Influence of refuge habitats and cover crops on seasonal activity-density of ground beetles (Coleoptera: Carabidae) in field crops

Carabid beetles are important predators of arthropods and weed seeds in annual crops but may be limited in impact by the frequent and intense disturbances imposed on these systems. Pitfall trap sampling conducted in 1996 and 1997 examined the effect of refuge strips and cover crops on enhancing the seasonal activity-density of carabid beetles. The study site followed a soybean, Glycine max L. Merr, oats, Avena sativa L., and corn, Zea malls L., rotation. Refuges consisted of a central strip of 3 perennial flowering plants, Agastache foeniculun (Pursh) O. Kuntze, Origanum vulgare L., and Scropularia nodosa L, with orchard grass, Dactylis glomerata L., white clover, Trifolium repens L., and sweet clover, Melilotus officinalis L., seeded on each side. A cover crop was present only in 1996 and consisted of frost seeded red clover; Trifolium pratense L. A total of 5,117 and 2,316 carabid beetles was captured in pitfall traps comprising 14 species in 1996 and 20 species in 1997. Carabid beetle seasonal activity-density was greater (1996) or equal (1997) in refuge strips than in control areas without refuge strips; however, the presence of a refuge strip did not alter carabid populations in the surrounding subplots in either year. In 1996, subplots containing a cover crop had significantly higher carabid beetle activity-density than subplots without a cover crop. There was no carryover effect of cover crop on beetle activity-density in 1997. Among the most abundant species, a greater proportion of captures of the fall breeding species Pterostichus melanarius (Illiger), Pterostichus permundus (Say), and the spring breeding species Poecilus lucublandus (Say) occurred in the refuge strips. The spring breeders Poecilus chalcites (Say), Harpalus herbivagus Say, and Agonum cupripenne (Say), and the phytophagous fall breeder Harpalus pensylvanicus (De Geer) occurred in greater proportions in the crop areas. The potential use of these strategies for conserving carabid beetles in agricultural systems is discussed.