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(24-04) Bt-maize in Spain: monitoring of corn borers resistance and impact on non-target arthropods. Castaņera, Pedro*,1, Farinos, Gema1, De la Poza, Marta1, Ortego, Felix1, 1 CSIC, CIB. Dpto Biologia de Plantas, Velazquez,144, Madrid, Spain ABSTRACT- A surface ranging from 20,000 to 25,000 ha of Bt-maize (event 176, cv. Compa CB, Syngenta) has been grown annually in Spain since 1998. A project was initiated to detect changes in susceptibility of corn borers through regular monitoring on Bt-maize fields, and to assess the potential impact of Bt-maize on non-target arthropods. Baseline susceptibility to the Cry1Ab toxin was determined for Spanish populations of the Mediterranean corn borer, Sesamia nonagrioides, and the European corn borer, Ostrinia nubilalis from larvae collected on non-transgenic maize in the most important growing areas (Galicia, Ebro, Madrid, Andalucia, Badajoz and Albacete). Annual monitoring of field populations of both species collected on Bt-maize has not revealed changes in susceptibility after three years of Bt-maize cultivation in Spain. Likewise, laboratory selection for eight generations produces minor changes in susceptibility. We have started a study in a commercial field (about 5 ha), near Madrid (Spain), to assess the potential impact of Bt-maize on the abundance and diversity of non-target arthropods. Bt-maize (cv. Compa CB) was compared with the isogenic cv. Dracma under conventional farm practices. Three replicates (0.6 ha/plot) were arranged in a completely randomised block design. Visual counts and pitfall traps were used to compare their effects on non-target arthropods from late June to the end of September. Visual surveys reveal that Orius spp. and spiders were the most abundant predators on the maize plants. A common pattern of the frequency of Orius on plants was found in both years, with few specimens at the beginning of the summer and a big increase in September. Conversely, spiders were present in the plant all through the summer. Ground beetles and spiders were the most abundant poliphagous predators found in pitfall traps in all treatments. Five carabid species accounted for 98% of the total beetles collected. Similarly, six species of spiders accounted for 97% of their total number. No detrimental effects associated with the transgenic cultivars have been detected so far, although no firm conclusions can be drawn until these studies are completed. Key words: transgenic plants, Bt-corn, corn borer, natural enemies |
