Landscape heterogeneity and pesticide reduction favor predation, but also grape infestation by Lobesia botrana

Abstract

Biological pest control is a major ecosystem service and is known to depend on landscape heterogeneity. The composition and configuration of landscapes can affect natural enemy communities, trophic interactions, and pest density within agroecosystems. However, local agricultural management can interfere with natural enemy activity, so the positive effects of landscape heterogeneity may be disrupted by farming practices. Here, we studied the influence of landscape context and management options on the biological control of Lobesia botrana, one of the main insect pests of grapes. We focused on two complementary measures: predation rates, which reflect part of biological control potential, and plant damage, which reflects pest density and the associated infestation. We used a set of sentinel prey (eggs, caterpillars, pupae) to quantify predation rates across different developmental stages of the pest. The study was carried out in a landscape-scale experimental set-up consisting of 38 vineyards in Southwestern France. Using structural equation models, we show that predation rates on sentinel prey were affected by both landscape heterogeneity and local management practices. Higher pest predation rates were observed in landscapes with smaller vineyards and in vineyards with low applications of synthetic pesticides. We observed limited relationships between predation rates and grape infestation levels. However, our results suggest that predation rates at the pest pupae stage are significantly shaping infestation levels. Additionally, pest damage in spring and summer was primarily influenced by the intensity of local pesticide use and the grass cover in the field and exacerbated by the decreasing size of vineyards, while semi-natural habitats had no effect on pest damage. We conclude that links between L. botrana infestation and biological control potential appear tenuous in our study region. This is likely due to the high local management intensity, as evidenced by the negative association observed between pesticide applications and predation rates. Nevertheless, both predation and infestation respond to landscape or field heterogeneity and pesticide use. Reducing the use of pesticides should be combined with multi-scale diversification measures at field and landscape levels to amplify the predation potential.