Spring dispersal and summer habitat distribution of Agonum dorsale (Coleoptera, Carabidae)

A capture-recapture study of the carabid Agonum dorsale in Danish farmland showed that the beetles dispersed several hundred meters in a few weeks from the overwintering site (a field boundary), into adjacent arable fields. Initially, the beetles were mainly found in a winter crop but later they were distributed among winter and spring sown crops. During summer pitfall trapping in seven spring sown crops revealed that the beetles, especially the females, were found in highest numbers in broad bean fields and lowest numbers in sugar beet, spring wheat and spring rape fields. The male/female sex ratio decreased from 0.43 in spring to 0.23 in mid summer. Dissection of specimens trapped in the pitfalls revealed that 71% of the males and 80% of the females had full or half full crops. In late summer larvae were found in highest numbers in the oat, lucerne, bean and rape fields and very few individuals were captured in the beet field. The habitat distribution is discussed in relation to microclimatic conditions, prey availability and agricultural practices.