Seasonal shifts in ground beetle (Coleoptera: Carabidae) species and functional composition maintain prey consumption in Western Oregon agricultural landscapes

Abstract

Ground beetles (Carabidae: Coleoptera) are generalist predators that contribute to biological control of agricultural pests. Different ground beetle species vary in terms of size, feeding habits, and season of adult and larval activity. Species with similar biology and feeding habits may form a functional group if they are also similar in their effect on the overall risk to a potential prey item in an area. Farm surveys and laboratory studies were conducted to test whether ground beetle populations on Western Oregon vegetable farms were associated with the predation risk of a sentinel prey item. Pitfall traps were used to measure the activity patterns of adult beetles throughout the year. Along with the monthly pitfall traps, sentinel prey cards were deployed to measure the risk of predation to a potential prey item by a carabid beetle on the landscape. Additionally, beetles were collected after pitfall trapping to measure the amount of the sentinel prey items they would eat. The ground beetle species collected in the sampling were placed into three size based groups. The phenology and feeding habitats of the species within each sized based group tended to be similar. Sentinel prey removal rates in the field were significantly increased in areas with high activity of midsized beetles during the spring, when midsized beetles were the most active on the landscape but the explanatory power was somewhat low. In the summer, when large beetles were active in the landscape, sentinel prey removal rates were similarly associated with large beetle activity densities.