Temperature-dependent, time-dose-effect model for pesticide effects on growing, herbivorous arthropods: Bioassays...

A toxicokinetics-based, temperature-dependent survival model for growing animals with oral uptake of toxicants is used to analyze the results of two pesticide bioassays. With this approach, we aim at simultaneously addressing two complementary goals of pesticide bioassays, namely to assess species sensitivity and to elucidate underlying mechanisms of toxic effects. As test organisms, newly hatched larvae of the chrysomelid beetle Gastrophysa polygoni L., dwelling on the underside of leaves of black bindweed Fallopia convolvulus (L.), kept at 12, 17, or 25°C were used. Plants with larvae were sprayed with dimethoate and cypermethrin at five dosages and a control. Survival was assessed during the following 6 d. The pesticide deposition pattern on the plants and the overall concentrations in the plants were determined. For dimethoate, which is mainly taken up orally, observed survival curves could be simulated successfully by the model. In the case of cypermethrin, which acts as a feeding deterrent, the model showed poor correspondence to the data. The significance of the results is discussed in relation to the test conditions and to toxicokinetics.