RELATIVE EFFECTS OF THE INSECTICIDE THIAMETHOXAM (ACTARA~(TM)) ON THE PREDATOR PODISUS NIGRISPINUS AND THE TOBACCO WHITEFLY IN NECTARIED AND NECTARILESS COTTON

摘要

The predaceous stinkbug Podisus nigrispinus (Heteroptera: Pentatomidae) feeds on plants as well as arthropod prey. Thus, the question arises whether feeding on plants might expose the predator to systemic insecticides via ingestion of the active ingredient or their metabolites through plant sap of treated plants. This interaction was investigated with nectaried and nectariless cotton plants cropped in pots and the systemic insecticide thiamethoxam at 0.5, 1 and 2 mg (AI) per plant. Developmental time of P. nigrispinus was extended and fresh adult body weight was reduced by feeding on prey and treated plants. Nymphs caged on treated plants with the highest thiamethoxam concentration at 15d after application produced only 13.2 percent of adults. However, females emerged from nymphs caged on plants and all thiamethoxam concentrations at day 30 after application presented similar reproductive characteristics, except for age of first oviposition, which was delayed on plants treated with the highest thiamethoxam concentration. Thiamethoxam at 0.5 mg (AI) per plant restrained tobacco whitefly, Bemisia tabaci colonization only during the first 15d after application for both cotton plants, and similar immature densities were sampled at day 35 after application on treated and untreated plants. On the other hand, treated plants with 1 and 2 mg (AI) per plant applied as a drench and cropped in pots were protected from tobacco whitefly for up to 45d of exposure to a whitefly colony.