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Title: Increased Survival of Western Corn Rootworm on Transgenic Corn Within Three Generations of Onplant Greenhouse Selection

Author
item MEIHLS, LISA - UNIVERSITY OF MISSOURI
item Higdon, Matthew
item SIEGFRIED, BLAIR - UNIVERSITY OF NEBRASKA
item Miller, Nicholas
item Sappington, Thomas
item ELLERSIECK, MARK - UNIVERSITY OF MISSOURI
item SPENCER, TERRENCE - UNIVERSITY OF NEBRASKA
item Hibbard, Bruce

Submitted to: Proceedings of the National Academy of Sciences (PNAS)
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/17/2008
Publication Date: 12/2/2008
Citation: Meihls, L.N., Higdon, M.L., Siegfried, B.D., Miller, N.J., Sappington, T.W., Ellersieck, M.R., Spencer, T.A., Hibbard, B.E. 2008. Increased Survival of Western Corn Rootworm on Transgenic Corn Within Three Generations of Onplant Greenhouse Selection. Proceedings of the National Academy of Sciences. 105:19177-19182.

Interpretive Summary: Transgenic corn that controls the corn rootworm is a viable alternative to insecticides for managing the most economically important pests of corn. The agricultural industry has adopted a high dose/refuge strategy as a means of delaying the onset of insect resistance to transgenic crops, but the Bt corn products developed for corn rootworm control have been introduced with less than high-dose. We developed colonies of the western corn rootworm that survived the Bt product in the greenhouse along with an unselected colony. After three generations of full larval rearing on Bt corn, rootworm larvae survived equally on Bt and susceptible corn in greenhouse trials. In dose-response assays with the protein from the Bt corn on artificial diet, the dose of toxin required to kill half the population was 22-fold greater for the selected colony than the unselected colony. After six generations of greenhouse selection, larval recovery on Bt corn as a ratio of larval recovery on susceptible corn in the field was 11.7-fold greater for the selected colony than the unselected colony. Reciprocal crosses of the selected colony with the unselected colony suggest that several genes of small effect and multiple mechanisms are likely involved in conferring the observed resistance. The results suggest that rapid response to selection is possible in the absence of mating with unselected beetles, emphasizing the importance of effective refuges for resistance management. This information will be important to seed companies, the Environmental Protection Agency, and modelers in their attempts to develop resistance management plans for transgenic corn by providing more realistic assumptions in current mathematical models.

Technical Abstract: The agricultural industry has adopted a high dose/refuge strategy as a means of delaying the onset of insect resistance to transgenic crops. Recently, Bt corn products developed for control of western corn rootworm (WCR), Diabrotica virgifera virgifera, have been introduced with less than high-dose. Experience with insecticides has shown that exposure to sublethal doses can lead to a variety of resistance mechanisms. A greenhouse method of rearing WCR on MON863 transgenic corn (Zea mays L.) expressing the Cry3Bb1 protein was used in which ~25% of previously unexposed larvae survived relative to isoline survival (compared to 1 to 4% in the field). After three generations of full larval rearing on MON863 (Constant-exposure colony), WCR larvae survived equally on MON863 and isoline corn in greenhouse trials. In dose-response assays with Cry3Bb1 protein on artificial diet, the LC50 was 22-fold greater for the Constant-exposure colony than the Control colony. After six generations of greenhouse selection, the ratio of late instar larval recovery on Bt corn to survival on isoline corn in the field was 11.7-fold greater for the Constant-exposure colony than the Control colony. Reciprocal crosses of the Constant-exposure colony with the Control colony, and analyses of neutral genetic markers suggest that several genes of small effect and multiple mechanisms are likely involved in conferring the observed resistance. The results suggest that rapid response to selection is possible in the absence of mating with unselected beetles, emphasizing the importance of effective refuges for resistance management.