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Increased susceptibility of the bertha armyworm, Mamestra configurata Walker, to Dipel, a commercial formulation of Bacillus thuringiensis (Berliner) ssp. kurstaki, indicated by low LC50 was observed when fourth instars were reared on artificial diet containing several lethal concentrations of B. thuringiensis ssp. Kurstaki supplemented with sublethal concentrations of 1,3,7-trimethylxanthine (caffeine), amidoindole 3-proprionic acid, theophylline 1,3-dimethylxanthine, or 3-isobutyl-1-methy lxanthine. Surviving treated larvae either gained no weight or lost weight after 7 d compared with controls which gained (mean ± SD) 235 ±35 mg per larva; the effect suggests cessation of feeding activity in treated larvae. The data showed that bertha armyworm larvae were weakly susceptible to commercial B. thuringiensis ssp. kurstaki alone applied to canola plants Brassica napus L. Caffeine at 0.1% wt/vol increased toxicity of the pathogen to the larvae 3.5-fold in artificial diet and 9.2-fold in a simulated field application on canola plants. Surviving larvae on the plants treated with B. thuringiensis ssp. kurstaki + caffeine gained 91± 59 mg per larva after 10 d, compared with 339 ±73 mg per larva on untreated plants. The construction and calibration of a spray chamber designed to apply known doses of microbial insecticides such as B. thuringiensis ssp. kurstaki to agricultural plants is described. We conclude that caffeine at 0.1% in B. thuringiensis ssp. kurstaki spray suspensions increases the toxicity of the microorganism and reduces feeding activity of bertha armyworm larvae on canola plants with little additional treatment cost.
Document Type: Research Article
Publication date: June 1, 1994
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Journal of Economic Entomology is published bimonthly in February, April, June, August, October, and December. The journal publishes articles on the economic significance of insects and is divided into the following sections: apiculture & social insects; arthropods in relation to plant disease; forum; insecticide resistance and resistance management; ecotoxicology; biological and microbial control; ecology and behavior; sampling and biostatistics; household and structural insects; medical entomology; molecular entomology; veterinary entomology; forest entomology; horticultural entomology; field and forage crops, and small grains; stored-product; commodity treatment and quarantine entomology; and plant resistance. In addition to research papers, Journal of Economic Entomology publishes Letters to the Editor, interpretive articles in a Forum section, Short Communications, Rapid Communications, and Book Reviews.