Ground beetle (Coleoptera: Carabidae) activity density and community composition in vegetationally diverse corn agroecosystems

Influences of weeds on activity density (number captured per trap per day), species richness and diversity of carabids (Coleoptera: Carabidae) in reduced tillage corn (Zea mays L.) plantings were examined in a 2-yr field study. Four treatments were examined: corn monoculture, corn with broadleaved weeds, corn with grassy weeds, and corn with a mixture of broadleaved and grassy weeds. Carabids were sampled with pitfall traps every 3-4 wk from May to September in 1988 and 1989. Neither broadleafed nor grassy weeds significantly influenced carabid activity density in 1988, a year of severe drought. However, in 1989, a year of normal rainfall, activity density was significantly greater in broadleaved weed treatments. Activity density of each of the major carabid species was affected differently by the treatments. Weedy vegetation in corn plantings generally did not have significant effects on carabid species richness, and community similarity was generally high for all treatments. Weeds had a significant negative effect on corn yields; the possible beneficial effects of such vegetation on enhancement of carabid activity density should be compared to the potential negative effect of corn yield loss. These results suggest carabid species respond differently to vegetational diversity, perhaps due to a number of factors, including suitable prey availability and microclimate preferences.