Linking landscape structure, floral resource distribution, pollen use and movement distances of a generalist predator

Abstract

Understanding the habitat use and movement patterns of natural enemies in agricultural landscapes is essential for enhancing biological pest control. Since many natural enemies rely on floral resources, the distribution of these resources in combination with movement behaviour likely influence biological control in field crops. Nevertheless, few studies have assessed natural enemy movement at the landscape scale.Here we estimated minimal movement distances of the green lacewing Chrysoperla carnea based on consumed pollen and the spatial distribution of the respective plant species in 24 agricultural landscapes (500 m radius). Lacewings were sampled using sticky traps in the centre of each landscape, and the consumed pollen were identified. The location of the most important pollen-providing plants was mapped in each landscape. Distances to potential sources of pollen consumed by 346 lacewings were used to derive minimal movement distances.Lacewings consumed mostly pollen from insect-pollinated plants that were present within 500 m from the sampling location. The distance to the nearest source of consumed pollen exceeded 200 m in 31% of lacewing individuals, demonstrating the relevance of the landscape scale to understand their population dynamics.Distances were shorter to insect-pollinated than to wind-pollinated plants, and shorter early than late in the season. Mean and median distances to pollen sources were negatively associated to flower availability and edge density in the landscape, but this was not the case for minimal distances.Synthesis and applications. Our findings suggest that the spatial distribution of flowering wild plants can inform movement patterns of lacewings and other flower-visiting insects in agricultural landscapes. In addition, the location of floral resources in the landscape is important for its capacity to sustain natural enemies. Given the strong reliance of lacewings on pollen from nearby insect pollinated woody plants, the promotion of native shrubs and trees, such as Prunus, Salix and Castanea, should be prioritized for natural enemy enhancement in agricultural landscapes. Doing this in the form of hedgerows or agroforestry systems would lead to only minimal reduction in production areas and provide additional benefits such as biodiversity conservation.