Relative abundance and damage by target and non-target insects on Bollgard and BollgardII cotton cultivars

Bollgard® and BollgardII® cotton cultivars were evaluated for their efficacy for control of bollworms and their effects on sucking insects and the abundance of natural enemies under bollworm insecticide protected and non-insecticide protected field conditions during the 2004 and 2005 cropping seasons. Bollgard cultivars are genetic transforms that produce Cry1Ac toxins from Bacillus thuringiensis (Bt) to control American bollworm, Helicoverpa armigera. Second generation BollgardII cultivars contain 2 toxins, Cry1Ac and Cry2Ab, and are more effective in controlling a broader range of caterpillar species. Bollgard cultivars were free of H. armigera damage until harvest under insecticide protected as well as non-protected conditions. Both BollgardII and Bollgard cultivars were infested with larvae of spotted bollworm, Earias vitella, and spiny bollworm, Earias insulana, at later crop growth stages. Neither BollgardII nor Bollgard cultivars were free of square (fruiting body), open boll and loculi damage. Bollworm damage did not reach economic threshold levels up to harvest. Densities of sucking insects (Amrasca biguttula biguttula, Bemisia tabaci, Aphis gossypi, and Thrips tabaci), of the foliage feeder Myllocerus undecimpustulatus and of predators (Chrysoperla spp., Orius spp., Coccinella spp., Brumus spp., Vespa spp., Lycosa spp., and Aranews spp.) were similar on Bollgard, BollgardII and conventional cultivars. The time of the first appearance of bollworms, sucking insects and predators on Bt cotton did not vary from conventional cotton varieties. Insecticidal protection based on economic threshold levels resulted in significant reductions in bollworm damage on conventional cultivars.