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 ann ual crops but may be limited in impact by the frequent and intense disturba nces 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 soy bean, Glycine max L. Merr, oats, Avena sativa L., and corn, Zea malls L., r otation. Refuges consisted of a central strip of 3 perennial flowering plan ts, Agastache foeniculun (Pursh) O. Kuntze, Origanum vulgare L., and Scropu laria nodosa L, with orchard grass, Dactylis glomerata L., white clover, Tr ifolium repens L., and sweet clover, Melilotus officinalis L., seeded on ea ch side. A cover crop was present only in 1996 and consisted of frost seede d red clover; Trifolium pratense L. A total of 5,117 and 2,316 carabid beet les was captured in pitfall traps comprising 14 species in 1996 and 20 spec ies 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 su bplots without a cover crop. There was no carryover effect of cover crop on beetle activity-density in 1997. Among the most abundant species, a greate r proportion of captures of the fall breeding species Pterostichus melanari us (Illiger), Pterostichus permundus (Say), and the spring breeding species Poecilus lucublandus (Say) occurred in the refuge strips. The spring breed ers Poecilus chalcites (Say), Harpalus herbivagus Say, and Agonum cupripenn e (Say), and the phytophagous fall breeder Harpalus pensylvanicus (De Geer) occurred in greater proportions in the crop areas. The potential use of th ese strategies for conserving carabid beetles in agricultural systems is di scussed.