Carabid beetle communities after 18 years of conservation tillage and crop rotation in a cool humid climate

Agricultural practices affect the biotic and abiotic conditions that determine food and shelter for carabid beetles (Coleoptera: Carabidae). We hypothesised that carabid communities would respond differently to 18 years of contrasted cropping practices in cereal-based rotations. We measured the effects of tillage (MP: moldboard plough; CP: chisel plough; NT: no-till) and previous crop sequence (cereal monoculture versus cereal-forage/cereal-oilseed rotation) on carabid beetle activity density, diversity, and community structure in corn (Zea mays Linnaeus, Poaceae) at La Pocatière, Québec, Canada. Carabid beetles were sampled monthly from May to September 2006, using pitfall traps. Although 19 carabid species were observed, assemblages were dominated by Harpalus rufipes (De Geer), particularly in the second half of the season. Multivariate analyses indicated a strong affinity of carabid species for the NT treatment throughout the season. Crop sequence and tillage had no effect on diversity (Shannon's H'≤ 1.3) and evenness of carabid assemblage, but species richness and activity density were greater in NT than in tilled systems. Peak activity density of dominant species occurred at different times during the season, generally in accordance with preferred breeding season. Many species had greater activity density in NT than in tilled treatments. Because of their granivorous feeding habit, carabid populations such as that of H. rufipes could be an important asset to NT, given the limited weed management options available for this system. © Copyright 2012 Entomological Society of Canada.