ABSTRACT

Transgenic cottons expressing either one or two Bacillus thuringiensis (B. t.) Berliner proteins, along with the conventional sister line, were evaluated in four 2002 field experiments with regard to impact on bollworm production in North Carolina. The relative numbers of bollworms that were capable of successfully completing development on conventional, Bollgard®, and Bollgard II® cottons under insecticide-sprayed and unsprayed conditions were estimated. Bollgard and Bollgard II genotypes reduced bollworm larvae, pupae, and damaged bolls produced per acre as compared to the conventional variety; the Bollgard II genotype further reduced the numbers of bollworm larvae, pupae, and damaged bolls per acre below that of the commercial Bollgard variety. Utilization of an insecticide application for bollworm control also significantly reduced numbers of bollworm larvae, pupae, and damaged bolls produced per acre as compared to untreated genotypes. With regard to per acre adult production, insecticide-treated Bollgard and Bollgard II cottons, along with untreated Bollgard II cottons, successfully reduced numbers of adults when compared to pyrethroid-treated and untreated conventional cotton and untreated Bollgard cottons. However, application of insecticides to Bollgard II cottons offers the most effective B. t. resistance management strategy for bollworm.