Insect pests and spiders in oilseed rape and their response to site and landscape factors

Abstract

The abundance of the insect pests: pollen beetle (Meligethes aeneus), stem weevils (Ceutorhynchus napi, C. pallidactylus) and brassica pod midge (Dasineura brassicae), pest damage, species richness and activity density of spiders, and density, body size and offspring of the wolf spider, Pardosa agrestis, in oilseed rape fields relative to site and landscape factors were investigated. Abundances of pollen beetles and stem weevils were significantly positively correlated with soil quality and negatively related to oilseed rape area in the surroundings. Generally, abundances of all groups were positively related to woody areas. Damage by pollen beetle and pod midge was negatively correlated with rape area, damage by the stem weevils responded positively to soil index. Spider richness was positively related to woody areas at small spatial scale, spider density increased with length of road-side strips at large scale. Also, body size of P. agrestis was best explained by length of road-side strips and number of offspring increased as distance to woody areas decreased. Non-crop areas surrounding rape fields promoted both spider fitness and assemblages in rape fields, thus underlining the importance of these habitats for biological pest control. This may become particularly significant as future plans to boost biofuel production will drastically reduce non-crop areas in agricultural landscapes. Our finding that the spatial configuration of non-crop habitats favours predators indicates that landscape management strategies should focus on interspersing non-crop habitats within the matrix of arable fields in a way that distances between refuge or source habitats and arable fields are kept short. © 2010 Springer Science+Business Media B.V.