae Bezdenko (Hymenoptera: Trichogrammatidae) under laboratory conditions

This research was carried out to investigate lethal and sublethal effects of commercial formulations of indoxacarb and lufenuron on survival, development and parasitism of Trichogramma brassicae Bezdenko under laboratory conditions (25±2 °C, 60±5% RH, and 16:8 h L: D). Each insecticide was applied at four concenterations including 1000, 750, 500, and 250 ppm (i.e. at recommended field application rate and three lower concenterations) and their effects were studied through three exposure methods, including contaminating adult’s food (honey solution 10%) with insecticides, residual contact, and dipping parasitized host eggs (in pre-pupa stage of parasitoid) in insecticide solutions. The results showed that both insecticides significantly increased adults’ mortality and decreased their longevity, fecundity, and emergence rate in comparison to control, and these adverse effects, increased with increasing applied concenteration. The highest mortality (52.5±6 percent), shortest longevity (1.72±0.1 days), and lowest parasitism rate (14.7±0.97 percent) were observed in those parasitoids that fed on solution contaminated with indoxacarb 1000 ppm. Dipping parasitized host eggs in recommended field rates of indoxacarb and lufenuron adversely affected prepupa survival, and reduced adult emergence by 19.7 and 19.3%, respectively. According to the IOBC categories of toxicity, both insecticides were found to be "slightly harmful" when they ingested through contaminated honey solution, and "harmless" when adult parasitoids exposed to their residuals and prepupae dipped in their solutions. Therefore, these insecticides are recommended as nearly safe products in biological control programs of lepidopteran pests with T. brassicae.