Abundance and diversity of ground-dwelling arthropods of pest management importance in commercial Bt and non-Bt cotton fields

The modified population dynamics of pests targeted by the Cry1Ac toxin in Bacillus thuringiensis (Bt) transgenic cotton (Bt cotton) and possible reduced insecticide use in these transgenic varieties may exert a variety of effects on ground-dwelling predator communities. A survey of ground-dwelling arthropods was carried out weekly each of 3 years (during the cropping season) in commercial Bt and non-Bt cotton fields. Sixty-five taxa of ground-dwelling arthropods (carabids, cicindelines, staphylinids, dermapterans, heteropterans and araneids) of importance for cotton pest management were recorded in the survey. Species abundance and dynamics across seasons were evaluated with univariate analysis of variance for higher taxa or multivariate principal response curve analysis for the whole community of 65 taxa. Diversity and richness indices and cumulative species curves also were calculated. The analyses demonstrated no differences in the ground-dwelling arthropod communities between cotton types. One araneid species, Pardosa pauxilla, comprised ~80% of all araneids, Labidura riparia comprised ~96% of all dermapterans, Megacephala carolina comprised ~97% of cicindelines and four carabid species (Selenophorus palliatus, Apristus latens, Harpalus gravis and Anisodactylus merula) comprised ~80% of carabid species. M. carolina outnumbered all other collected species in each of the 3 years. When only predatory carabid species were considered, A. merula, Calosoma sayi, Harpalus pennsylvanicus and Stenolophus ochropezus were predominant and numbers trapped were similar between cotton types. The abundance of dermapterans, staphylinids, araneids and heteropterans varied among sample dates and across seasons but did not differ between cotton types. The frequent capture of M. carolina, S. palliatus and P. pauxilla in all fields and seasons in both cottons suggests that these species may be important for monitoring further changes in local communities as result of agricultural practices.