Carabid activity-density and community composition, and their impact on seed predation in pulse crops

Reduced use of chemicals in weed management has been identified as a key strategy to increase overall agricultural sustainability. Carabid (Coleoptera: Carabidae) and cricket (Orthoptera:Gryllidae) weed seed predation has shown promise, but also variability, as an additional weed management tool. Therefore, it is important that carabid activity-density and weed seed predation is further explored in a wide variety of crops and cropping systems, including large conventional systems where sustainability gains may be the largest. Here we explored carabid and cricket activity-density, community, and weed seed consumption in commercial conventional pulse crop fields. Pulse crops are increasingly being incorporated in cropping rotations but weed seed predation is hardly explored in this group of crops. We sampled twenty-four large commercial lentil, pea, faba bean, and soybean fields, and found that crop type did not affect levels of seed predation or carabid activity-density but was a factor in shaping the carabid + cricket community. Crop history had an unexpectedly large impact on the community, fields previously planted to canola had relatively high Amara activity-densities. The carabid genera Amara and Pterostichus, as well as crickets were associated with volunteer canola seed predation. None of the studied carabid taxa, nor crickets, were a significant factor explaining kochia seed predation. We also explored the effects of crop canopy-driven microclimate factors on carabid and cricket activity-density and weed seed predation. The Amara, the most abundant granivorous taxon in this study, were positively related to soil temperatures but not to soil light intensity. Our study highlights the importance of cropping history on the community of beneficial insects in crop fields and indicates a taxon specific relationship with soil temperature and weed seed predation.