Submitted to: Pest Management Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 10/9/2006
Publication Date: 6/7/2007
Citation: Tarver, M.R., Shade, R.E., Shukle, R.H., Moar, W.J., Muir, W.M., Murdock, L.M., Pittendrigh, B.P. 2007. Pyramiding of insecticidal compounds for control of the cowpea bruchid (Callosobruchus maculates f.). Pest Management Science. Available at http://www3.interscience.wiley.com/cgi-bin/jhome/68504529?SRETRY=0. Interpretive Summary: Insect resistant crops are important as an economical and environmentally sound component of integrated pest management (IPM). However, the durability of single genes for resistance deployed in crop plants is often a concern. One strategy to enhance the durability of insect resistant crops is to use combinations or ‘pyramids’ of genes for resistance. However, the effectiveness of this strategy has rarely been experimentally tested. In this study we tested the effectiveness of combining different genes for resistance to provide ‘redundant killing’ (no insects survived with the combined genes for resistance). Results indicated that some combinations of genes for resistance were more effective than others in ensuring durable protection from pests. These results emphasize the joint action of genes for resistance cannot be predicted from separate results obtained for each gene and that some combinations of genes will greatly enhance the durable protection of crops from insect pests. Knowledge from this work will help scientists and breeders devise innovative methods to ensure more durable insect resistance in crops to prevent yield loss. The agricultural community (crop producers and commodity groups) will benefit from such durable resistance through increased yield and quality without increased cost.
Technical Abstract: The cowpea bruchid (Callosobruchus maculatus F.) (Chrysomelidae: Bruchini) is a major pest of stored cowpea grain. With limited technologies for managing the bruchid available, transgenic cowpeas with bruchid resistance genes engineered into them could become the next management tool. We investigated two different sets of potential transgenic insecticidal proteins using an artificial seed system. When CIP-PH-BT-J (Bt cry1A/1B) (0.1% or 1000 ppm) and recombinant egg white avidin (0.006% or 60 ppm) incorporated separately into artificial seeds caused 98.2% and 99% larval seed mortality rates respectively. Combining Bt cry1A/1B and avidin in the same seed provided redundant killing; no insects survived in seeds with the combined toxins. Similarly when avidin and wheat a-amylase inhibitor (aAI) (1% or 10000 ppm) incorporated separately into artificial seeds made with garden pea flour caused 99.8% and 98% mortality respectively. However, in combination avidin and aAI did not increase mortality, though there was a significant increase in developmental time. These results emphasize that the joint action of potential insecticidal compounds cannot be predicted from separate results obtained for each protein.