Mortality of first instars of Pieris brassicae (L.) and Agrotis segetum (Schiffermüller) exposed to crude destruxin extracts per os was analyzed by time-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 temporal course of mortality for both insects exposed to the different destruxins. Based on estimated LC50 and LT50 values, P. brassicae was much more susceptible to destruxins than A. segetum. Destruxin E seemed to be the most potent 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 destruxins against P. brassicae provide a basis for further investigations on destruxins as control agents against this insect. A. segetum larvae were only weakly susceptible to destruxins and the observed mortality of the larvae seemed to be a result of starvation caused by an antifeedant effect of the destruxins rather than by direct toxicity. Overall, the per os bioassays point toward a potential for possible future use of destruxins as control agent against lepidopteran pest larvae. The results do, however, also document, that the activity level of destruxins depends highly on the target insect species.
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