Resistance of Cotton Lines Containing a Bacillus thuringiensis Toxin to Pink Bollworm (Lepidoptera: Gelechiidae) and other Insects

Abstract

Three transgenic lines of cotton, Gossypium hirsutum L., carrying a modified insect-control protein from Bacillus thuringiensis subsp. kurstaki (Berliner), were evaluated for resistance to severallepidopterous insects. These three lines, along with the explant source cultivar, ‘Coker 312’, and a locally adapted control, ‘MD 51 ne’, were grown in a field experiment at Maricopa, Arizona. Early in the season, before bolls were available for infestation, the number of rosetted blooms caused by pink bollworm, Pectinophora gossypiella (Saunders), was 95% lower in the transgenic lines than in the control cultivars. The pink bollworm larvae penetrated bolls of the transgenic lines readily; however, live larvae recovered from incubated bolls, and percent seed damage were reduced 97-99% in the transgenic lines compared with the control cultivars. No live larvae were recovered from bolls of two transgenic lines, 62 and 65. The transgenic lines were highly resistant to cotton leaf perforator, Bucculatrix thurberiella Busck, as shown by an absence of larval populations and of leaf mining and feeding. The transgenic lines sustained very little leaf damage from saltmarsh caterpillar, Estigmene acrea (Drury), and beet armyworm, Spodoptera exigua (Hubner), whereas the control cultivars were almost defoliated by season’s end. As expected, the transgenic lines were not resistant to several nonlepidopterous insect pests, and they did not affect populations of beneficial insects. Higher populations of sweetpotato whitefly, Bemisia tabaci (Gennadius), on the transgenic lines than on the control cultivars may have been a consequence of reduced leaf feeding damage (by lepidopterous insects) rather than increased whitefly susceptibility of the transgenic lines. A breeding strategy to increase the insect resistance of cotton plants would be to combine the bacterial toxin trait with other resistance traits such as nectariless, okra leaf, and early maturity, known to reduce pink bollworm and other pest insects.