Topical applications of insecticidal proteins from Bacillus thuringiensis (Bt) have been used for nearly thirty years to successfully control certain insect pests. Bt proteins possess several characteristics which make them ideal insecticides; they are highly specific for certain insects and are safe to humans, animals, and many beneficial insects. Topical use of Bt is limited, however, by the high cost of production and short half life of these proteins. Genetic engineering techniques have facilitated the transfer of Bt genes into plants. Thus, the plant will produce the Bt protein encoded by the gene effectively overcoming the limitations of topical applications of this insecticide.

Several cotton lines transformed with Bt genes were field tested for their ability to control lepidopteran larvae. These lines were tested in a split plot fashion with the main plots being insecticide treatments (sprayed vs. unsprayed) and the sub plots being the line treatments. The sprayed treatments received weekly applications of insecticide for lepidopteran control while the unsprayed received no application of insecticide for lepidopteran control. In Starkville Mississippi, where the plots were artificially infested with Heliothis virescens, several Bt lines provided season long square and boll protection from these larvae. The level of control was equivalent to the control provided by weekly applications of insecticide. Yields were equivalent between the sprayed non transformed control and several unsprayed Bt lines. Severe damage occurred in the unsprayed, non transformed control (81% yield loss).

The other test locations (Tifton GA, Loxley AL, Bossier City LA, College Station TX, and Maricoua AZ) relied on natural infestations of lepidopteran pests. Across locations, several Bt lines provided lepidopteran control better than or equal to weekly applications of insecticide. This level of control also translated into yield protection. Thus, cotton plants genetically engineered to contain a Bt gene provide protection from damage by lepidopteran larvae which is at least equivalent to and often better than weekly applications of insecticides.