The efficiency of pitfall traps in relation to a density and activity of the carabid beetle, Carabus insulicola insulicola Chaudoir (Coleoptera: Carabidae), under controlled population density

Abstract

The efficiency of pitfall traps was investigated using two size of enclosure (5 m X 5 m and 10 m X 10 m) in grassland under controlled population density of marked carabid beetles (Carabus insulicola insulicola Chaudoir, 1869) and different number of traps. Pitfall traps were evenly located in every enclosure. Checks on the pitfall traps were carried out every one or two hours on several days in July and August 2002. The efficiency of pitfall traps was correlated with the density of beetles, but not to the size of enclosure. In 5 m X 5 m enclosure, the efficiency of individual pitfall traps was higher at about 2 m intervals of traps compared to 1 m, but the total number of caught beetles was higher at 1 m intervals than about 2 m. In this season this carabid beetle is nocturnal, but the activity of beetles was not steady. It increased rapidly from sunset to midnight and decreased by slow degrees from midnight to sunrise. It is thought that not all individual beetles were active each night, and that the activity patterns resulted from beetles reducing their activity according as individuals fed. From these results, a few points concerning the field research of this carabid beetle were suggested.