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Title: Efficacy of Bacillus thuringiensis Cry3Aa protoxin and protease inhibitors toward coleopteran storage pests

Author
item Oppert, Brenda
item Morgan, Thomas
item KRAMER, KARL - Collaborator

Submitted to: Pest Management Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/26/2010
Publication Date: 5/1/2011
Citation: Oppert, B.S., Morgan, T.D., Kramer, K.J. 2011. Efficacy of Bacillus thuringiensis Cry3Aa protoxin and protease inhibitors toward coleopteran storage pests. Pest Management Science. 67(5):568-573. doi: http://dx.doi.org/10.1002/ps.2099.

Interpretive Summary: Environmental impacts and resistance to insecticides pose serious challenges to stored product pest control. In an effort to find new environmentally-friendly and effective control products for pests of stored products and grains, we evaluated the effect of bacterial toxins and digestive protease inhibitors on selected beetle storage pests. The yellow mealworm was most sensitive to the bacterial toxin, as has been demonstrated previously, but protease inhibitors had no effect on toxicity. We found that the bacterial toxin had little effect on the red flour beetle, with or without protease inhibitors. However, the bacterial toxin reduced the growth and increased mortality of the lesser grain borer, and these effects were increased with the addition of protease inhibitors. These data suggest that a combination of bacterial toxin and protease inhibitor may have application in the integrated pest management of the lesser grain borer.

Technical Abstract: Background: Environmental impacts and resistance to insecticides pose serious challenges to stored product pest control. Insect-resistant transgenic grain is a potential alternative to fumigants, but candidate control proteins are needed, especially for coleopterans. Therefore, we evaluated the efficacy of a coleopteran-active toxin, Bacillus thuringiensis Cry3Aa, in combination with or without protease inhibitors in laboratory feeding assays against coleopteran storage pests. Results: In a comparison of the toxicity of Cry3Aa protoxin towards three coleopteran storage pests, Tenebrio molitor was found to be most sensitive, Tribolium castaneum was most refractory, and Rhyzopertha dominica displayed an intermediate response. Cry3Aa combined with 3,500 ppm carboxypeptidase inhibitor or 5,000 ppm aprotinin resulted in both delayed development and increased mortality. Potato carboxypeptidase inhibitor and bovine aprotinin reduced the LC50 of Cry3Aa for R. dominica two- and three-fold, respectively. Cry3Aa treatment resulted in fewer progeny from R. dominica, and progeny was further reduced when the protoxin was combined with potato carboxypeptidase inhibitor. Conclusions: These data support the hypothesis that a combination of Cry3Aa protoxin and protease inhibitors, particularly a potato carboxypeptidase inhibitor, may have applications in control strategies for preventing damage to stored products and grains caused by coleopteran pests.