Controlling Cotton Pests

Letters from: [ W. Randy Deaton ][1] [ Marvin K. Harris ][1] [ J. R. Bradley Jr. ][1] Contrary to the characterization in Jocelyn Kaiser's article “Pests overwhelm Bt cotton crop” (News & Comment, [26 July, p. 423][2]), the Bollgard Bacillus thuringiensis ( Bt ) gene by Monsanto is providing economic and environmental benefits to cotton growers and is performing as expected given this year's severe pest conditions. Bollgard was evaluated in 6 years of field tests before commercialization. The vast majority of these tests were done in full public view by scientists at the U.S. Department of Agriculture, universities, and extension facilities. Control of the pests targeted for this product—tobacco budworm, pink bollworm, and bollworm—was excellent. In a few of the field tests, high infestation levels have required application of pesticides to supplement the control provided by the Bt gene. Monsanto is well aware of the potential for pests to adapt to the Bt protein. Because we—along with many others—have much to lose if this happens, we have worked long and hard with resistance management experts to develop strategies to delay the onset of resistance. Strategies vary depending on the insect involved. With the bollworm, the key strategy is refugia, host plants where the insect can escape exposure to the Bt protein. Nonselected populations that develop on these refuges help dilute and suppress any resistance genes that may develop in the Bollgard fields. The bollworm has a multitude of hosts—both wild and crop plants. With Bollgard, resistance management is taken even further by requiring growers to plant refuges with cotton that does not contain the Bollgard gene. When both the natural and mandated refuges are combined, resistance development in the bollworm can be delayed significantly. # {#article-title-2} The bollworm outbreak on Bt cotton is not a manifestation of physiological resistance predicted in 1991 ([1][3]); rather, the epidemic apparently arises from extant populations that have the inherent ability to discriminate among tissues with varying concentrations of the toxin within a plant. Whereas physiological resistance in insects to pesticides and plant resistance (biotypes) is well documented ([2][4]), inherent behavioral capabilities of insects to discriminate in a toxin mosaic superimposed on their host or habitat is not well understood ([3][5]). Insect-resistant transgenic plants appear to provide an ideal substrate in which entomologists can explore this previously recalcitrant and otherwise neglected subject. Nonlethal repellency of preadapted populations from human-valued resource tissues to yield insensitive tissues offers the prospect of conserving the extant insect genome by these intraplant refugia and of increasing mortality in cannibalistic species by concentrating populations in smaller areas. Realization of such possibilities would be accelerated if prepared minds were combined with proprietary technology in a context of production agriculture. 1. 1.[↵][6] 1. M. K. Harris , Science 253, 1075 (1991). [OpenUrl][7][CrossRef][8][PubMed][9][Web of Science][10] 2. 2.[↵][11] 1. R. L. Metcalf, 2. R. A. Metcalf , Destructive and Useful Insects McGraw-Hill New York 1993 7.42 7.47; Biology and Breeding for Resistance M. Harris, Ed. (Texas Department of Agriculture Commission, Texas A&M University, College Station, TX, 1980). 3. 3.[↵][12] 1. A. Brown, 2. J. Haworth, 3. A. Zahar , J. Med. Entomol. 13, 4 (1976). [OpenUrl][13] # {#article-title-3} It is regrettable, but not surprising, that Bt cotton in its initial year of commercialization has fallen victim to the bollworm. During 1994, when bollworm numbers were extremely high in North Carolina, peak boll damage and yield reductions in two of our Bt cotton tests exceeded 20% ([1][3]). Our data ([1][3], [2][4]) were summarily ignored in favor of data acquired when there were low numbers of “wild” bollworms or from test sites artificially infested with laboratory-cultured larvae. The wave of euphoria created by Bt cotton swept across the cottonbelt and carried many entomologists with it. In Bt cotton, biotechnology has provided cotton farmers with a most powerful tool to assist in the management of insect pests; however, for success and sustainability the tool must be strategically integrated with other management tactics into systems designed for specific areas. 1. 1. 1. J. S. Mahaffey, 2. J. R. Bradley Jr., 3. J. W. Van Duyn , Proc. 1995 Beltwide Cotton Conf. 2, 795 (1995). [OpenUrl][14] 2. 2. 1. J. S. Mahaffey, 2. J. S. Bacheler, 3. J. R. Bradley Jr., 4. J. W. Van Duyn , Proc. 1994 Beltwide Cotton Conf. 2, 1061 (1994); [OpenUrl][15] 1. A. L. Lambert, 2. J. R. Bradley Jr., 3. J. W. Van Duyn , Proc. 1996 Beltwide Cotton Conf. 1, 931 (1996). 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