Laboratory bioassay assessing the enhancement of Cry3Aa toxicityto coleopteran storage pests – preliminary results

Abstract: Storage pests cause economic losses to stored grain worldwide. The traditional synthetic chemicals that have been used for their control are increasingly removed from the market because of increased regulatory constraints and insect resistance. The use of biopesticides based on Bacillus thuringiensis (Bt) spores offers a safe alternative but some storage pests show low sensitivity to any natural Cry toxin. Several recombinant proteins with N-/C-terminal and binding domain modifications of Cry3Aa were prepared in search for a derivative active on Tenebrio molitor and Tribolium castaneum (Coleoptera: Tenebrionidae). Test compounds were added to the standard larval diet and larval mortality was recorded in seven-day intervals for eight weeks of exposure. Probit analysis was used to estimate lethal effects of four doses of Cry3Aa and its derivatives and the LC50 was calculated. Slightly enhanced effects of some Cry3Aa derivatives in comparison with natural Cry3Aa toxin were detected.