Impact of biopesticides on feeding and mortality of adult spotted cucumber beetle (Diabrotica undecimpunctata howardi) in laboratory assays

The spotted cucumber beetle, Diabrotica undecimpunctata howardi, is a serious pest of field and vegetable crops. Adult beetles feed on leaves, stems, and fruit of melons, and may vector bacterial wilt disease caused by Erwinia tracheiphila. Spotted cucumber beetles are difficult to manage without the use of broad spectrum or systemic pesticides. The investigation of biorational products based on naturally occurring organisms for management of cucumber beetles is warranted by the increase in demand for organic produce and for resistance management. We examined the efficacy of a novel biopesticide, MBI-203 (Marrone Bio Innovations, Davis, CA), Mycotrol O (Beauveria bassiana strain GHA, Laverlam, International Corporation), and two strains of entomopathogenic fungi Isaria fumosorosea (Ifr 3581 and 1506) on feeding inhibition and mortality of spotted cucumber beetles on Galia melon (Cucumis melo var. reticulatus) leaf discs in laboratory bioassays. Applications of MBI-203 and Mycotrol O resulted in reduced feeding by adult beetles, but did not influence mortality in 4 day assays. Applications of Ifr 3581 and 1506 at the 10⁷ spore concentrations did not impact beetle feeding or mortality in 7 day assays compared to sterile water sprays. Beetle cadavers were saved to determine mycosis. For Ifr strain 3581, 39% of beetle cadavers exposed were mycosed. Feeding inhibition by MBI-203 and Mycotrol O may help protect melon crops from cucumber beetle damage; and although Ifr strain 3581 can infect adult cucumber beetles, the strains tested do not reduce feeding or survival in the laboratory thus far.