Susceptibility of Microtheca ochroloma (Coleoptera: Chrysomelidae) to Botanical and Microbial Insecticide Formulations

Rammohan Balusu, Henry Y. Fadamiro

Abstract


The yellowmargined leaf beetle, Microtheca ochroloma Stål (Coleoptera: Chrysomelidae), is a key pest of organic crucifer production in the southern United States. The susceptibility of larvae and adults of M. ochroloma to some botanical and microbial insecticide formulations was evaluated using laboratory leaf-dip bioassays. Insecticides evaluated included OMRI (Organic Material Review Institute) approved formulations of PyGanic® (pyrethrum), Entrust® (spinosad), Mycotrol O® (Beauveria bassiana strain GHA), and NOFLY® (Isaria fumosoroseus strain FE 9901). Others were MBI-203 (experimental organic formulation of Chromobacterium subtsugae) and BotaniGard® 22WP (conventional formulation of Beauveria bassiana strain GHA). The insecticides were first evaluated at the field recommended rate against M. ochroloma larvae and adults, followed by multiple-concentration assays to determine the LC50 and LT50 for promising formulations. At the field recommended rates, all tested formulations were toxic to the larvae compared to the untreated control, whereas only Entrust® and PyGanic® were effective against the adults. Entrust® and PyGanic® caused 100% mortality to the larvae and adults after just 24 h of exposure. The LC50 values of Entrust® and PyGanic® were 200 × and 15 × less than the field recommended rates, respectively. MBI-203 was effective against the larvae (100% mortality after 5 days) but not against the adults. The entomopathogenic fungal formulations, Mycotrol®, NOFLY®, and BotaniGard®, were much less toxic with LT50 values of 10, 12, and 9 days, respectively. Although all 3 fungal formulations caused significantly higher larval mortality than the untreated control after 5 days of exposure, none resulted in more than 50% larval or 14% adult mortalities over the 9-day exposure period.

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