Abstract

Cropland under conservation-tillage (consT) is increasing in the Palouse region of Idaho, with implications for the conservation of epigeal beetles across the 'matrix' (managed habitats surrounding native Palouse prairie). Carabid beetles (Coleoptera: Carabidae) are important for biodiversity and ecosystem functioning (BEF), and are especially valued for their role as biocontrol agents of pests in cropland. Weevils (Curculionidae), darkling beetles (Tenebrionidae) and scarabs (Scarabaeidae) also contribute significantly to BEF, but little is known about these taxa and how they respond to different crop-cultural systems in the matrix.

The effects of crops under conventional-tillage (CT) and consT on the epigeal beetle fauna were studied on-station (in spring pea, barley, wheat and winter wheat plots) and on-farm (in spring pea and wheat commercial fields) over a 3- and 2-yr period, respectively. ConsT included both no-tillage ('NT') and direct-seed ('DS') practices. Mark-recapture experiments were conducted to detect whether pitfall trap capture rates differed for select species ( Poecilus scitulus L., P. lucublandus Say and Pterostichus melanarius Il.) and pitfall data were adjusted to account for sampling biases. The conservation potential of consT for prairie-inhabiting weevils, darkling beetles and scarabs was assessed by sampling five prairie remnants and comparing these fauna with those found in commercial fields under consT and CT.

Diversity and richness of Carabidae were generally higher in consT crops on-station while on-farm this pattern was only observed during the first year of the study. The activity-density (trap catch) of carabids was higher in CT than in consT crops on-station and on-farm, due primarily to elevated activity-density of several spring breeders but especially the native Poecilus scitulus L. Capture rates of pitfall traps were generally higher in CT than in NT wheat, but the opposite pattern was detected in pea.

Biological diversity and richness of weevils, darkling beetles and scarabs was significantly higher in prairie than in agricultural fields. These statistics were higher in CT than in consT when exotic species were included, but lower when only natives were considered. Similarly, when only native species were considered faunal similarity was greater between consT and prairie than between CT and prairie.