Response of carabid assemblages to genetically modified herbicide-tolerant corn and to some sustainable farming practices

In agricultural lands, predation of arthropod pests by natural enemies provides a tool for the development of farming strategies that rely less on insecticides. The Carabidae is a speciose family of beetles that constitute a large portion of these natural enemies and are known to be affected by farming practices. To investigate the impact of new farming practices on carabid assemblages, I used pitfall traps throughout the growing season in (1) experimental plots of conventional and genetically modified herbicide-tolerant (GMHT) corn under continuous and rotation regimes and (2) experimental plots of a rotation of wheat, potato and bean under sustainable and conventional farming practices. GMHT corn had a significant influence on the carabid assemblages in one of the two years investigated. It was associated with reduced activity density of the dominant species, Bembidion quadrimaculatum. Higher mid-season weed density in plots with GMHT corn is likely to explain these results. Rotation of corn with canola increased the activity density, lowered the diversity and modified the carabid community structure. Sustainable farming increased the activity density of carabids but did not increase diversity or significantly change the community structure. However, click beetle populations, which are potential pests, were also enhanced under sustainable farming. Many carabid species were associated with different crops which affected the year to year variation on community structure.