Effects of Bt maize on non-target lepidopteran pests

Abstract: Genetically modified (GM) maize with the insecticidal capacity of Bacillusthuringiensis, (Bt maize, expressing Cry1Ab) was first authorized in Spain in 1998. Since then itscultivated area has increased year by year to reach 78’000 ha in 2008, representing 21% of thetotal maize-growing area in Spain. In the study area (Lleida, Catalonia, NE Iberian Peninsula) itrepresents almost 80% of the total. Bt maize provides an effective control of two key lepidopteranpests, Sesamia nonagrioides (Lefèbvre) and Ostrinia nubilalis (Hübner). However, in addition tothe two corn borers, two other non-target Lepidoptera, Mythimna unipuncta (Haworth) andHelicoverpa armigera (Hübner), cause occasional but severe damage to maize. Effects of Btmaize on these two Lepidoptera were studied in laboratory and field trials. Some larvae of bothspecies can survive and complete development when feeding on Bt maize. Field evaluationscarried out from 2005 to 2008 showed no differences in the number of H. armigera larvae perplant between Bt and isogenic varieties in most of the trials. In the laboratory, M. unipunctashowed a larval survival of 15%, which is significantly lower than that recorded in isogenicvarieties. Additionally, larval development in survivors was significantly longer when they werefed Bt maize. Adults resulting from larvae developed on transgenic maize laid 13% fewer eggsthan those resulting from larvae developed on isogenic maize. When they had the choice, neonateM. unipuncta larvae preferred first Sorghum bicolor, then isogenic maize plants and finally Btplants for feeding. Recorded differential mortality caused by Bt maize on non-target Lepidopterain comparison with targeted corn borers may affect the composition and abundance of theLepidoptera community in maize as a consequence of Bt maize deployment.