Long-term regional suppression of pink bollworm byBacillus thuringiensiscotton

Abstract

Despite the potentially profound impact of genetically modified crops on agriculture and the environment, we know little about their long-term effects. Transgenic crops that produce toxins from Bacillus thuringiensis (Bt) to control insects are grown widely, but rapid evolution of resistance by pests could nullify their benefits. Here, we present theoretical analyses showing that long-term suppression of pest populations is governed by interactions among reproductive rate, dispersal propensity, and regional abundance of a Bt crop. Supporting this theory, a 10-year study in 15 regions across Arizona shows that Bt cotton suppressed a major pest, pink bollworm (Pectinophora gossypiella), independent of demographic effects of weather and variation among regions. Pink bollworm population density declined only in regions where Bt cotton was abundant. Such long-term suppression has not been observed with insecticide sprays, showing that transgenic crops open new avenues for pest control. The debate about putative benefits of Bt crops has focused primarily on short-term decreases in insecticide use. The present findings suggest that long-term regional pest suppression after deployment of Bt crops may also contribute to reducing the need for insecticide sprays.G enetically engineered crops have quickly become a significant component of agriculture, but little is known about their long-term consequences. Transgenic cultivars of cotton and maize that produce toxins from Bacillus thuringiensis (Bt) to control insect pests were grown on 12 million hectares worldwide during 2001 (1). A major concern is that rapid evolution of resistance by pests could nullify the benefits of Bt crops (2-6). It has also been proposed, however, that Bt crops imposing high mortality could cause regional suppression of target pests before resistance occurs (6-9). This would be most likely for target pests with a narrow host range, because their diet would be affected most by Bt crops. Here we report results of a large-scale 10-year study revealing that extensive use of Bt cotton in Arizona caused regional suppression of pink bollworm (Pectinophora gossypiella), an ecological specialist on cotton (10).Pink bollworm moths emerge in the spring, and four to five generations are completed before winter diapause begins (10). Population growth is exponential in non-Bt cotton fields where the pink bollworm is virtually always present. Survival of pink bollworm larvae is Ͻ0.5% in Bt cotton fields (3). We hypothesized that regional declines in pink bollworm density would occur because deployment of Bt cotton reduces the number of source habitats (non-Bt cotton fields) and the net reproductive rate of migrants from source habitats. Accordingly, we expected a density decline in regions where a threshold use of Bt cotton was exceeded (Fig. 1). To test this hypothesis, we evaluated changes in pink bollworm population density related to abundance of Bt cotton in each of 15 cotton-growing regions in Arizona during the 5 years before and the 5 years after deploym...

Delayed resistance to transgenic cotton in pink bollworm

“…Also, despite a widely publicized, grower-sponsored hotline and rapid response team for addressing potential resistance problems (35), no cases of reduced efficacy related to resistance have been documented. Consistent with the lack of field-evolved resistance, long-term suppression of pink bollworm has occurred in regions of Arizona with high adoption of Bt cotton (36).…”

Resistance to a Bacterial Toxin Is Mediated by Removal of a Conserved Glycosylation Pathway Required for Toxin-Host Interactions

“…Thus insects may be less able to tolerate loss of function of this pathway. Perhaps this is part of the reason for the high efficacy of insecticidal Cry toxins even over long periods of selection (26). However, viable/sterile mutant alleles of egh and brn exist.…”

Frequency and fitness cost of resistance to Bacillus thuringiensis in Chrysomela tremulae (Coleoptera: Chrysomelidae)

“…Transgenic plants producing Bacillus thuringiensis (Bt) toxins to control their key pests provide an attractive alternative to conventional insecticide sprays (Shelton et al, 2002;Carrière et al, 2003). One of the main risks associated with the widespread use of these plants is rapid adaptation of the pest targeted by the toxins (Gould, 1998).…”