Time-concentration mortality of Pieris brassicae (Lepidoptera : Pieridae) and Agrotis segetum (Lepidoptera : Noctuidae) larvae from different destruxins

Mortality of first instars of Pieris brassicae (L.) and Agrotis segetum (Sc hiffermuller) exposed to crude destruxin extracts per os was analyzed by ti me-concentration-mortality regressions based on the complementary log-log ( CLL) model, and was compared with the mortality from pure destruxins A and E and the synthetic analog hpy-6 destruxin E. The model described the tempo ral course of mortality for both insects exposed to the different destruxin s. Based on estimated LC50 and LT50 values, P. brassicae was much more susc eptible to destruxins than A. segetum. Destruxin E seemed to be the most po tent against P. brassicae, followed by the synthetic analog hpy-6 destruxin E, and destruxin A was least active. The results of the toxicity of pure d estruxins against P. brassicae provide a basis for further investigations o n destruxins as control agents against this insect. A. segetum larvae were only weakly susceptible to destruxins and the observed mortality of the lar vae seemed to be a result of starvation caused by an antifeedant effect of the destruxins rather than by direct toxicity. Overall, the per os bioassay s point toward a potential for possible future use of destruxins as control agent against lepidopteran pest larvae. The results do, however, also docu ment, that the activity level of destruxins depends highly on the target in sect species.