Screening of the insecticidal activity of Bacillus thuringiensis strains against Lygus hesperus (Hemiptera: Miridae) nymphal population

Lygus hesperus Knight (Hemiptera: Miridae) is an economically important insect pest controlled primarily by chemical pesticides. Bacillus thuringiensis Berliner is a gram-positive bacterium that has been developed for the control of some insect pests in the orders Lepidoptera, Coleoptera, and Diptera. In this study, whole culture extracts of 94 B. thuringiensis strains from 83 serovars were added to an artificial diet and assayed against L. hesperus first and second instars. A total of five B. thuringiensis strains, B. thuringiensis variety thuringiensis, thuringiensis exotoxin +, morrisoni, tolworthi, and darmstadiensis generated > 98% mortality after 7 d of incubation. The screening was repeated with 117 alkali-solubilized trypsin-digested B. thuringiensis cultures and the same five B. thuringiensis strains showed nearly identical results. All five strains produce beta-exotoxin, which exhibits a wide host spectrum activity. No beta-exotoxin-minus B. thuringiensis strains showed significant toxicity against L. hesperus nymphs. The present work is one of the first thorough screenings of the wide diversity of the B. thuringiensis varieties for the control of L. hesperus nymphal populations.