The efficacy of baited and live capture pitfall traps in collecting large-bodied forest carabids.

Abstract

Pitfall trapping is commonly used to sample epigaeic invertebrates throughout the world. However, this technique can be ineffective for capturing some species, whilst capturing high numbers of nontarget invertebrates. This study aims to improve the efficacy of pitfall trapping for sampling Mecodema spp. (Coleoptera: Carabidae), but also examines the potential of live pitfall traps to reduce the by-catch of other invertebrates. Four types of pitfall traps were used in two separate sampling regimes: baited kill trap versus nonbaited kill trap, and chambered live trap versus non-chambered live trap, in regenerating kauri/ broadleaf mixed forest (Waitakere Ranges, Auckland, New Zealand). Results show all four types of traps sampled different components of the invertebrate community. Baited kill traps caught extremely high numbers of some groups, particularly Diptera and Coleoptera, whereas non-baited kill traps caught far fewer individuals of these groups. Both types of live capture traps caught few individuals. Three genera of large-bodied Carabidae (Ctenognathus, Holcaspis and Mecodema) were caught in similarly low numbers in both baited and non-baited traps indicating that baiting with squid is ineffective as an attractant to increase catch rates of the genus Mecodema. Although baiting did not increase carabid catches it appears that live traps worked as well as kill traps, but live traps caught fewer invertebrates and therefore significantly reduce the bycatch. A negative aspect of live pitfall trapping is the potential of captured invertebrates to prey upon each other. However, no predation was observed within the traps during this study.