The spatial dynamics of crop and ground active predatory arthropods and their aphid prey in winter wheat

Abstract

The distribution of aphid predators within arable fields has been previously examined using pitfall traps. With this technique predominantly larger invertebrate species are captured, especially Carabidae, but the technique provides no estimate of density unless mark-recapture is used. However, many other numerically important aphid predators occur in arable fields and relatively little is known about their distribution patterns nor whether they exhibit a density-dependent response to patches of cereal aphids. Identification of the most effective predators can allow management practices to be developed accordingly. In this study, the distribution of cereal aphids and their predators was examined by suction sampling within a field of winter wheat in Devon, UK, along with visual estimates of weed patchiness. Sampling was conducted on four occasions in 1999 across a grid of 128 sample locations. The distribution of 11 predatory taxa from the Carabidae, Staphylinidae and Linyphiidae was examined. Additionally, the total number of aphid predators and a predation index were used in these analyses. Carabid adults and larvae, along with staphylinid larvae showed the strongest aggregation into patches and the most temporal stability in their distribution. Other taxa had more ephemeral distributions as did the cereal aphids. The distribution of carabid larvae was disassociated from the distribution of cereal aphids for the first two sampling occasions indicating biocontrol was occurring. Other predatory groups showed both association and disassociation. Carabid larvae, Bathyphantes and total numbers of Linyphiidae showed a strong correlation with weed cover for two of the sample dates. Cereal aphids were disassociated from weed cover on three sampling occasions.

Agricultural landscape simplification reduces natural pest control: A quantitative synthesis

“…Stability of ecosystem functions is thought to increase with species richness due to niche complementarity, facilitation, or sampling effects (Hooper et al, 2005); a positive relationship that has been found for a variety of ecosystem functions including biomass production, crop pollination, and pest control (Garibaldi et al, 2011;Isbell et al, 2009;MacFadyen et al, 2011). Studies linking natural enemy diversity to pest control services have focused on temporal stability, while spatial stability remains largely unexplored although considerable spatial heterogeneity in terms of abundance of natural enemies and their prey have been observed within fields (Holland et al, 2004;Winder et al, 2005;MacFadyen et al, 2011). Because landscape complexity is known to enhance natural enemy diversity and abundance, we expected to find a lower within-field stability (higher variability) in pest control in simple compared with more complex landscapes.…”

Effect of Bt-maize on epigeic spiders (Araneae) and harvestmen (Opiliones)

“…As this was similar for all plots, this displacement may result from different habitat preferences. Web-builders build their webs in ground crevices and prefer denser vegetation cover, presumably due to higher moisture (HOLLAND et al 2004). On the other hand, hunting spiders prefer open habitats of bare ground to sparse vegetation (BOGYA & MOLS 1996).…”

Contrasting the farm-scale spatio-temporal dynamics of boundary and field overwintering predatory beetles in arable crops

“…More specifically, an understanding of how species respond that utilise different habitat areas within the farmed landscape. The provision of extra field margin habitats may increase numbers within fields but these features can, however, also act as barriers to dispersal preventing movement between fields (Thomas et al 1998;Fernandez-Garcia et al 2000;Holland et al 2004b). Movement is essential if beneficial arthropods are to respond to pest infestations that are spatially dynamic and if recovery is to occur following population reductions such as those caused by intensive tillage or insecticides.…”