Activity and satiation state in Pterostichus melanarius: an experiment in different agricultural habitats

1. A capture-recapture experiment was conducted to examine the effects of s atiation state on the activity and foraging efficiency of the carabid beetl e Pterostichus melanarius Ill., in four different habitats (a hedge, a tran sition zone between the hedge and the adjacent wheat crop, the margin of th e wheat crop, and the centre of the wheat crop) in an agricultural ecosyste m in France. 2. Prey biomass and density decreased from the centre of the hedge to the c rop margin and to the centre of the crop, where prey density was low but pr ey biomass was moderate. Starved and satiated beetles were released in circ ular enclosures and recaptured using pitfall traps for 6 days. 3. Immediately after release, starved P. melanarius were significantly more active than satiated beetles, but this difference disappeared after the fi rst day. At each recapture date, starved individuals had gained weight wher eas satiated individuals had lost weight. The analysis of activity and weig ht variation at the end of the first day indicated that the centre of the c rop seemed to be the most favourable habitat for starved individuals to fin d food rapidly, whereas the behaviour of satiated individuals was identical in all habitats. 4. This experiment shows that habitat use of P. melanarius is flexible. The results are discussed in the context of the classical view of foraging beh aviour in carabid beetles. The activity and foraging efficiency in P. melan arius in different habitats can be explained as the result of the interacti on between individual satiation state, prey availability in the habitat, an d particular preferences of the species.