Capture efficiency of fenced pitfall traps for predatory arthropods within a cereal crop.

Abstract

Invertebrates are frequently used as bio-indicators in agroecosystems and a variety of sampling techniques have been developed to estimate their abundance and activity, but many have considerable limitations reviewed by Sunderland et al. (1995). Many of these limitations are a result of their responsiveness to changes in their environment. Activity and abundance is strongly influenced by climatic conditions, vegetation, soil texture and surface features, which in turn effects the efficiency of the sampling techniques (Sunderland et al., 1995). Estimating invertebrate density alone is particularly important in comparative studies where the treatments may cause indirect or direct effects on activity. For example pesticide treatments which are only toxic to pests may leave predatory species without food causing an increase in their activity and capture rate in activity dependant trap types e.g. pitfall traps.
Fenced pitfall traps, which consist of a pitfall trap surrounded by an enclosure from within which the majority of invertebrates can be captured over several weeks, are suitable for determining the density of some ground active species. The enclosures have been constructed of wood (e.g. Dennison & Hodkinson, 1984) or metal (e.g. Bonkowska & Ryszkowski, 1975). The tops of the enclosures must be sealed sufficiently to prevent ingress or migration.
The efficiency of fenced pitfall traps has been evaluated to some extent using mark-recapture in pasture (Descender, van den Broeck & Maelfait, 1985), woodland (Dennison & Hodkinson, 1984) and in rye and potato crops (Bonkowska & Ryszkowski, 1975). The technique therefore appears to be accurate for some species (Sunderland et al., 1995) with estimates being similar to those from soil sampling (Descender and Maelfait, 1983). In this study mark-recapture was used to investigate the efficiency of fenced pitfall traps for ten beneficial insect species in a spring barley crop. Insect activity as a result of intra-species and inter-species interaction may influence capture rate and efficiency, therefore different densities of insects were used.