Carabidae in conservation biological control: The distributions, activity patterns, and feeding habits of common western Oregon ground beetles, and their relation to pest predation risk across agricultural landscapes

Background/Question/Methods

Conservation biocontrol involves adapting farm practices and managing the landscape to enhance naturally occurring beneficial predators of agricultural pests. The challenge is to determine which local species are agriculturally important predators, and what constitutes necessary habitat. Ground beetles are widespread, consume a variety of pest species, and numerous species can be abundant in western Oregon agricultural fields. Several ecological field studies and laboratory experiments were used to help understand the distributions, activity patterns, and feeding habits of common western Oregon ground beetles, and their relation to pest predation risk. Grids of pitfall traps, extending across several fields and into the adjacent, non-cropped habitats, were installed on four vegetable farms and sampled over four years. Predation risk across the pitfall grid was measures with sentinel prey cards baited with fly pupae. Berlese extraction of soil cores was used to sample inactive beetles in their winter habitats. All the samples were located on detailed maps to document patterns in beetle distribution with respect to the various habitats on the landscape. To determine the biological and behavioral processes that were driving the activity patterns, several species were collected during trapping, subjected to feeding and activity trials, and dissected to determine fertility state.

Results/Conclusions

Common ground beetle species of western Oregon agricultural areas vary in their seasonal activity levels. This variation is driven by different breeding seasons and overwintering stages of common species. Laboratory activity levels, voracity, and the proportion of animal prey consumed tended to be higher during the middle part of their activity season. Reproductive structures tended to begin development earlier in males than females, and the peak reproduction period generally corresponds with maximum activity and feeding rates. Several species that overwinter as adults were found to have maximum activity in agricultural fields in the summer, but in the winters numbers were highest in grassy field margins and lowest in areas dominated by blackberry brambles or annually cultivated crop fields. Activities of other species were concentrated around areas with perennial vegetation, although some became more evenly distributed as the season progressed. High activity densities of ground beetles were associated with larger numbers of sentinel prey consumed on adjacent prey stations. With this sort of information we can begin to identify links between specific pests, which transition into and out of vulnerable life stages over the season, and specific predators, which are actively hunting for vulnerable prey during particular times of the year.