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Bacillus thuringiensis var israelensisδ-endotoxin protein active against mosquitoes was inactivated by prior incubation with lipids extracted from Aedes albopictuscells. Experiments with lipid dispersions and multilamellar liposomes showed that the toxin binds to phosphatidyl choline, sphingomyelin and phosphatidyl ethanolamine provided these lipids contain unsaturated fatty acids. Phosphatidyl serine binds toxin less efficiently and phosphatidyl inositol, cardiolipin, cerebroside and cholesterol show no affinity for the toxin. The results suggest an insecticidal mechanism in which interaction of toxin with specific plasma membrane lipids causes a detergent-like rearrangement of the lipids, leading to disruption of membrane integrity and eventual cytolysis.

The two δ-endotoxins comprising the Bacillus thuringiensisvar. kurstakiHD1 insecticidal protein crystal were separated. The lepidopteran-specific protoxin was activated in vitro and its mechanism of action investigated. Toxicity towards Choristoneura fumiferanaCF1 cells was specifically inhibited by preincubation of the toxin with N-acetylgalactosamine and N-acetylneuraminic acid. The lectins soybean agglutinin and wheat germ agglutinin, which bind N-acetylgalactosamine, also inhibited toxicity. Since N-acetylneuraminic acid is not known to occur in insects, these results suggest that the toxin may recognise a specific plasma membrane glycoconjugate receptor with a terminal N-acetylgalactosamine residue.