for Bt cotton (Mullin and Mills 1999), which led to an estimated reduction of over 5 million acre-treatments and over 2 million pounds of chemical insecticide (Gianessi and Carpenter 1999). However, estimated benefits might depend on the baseline level of pest infestation during a specific growing season and on the techniques used to make comparisons (USDA 1999d). The use of transgenic pest-protected crops has been profitable in growing regions subject to severe pressure from specific pests or where alternative means of pest control have been infeasible or expensive. For example, Bt cotton has been accepted by a large percentage of growers in states where pest resistance to synthetic pyrethroids has left them without chemical means of controlling bollworms, but limited in other regions where pest hazards are not so extreme (USDA 1999d; Falck-Zepeda et al. 1999). Adoption of Bt corn has similarly been limited to areas with the highest pest pressure (USDA 1999d).

In addition to the approved commercial transgenic crop varieties, thousands of transgenic varieties are undergoing field trials (USDA 1999c). From 1987 through January 2000, the number of permits issued and notifications acknowledged was over 6700; about 3000 were for varieties having pest-resistance genes (table 1.5).

1.6 PUBLIC CONCERNS AND ISSUES

Given the rapid increase in acres planted with commercial transgenic crops and the likely additional increase in their use, many groups have raised concerns about the ecological and human health risks that might be posed by these crops (Ho 1998). Although the risks might not, in principle, differ in type from those associated with other products (for example, conventional pest-protected plants, pesticides), the public has focused its attention on transgenic crops.

Concerns over pesticidal traits include the enhanced evolution of resistant pest strains, the toxicity or allergenicity of the gene products to

TABLE 1.5 Number of Permits Issued for or Notifications of Field Trials in the United States Involving Crops with Pest-Resistance Genes, 1987-1999.

Category of Resistance

Number (% of all field trials)

Insect

1505 (22)

Virus

1013 (15)

Fungal

378 (5.5)

Bacterial

78 (1.2)

Nematode

7 (0.1)



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