Six-year monitoring of non-target arthropods in Bt maize (Cry 1Ab) in the European corn borer (Ostrinia nubilalis) infestation area Oderbruch (Germany)

Abstract

This study was performed in the Oderbruch region, a landscape where Ostrinia nubilalis occurs in high densities. From 2000 to 2005, field pairs (half-fields) planted with Bt maize (Cry 1Ab) and a conventional maize variety, respectively, were investigated using different monitoring methods (visual counts, whole-plant harvesting and pitfall trapping) to determine densities of taxa on plants, activity densities and diversity of ground-dwelling arthropods. A total of 48 taxa were determined in counts and 90 in whole-plant harvests; 75 carabid species and 62 spider species were identified by pitfall trapping. Density comparisons of different taxa, such as aphids, thrips, heteropterans, aphid specific predators, spiders and carabids, revealed a few significant differences for specific taxa but no general tendencies during the six years. Canonical corresponding analyses revealed small but statistically significant differences in community composition between Bt and conventional maize fields. Generally, year-to-year changes in environmental conditions, field characteristics, and population dynamics had much stronger effects on the arthropod community than the use of Bt maize. Three baselines were used for evaluation of findings: (1) mean and variation of a specific variable (e.g. density) in a given conventional maize field, (2) mean and variation of a specific variable in conventional maize fields in the last five years and (3) mean and variation of a specific variable in conventional maize fields within a given year. This methodological approach is tested for suitability for case-specific monitoring.