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

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 Helico- verpa armigera Hubner (Lepidoptera: Noctuidae) larvae by green lacewing larvae, Mallada signatus Schneider (Neuroptera: Chrysopidae). Transgenic Bt (Bollgard II ® ) and conventional cotton plants wereincluded toexplorepotentialdifferencesinthepredator'sperformanceonthesecottontypes. In smallarenas, thepresence of20aphidsreduced predationonH. armigeralarvaeby 22% (from5.5 to 3.3 of 10) by a single lacewing larva over a 24-h period. The presence of H. armigera reduced preda- tion onaphids byca. 29% (from 16.8to 11.0of20) over24 h.On whole plants,the presenceofalter- native 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 theaddition ofthe proportions (91.6%) removed by each factor measured separately,providing evidence ofsynergism.Thesestudies suggestthat the presenceofaphidsas alternativepreywouldnot necessarilydisruptthepredationbygreenlacewingonlarvae ofH. armigera, especially onBt cotton.