Comparative toxicity and binding of Bacillus thuringiensis Cry1 toxins to Asian and European corn borers (Lepidoptera: Crambidae)

Transgenic Bacillus thuringiensis (Bt) corn is extremely effective against the European corn borer (ECB), Ostrinia nubilalis (Hübner) and its sibling species, the Asian corn borer (ACB), Ostrinia furnacalis (Guenée). An enormous amount of information has been generated on this technology as it relates to the ECB. To determine whether this information can be leveraged for decisions regarding the use of transgenic corn against the ACB, experiments were designed: 1) to determine whether the pattern of sensitivity to various Bt Cry1 toxins is similar between the two species and 2) to compare binding patterns and expression of putative toxin receptors. Test insects included laboratory-reared ACB originating from Malaysia, a susceptible lab colony of ECB maintained at the University of Nebraska-Lincoln and a negative control consisting of the sugarcane borer (SCB), Diatraea saccaralis (Fabricius) from Louisiana which represents a different genus from the same family. Bt toxins tested included Cry1Aa, Cry1Ab, Cry1Ac, Cry1Ba and Cry1F. Bioassay results showed that both corn borer species exhibited similar sensitivity to all toxins suggesting shared toxin receptors and mechanisms of toxicity for both species. SCB showed similar sensitivity to Cry1A toxins but the susceptibility to Cry1Ba and Cry1F was inversely related to the two corn borer species. Immunoblots using brush border membrane vesicle preparations from midgut tissues revealed that both ACB and ECB shared a common receptor that binds to Cry1Ab toxin which also exhibited comparable expression of putative cadherin-, aminopeptidase-N- and alkaline phosphatase-like receptors. These results support the similarity of ACB and ECB susceptibility to Bt Cry1 toxins.