Predation of cotton bollworm by green lacewings in the presence of cotton aphid as alternative prey on transgenic Bt and conventional cotton

Abstract

Experiments were conducted in small arenas and on whole plants to explore the effect of cotton aphids, 'Aphis gossypii' Glover (Hemiptera: Aphididae), as alternative prey on the predation of 'Helicoverpa armigera' Hübner (Lepidoptera: Noctuidae) larvae by green lacewing larvae, 'Mallada signatus' Schneider (Neuroptera: Chrysopidae). Transgenic Bt (Bollgard II®) and conventional cotton plants were included to explore potential differences in the predator's performance on these cotton types. In small arenas, the presence of 20 aphids reduced predation on 'H. armigera' larvae by 22%(from 5.5 to 3.3 of 10) by a single lacewing larva over a 24-h period. The presence of 'H. armigera' reduced predation on aphids by ca. 29%(from 16.8 to 11.0 of 20) over 24 h. On whole plants, the presence of alternative prey had no effect on the number of 'H. armigera' larvae or aphids remaining after 3 days. The presence of 'H. armigera' larvae alone, without the predator, caused a 24% reduction in the numbers of aphids on conventional, but not on Bt cotton plants. The combination of Bt cotton and lacewing larvae caused a 96.6% removal of early-stage 'H. armigera' larvae, a statistically significant increase over the addition of the proportions (91.6%) removed by each factor measured separately, providing evidence of synergism. These studies suggest that the presence of aphids as alternative prey would not necessarily disrupt the predation by green lacewing on larvae of 'H. armigera', especially on Bt cotton.