Landscape-scale cover of different crop hosts, rather than semi-natural grassland habitats, drive crop infestation and parasitism of a generalist insect pest in wheat

Authors: Rand, Tatyana; Peirce, Erika

Submitted to: Agriculture, Ecosystems & Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/14/2025
Publication Date: N/A
Citation: N/A

Interpretive Summary: Cross-site and cross-year changes in the composition of cropped areas can exert strong, yet infrequntly measured, influences on crop pests and their biological control agents. We carried out a large-scale sampling study to investigate the influence of different crop and semi-natural grassland resource habitats on Cephus cinctus, a major pest of wheat, and its parasitoids from field to landscape scales. Both insects were common in rangeland and Conservation Reserve Program grasslands, but densities were significantly (4-7X) higher in wheat, and pest densities were significantly (3X) higher in winter wheat relative to spring wheat. Neither proximity to, nor landscape cover of, grasslands were important predictors of pest infestation or parasitism in wheat. Instead, winter wheat cover in the previous year was the strongest predictor of infestation, while spring wheat cover in the previous was the strongest predictor of parasitism. The study demonstrated that the cover of specific host crops can be important landscape drivers of pest pressure, that pests and natural enemies can respond to different host crop types, and that crop cover from the previous growing season can be more predictive of pressure and parasitism than the within-year cover. Carefully dissecting the influences of different crops, in addition to grassland habitats, and considering the temporal dimension of shifting host crop resources will be critical to improving the prediction of insect responses to landscape complexity and developing pest suppressive landscapes.

Technical Abstract: Studies examining the importance of landscape complexity for conservation biological control have traditionally focused on the benefits of semi-natural habitats. A growing body of recent work demonstrates that spatiotemporal variation in the composition of cropped areas can additionally exert strong influences. We carried out a large-scale sampling study to investigate the influence of different crop and semi-natural resource habitats on Cephus cinctus, a major pest of wheat, and its parasitoids from local to landscape scales. Both insects were common in semi-natural grasslands (rangeland and set-asides), but densities were significantly (4-7 –fold) higher in wheat, and pest densities were significantly (3-fold) higher in winter wheat relative to spring wheat. Neither proximity to, nor landscape cover of, semi-natural grasslands were important predictors of pest infestation or parasitism in wheat. Instead, winter wheat cover in the previous year was the strongest predictor of infestation, while spring wheat cover in the previous was the strongest predictor of parasitism. The study highlights that the cover of specific host crops can be important landscape drivers even for habitat generalists, that pests and natural enemies can respond differently to host crop types, and that crop cover from the previous year can be more influential in predicting pest pressure and parasitism than the within-year cover. Carefully dissecting the influences of different crops, in addition to semi-natural habitats, and considering the temporal dimension of shifting host crop resources will be critical to improving the prediction of insect responses to landscape complexity and developing pest suppressive landscapes.