Comparing the foraging behaviour of green lacewing larvae ('Mallada signata') on transgenic Bt cotton and conventional cotton using 'Helicoverpa armigera' eggs or neonate larvae and cotton aphids ('Aphis gossypii') as prey

Abstract

We investigated whether the transgenic Bt cotton influenced the foraging behaviour of a generalist predator (green lacewing larvae: 'Mallada signata' Neuroptera: Chrysopidae) on 'Helicoverpa armigera' eggs or neonate larvae in presence of aphid ('Aphis gossypii' Homoptera: aphididae). Experiments were conducted on whole single plants in cabinets or greenhouse cubicles with control over environmental variables at the University of New England, Armidale, Australia. Bt and conventional cotton plants were infested with aphid nymphs or 'H. armigera' (eggs or larvae) or both. In treatments with lacewings, two 4-day old lacewing larvae were released onto each plant. Observations of lacewing activity (resting, searching or feeding) and position (upper side of leaf, lower side of leaf, stem, petiole, square, flower or boll) were recorded over three periods (morning, noon and afternoon) each day for three consecutive days using a laptop computer (Noldus R software Wageningen University, The Netherlands). In all cases green lacewing larvae spent the largest portion of their time on the lower surface of leaves (26-60%) followed by fruit buds (cotton squares) (20-22%). In growth cabinet experiments searching was the most common activity (53%) followed by resting (40%) and feeding (7%), however, in green house cubicles, resting was the most common activity (68%) followed by searching (27%) and feeding (5%). But there was no significant difference in activity between transgenic Bt or conventional cottons in these studies. Overall, Bt cotton plants exerted no significant effect on the foraging behaviour of green lacewing.