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Scientists Report on the Efficacy of a Binary Insecticidal Crystal Bt Protein for Corn Rootworms

June 21, 2002
In the most recent issue (June 2002) of the Journal of Economic Entomology (vol. 95, no. 3), scientists with Dow AgroSciences, in Indianapolis, Indiana, reported on the insecticidal effects of binary crystal proteins in laboratory bioassays against southern corn rootworm larvae. Southern corn rootworm colonies are often used in laboratory bioassays and are thought to serve as good test organisms that can be used to predict potential insecticidal effects against more important pests; in this case, western corn rootworms. The binary insecticidal protein discussed in the paper was produced from a strain (PS149B1) of Bacillus thuringiensis (Bt) and consists of two Cry proteins (Cry34Ab1-14kDa and Cry35Ab1-44kDa). The investigators report in the paper that both of these proteins have been co-expressed in transgenic corn plants and "effectively control" western corn rootworm grubs in the field. The authors further report that the smaller Cry protein (14kDa) was active against southern corn rootworms by itself; however, its activity was "synergized" by the larger Cry protein (44kDa).

Additional tests on these Cry proteins and others will surely follow, and the results will be of great interest to the agricultural community for many years to come. There is considerable anticipation on the part of producers regarding the potential commercialization of transgenic hybrids for corn rootworm management. In addition, interest in the reliability of seed treatments for rootworm management continues. During the next 5 years, a transition most likely will occur as producers lean more toward seed treatment and transgenic technologies, as the "backbone" of their rootworm management programs. Obviously a lot has to occur before this transition begins to take shape. Most notably, the U.S. EPA will need to approve the use of transgenic hybrids for corn rootworm control. In addition, to date, seed treatments have not shown that they provide consistent root protection against heavy corn rootworm infestations. I think systemic seed treatments have great potential; however, we still have much to learn.--Mike Gray

Author: Mike Gray

The Pest Management and Crop Development Bulletin
Executive Editor: Kevin Steffey, Extension Entomologist

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