Temperature-dependent, time-dose-effect model for pesticide effects on growing, herbivorous arthropods: Bioassays with dimethoate and cypermethrin

A toxicokinetics-based, temperature-dependent survival model for growing an imals with oral uptake of toxicants is used to analyze the results of two p esticide bioassays. With this approach, we aim at simultaneously addressing two complementary goals of pesticide bioassays, namely to assess species s ensitivity and to elucidate underlying mechanisms of toxic effects. As test organisms, newly hatched larvae of the chrysomelid beetle Gastrophysa poly goni L., dwelling on the underside of leaves of black bindweed Fallopia con volvulus (L.), kept at 12, 17, or 25 degrees C were used. Plants with larva e were sprayed with dimethoate and cypermethrin at five dosages and a contr ol. Survival was assessed during the following 6 d. The pesticide depositio n pattern on the plants and the overall concentrations in the plants were d etermined. For dimethoate, which is mainly taken up orally, observed surviv al curves could be simulated successfully by the model. In the case of cype rmethrin, which acts as a feeding deterrent, the model showed poor correspo ndence to the data. The significance of the results is discussed in relatio n to the test conditions and to toxicokinetics.