Cecil H. Fox

Name of the game

The Pollyanna-like view ofBacillus thuringiensis (Bt) transgenic plants controlling pests reflected in the Research News article by Anne Simon Moffat (12 April, p. 211) belies past experience and present evidence. Chlorinated hydrocarbons, carbamates, organophosphates, pyrethroids, and other classes of chemicals have all been touted as panaceas for pest control. They were shortly found to be inadequate in most prophylactic applications because some individuals in the treated pest population had the genetic predisposition to be able to survive the treatment and the capacity to pass this capability on to their progeny. Transgenic Bt endotoxins will suffer the same fate if they are used to protect plant populations over wide areas. This and related genetic engineering technologies that rely on confrontational prophylactic tactics pose a significant threat to the stability of production agriculture for several reasons. First, resistance is inevitable. The continued effectiveness of the fermented Bt toxins over the past four decades has been primarily due to the limited applications made and the short residual activity they had after application. The surviving target pest population and other organisms in and around the treated area simply escaped the toxin, which primarily affects feeding lepidopterous larvae (more recently toxins effective against dipteran and coleopterous larvae have been developed), leaving susceptible adults, eggs, and pupae to survive and reproduce with the few, if any, larval survivors of the treatment. Incorporation of the Bt toxin in the tissues of tomatoes, cotton, corn, and other crops so that it is expressed from seedling to harvest and protected from ultraviolet degradation and weathering will largely eliminate escape and concentrate survivors in the crop. The rate at which resistance will develop into an economic problem depends mainly on the intensity of exposure. This is related to the crops incorporating the technology and the area over which they are used. If Bt toxins are simultaneously deployed against Helicoverpes in cotton, corn, and sorghum, I predict perhaps 25 to 75 generations (3 to 9 years) will elapse before resistance renders the technology useless. Second, resistance developed in response to transgenic Bt will transfer to fermented Bt products and render them useless against resistant pests. Third, currently effective conventional pesticides will perhaps be discontinued (because of decisions not to reregister, loss of market share, and other factors) and thus be unavailable in 3 to 9 years to prevent the epidemics of resistant pests that will ensue. Fourth, new or alternative technologies will not be on-line because the Bt transgenic plants will stifle competition. This impending disaster is preventable by more judicious deployment in time and space or by engineering the Bt transgenic plants to express the toxin in just the susceptible tissues during the briefperiods they are vulnerable to attack. This would suffice to prevent damage to the resource valued by humans and would allow the majority ofthe Bt-susceptible pest population to escape and breed with the few that are resistant. MARviN K. HARRIs Entomology Research Laboratory, Texas A&M University, College Station, TX 77843-2475