Shelterbelts in agricultural landscapes enhance ladybeetle abundance in spillover from cropland to adjacent habitats
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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.
KeywordsCoccinellid Dispersal Natural enemies Winter wheat Woody border Agroforestry
We are grateful to Dr. Felix Bianchi for guidance on the analysis and to Dr. Marvin Harris for reviewing the manuscript draft. We appreciate Xiuxiu Wang’s assistance at the image interpreting and field investigation. Many farmers in the Yucheng area made this study possible by allowing access to their fields. This work was supported by the National Basic Research Program of China (973 Program) (2013CB127604), National Nature Science Fund of China (Nos. 31030012 and 31200321) and the State Key Laboratory of Integrated Management of Pest Insects and Rodents (Grant No. Chinese IPM1412).
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