Monitoring of pest and beneficial insect populations in summer sown Bt maize

During 2002 in Sardinia, field studies were conducted in a summer sown cultivation of transgenic corn, expressing the Cry1Ab toxin from Bacillus thuringiensis Berliner (i.e., Bt corn), in order to evaluate the potential impact on beneficial insects. Crop resistance of Bt corn hybrid Compa and its non-Bt isoline Dracma to corn borers, Ostrinia nubilalis (Hübner) and Sesamia nonagrioides (Lefebvre), was observed. The attacks by the two pests were always lower in Bt corn than in non-Bt corn plots: at the end of October 5.9 and 19.3 larvae of corn borers per plant were counted in Bt and non-Bt corn respectively. The infestation of aphids, mainly Rhopalosiphum padi (L.), was of the same level in both Bt and non-Bt plots. No significant differences were found between Bt and non-Bt corn for predator counts (mirids, anthocorids, syrphids, chrysopids, coccinellids and arachnids) on sample plants. However, the total number of coccinellids, mainly Propylea quatuordecimpunctata (L.), captured by yellow traps was significantly lower in Bt plots (P=0.05).