|Zhu, Kun yan|
Submitted to: Journal of Economic Entomology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 5/10/2005
Publication Date: 8/1/2005
Citation: Li, H., Oppert, B.S., Higgins, R.A., Huang, F., Buschman, L.L., Zhu, K. 2005. Susceptibility of dipel-resistant and -susceptible Ostrinia nubilalis (Lepidoptera: Crambidae) to individual bacillus thuringiensis protoxins. Journal of Economic Entomology 98(4): 1333-1340. Interpretive Summary: Resistance to Bacillus thuringiensis by insect pests threatens the successful use of spray formulations and transgenic plants based on these bacterial toxins. Dipel-resistant and -susceptible strains of the European corn borer were tested for susceptibility to individual B. thuringiensis protoxins. Resistance ratios for each protoxin were considerably higher than the 40-fold resistance to Dipel. Resistance ratios based on mortality were higher than those based on growth inhibition. This information is useful to design new transgenic crops to control European corn borer damage, as well as to design effective resistance management strategies with spray formulations of B. thuringiensis.
Technical Abstract: Dipel-resistant and -susceptible strains of Ostrinia nubilalis Hübner were evaluated for larval mortality and growth inhibition on diets containing individual Bacillus thuringiensis protoxins. Resistance ratios for four of the Cry protoxins in Dipel (Cry1Aa, Cry1Ab, Cry1Ac, and Cry2Aa) were 170, 200, 510, and >640-fold, respectively, based on LC50s. These values were considerably higher than the 40-fold resistance to Dipel for this strain. The Dipel-resistant strain was 36-fold resistant to Cry1Ba, a protoxin not present in Dipel. Cry1Ca did not cause significant mortality for either resistant or susceptible larvae with doses as high as 1.0 mg/ml. Based on doses resulting in 50% growth inhibition (EC50), resistance ratios for Cry1Aa, Cry1Ab, Cry1Ac, and Cry2Aa, were 1.9, 3.0, 9.5, and 4.1-fold, respectively, which were lower than the resistance ratios calculated from LC50s. However, the resistance ratio of Cry1Ba was 20-fold based on the EC50. The differences in resistance ratios from larval mortality and growth inhibition bioassays may be associated with differences in bioassay methodology and/or in toxin responses due to physiological changes of Dipel-resistant O. nubilalis.