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Abstract
The main objective of this study was to assess the susceptibility of the black cutworm (Agrotis ipsilon) to the biopesticide spinosad and to a commercial formulation (GHA strain) of the entomopathogenic fungus, Beauveria bassiana. Secondly, we quantified the effects of sublethal doses of spinosad on a number of A. ipsilon fitness parameters, and interactions resulting from simultaneous applications of sub-lethal doses of spinosad and B. bassiana. Under laboratory conditions, A. ipsilon third instar larvae were highly susceptible to spinosad, with an estimated LC50 of 50 ppm. The entomopathogenic fungus, B. bassiana had a lower efficacy with an estimated LC50 of 7×107 spores mL−1. Topical applications of 5, 7.5 and 10 ppm of spinosad on third instar larvae reduced larval size and increased time to pupation and to emergence. However, pupal and adult weights were not significantly different between treated and control individuals. Additivity was observed from most spinosad–B. bassiana combinations tested, thus indicating compatibility between products. We concluded that spinosad is a promising tool for controlling black cutworm larvae alone or in combination with other products.
Acknowledgements
The authors thank N. Bostanian for comments on a earlier version of the manuscript; Y. Fournier, N. Dauphinais, É. Taschereau, N. Turgeon, S. Campagnoro, J. Roy, É. Hamon and É. Messier for dedicated technical assistance; and S. Daigle for statistical advice. The Natural Sciences and Engineering Research Council of Canada, the Canadian Golf Course Superintendents Association, The Coalition for Responsible Golf and the Canadian Turfgrass Research Foundation provided financial support for this project.