Effect of woody borders on insect density and diversity in crop fields: a landscape-scale analysis

The relationship between density and richness of herbivorous insects in alfalfa fields, and the amount (total length) of woody field border in the landscapes surrounding the fields was studied. Insects (predominantly herbivorous) were sampled in 35 alfalfa fields in 1995 and 24 fields in 1996, and the total length of woody field borders within the 1 km radius circular landscape surrounding each field was measured. There was no effect of amount of woody border in the landscape on insect density. There was a significant positive effect of amount of woody border in the landscape on overall family richness of insects in the alfalfa fields. The results of this study suggest that woody borders increase diversity but not density of herbivorous insects within crop fields in agro-ecosystems. This suggests that woody borders play a role in maintaining biodiversity in agro-ecosystems, and that this role extends beyond the borders themselves, into the crop fields. (C)2000 Elsevier Science B.V. All rights reserved.