Agronomic and Environmental Impacts of Bt Cotton in Mexico

Worldwide cotton production was characterized by the highest pesticide input among the row crops. Mexico was not the exception, because at some point, cotton fields were sprayed with insecticides up to 18 times in a single crop season, most of them targeted to lepidopteran pests, and even with that intensive application regime, growers lost 30–50% of the potential yield, increased their production costs by 35%, mainly due to pests highly resistant to insecticides. With the availability of Bacillus thuringiensis’ Berliner (Bacillales: Bacillaceae) protein-expressing cotton (Bt cotton) in Mexico more than 20 yr ago, cotton’s pest management in the country has changed substantially. Growers use significantly less insecticide (50% less), and they are not worried about Pectinophora gossypiella (Saunders) (Lepidoptera: Gelechiidae) (pink bollworm) and Chloridea virescens (Fabricius) (Lepidoptera: Noctuidae) (tobacco budworm), pests that were extremely important at some point due to their negative impact on yields. The Helicoverpa zea (Boddie) (Lepidoptera: Noctuidae) (bollworm) populations, another limiting pest, are also no longer of concern, except in one small region of Mexico. Anthonomus grandis Boheman (Coleoptera: Curculionidae) (boll weevil), another very important pest, is not controlled by current Bt cotton cultivars, and binational eradication programs have been implemented in different regions of Mexico and the United States. In areas where A. grandis has not been eradicated but are currently within the eradication program, insecticide use has increased, because the goal is to disrupt the biological cycle of the pest using different techniques. Once the boll weevil eradication is achieved, it is expected that the use of insecticide will diminish, as has been the case in other now A. grandisfree areas. Currently, sucking insects such as Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae), Nezara viridula (Linnaeus) (Hemiptera: Pentatomidae), Lygus spp. Hahn (Hemiptera: Miridae), and Chlorochroa ligata (Hemiptera) (Say) (Hemiptera: Pentatomidae), for which current Bt cotton cultivars have no effect, are the ‘new’ pest problems of cotton production. Mexico is a unique example of the management of cotton pests. In order to continue as the world leader in cotton production per area, eradication programs for A. grandis and P. gossypiella have been successfully established, the latter supported by the high adoption of Bt cotton. These strategies that are part of an integrated pest management program have allowed insecticide use to be reduced by half, preserved the susceptibility to B. thuringiensis for more than two decades, and have continued to increase cotton yields for more than 20 yr.