Shelterbelts in agricultural landscapes enhance ladybeetle abundance in spillover from cropland to adjacent habitats

Abstract

The natural enemies of herbivorous pests in cropping systems may relocate to adjacent habitats in response to declining habitat quality in heterogeneous landscapes. In this study, we measured the cross-edge spillover of ladybeetles from wheat fields to shelterbelts, and tested how landscape variables at various spatial scales influence ladybeetle populations. We conducted a large-scale sampling study of agricultural landscapes differing in structural complexity during 2012 and 2013. The effects of landscape variables (i.e., landscape diversity and the percentage of woody habitats) on the ladybeetle abundance were investigated. Propylea japonica (Thunberg) and Harmonia axyridis (Pallas) were the dominant ladybeetle species. The abundances of ladybeetles in spillover were positively correlated with the percentage of woody area, and negatively correlated with landscape diversity and edge density of crop habitats. It indicates that a low diversity landscape with a large area of shelterbelts supports larger ladybeetle abundance in spillover compared with a high diversity landscape with a limited area of shelterbelts. By contrast, greater numbers of within-field ladybeetles were associated with landscape diversity increase. Landscape features at the spatial scale of 2.5–3 km could best predict the abundance of ladybeetles in spillover, whereas the best prediction model for ladybeetle abundance within field was at the 1.5 km scale. These results suggest that the landscape variables influence ladybeetle abundance differently in spillover and within fields. The introduction of shelterbelts in the agricultural landscape could enhance the conservation of ladybeetle populations.