A study of feeding by polyphagous predators on cereal aphids using ELISA and gut dissection.
Enzyme-linked immunosorbent assay (ELISA) was used to detect aphid consumption by predators collected from 3 fields of winter wheat in the UK. A total of 7781 predators belonging to 105 species was tested and 81 species were found to have consumed aphids at some time during the study. An unexpectedly high percentage of many species had consumed aphids when aphid density was low, early in the season. The relative efficiencies of ELISA and gut dissection for detecting prey remain varied according to the species of predator tested, and secondary predation was a potential problem, especially in the former technique. In general, staphylinid beetles and beetle larvae digested their aphid meal much more rapidly than carabid beetles and spiders. Field data on percentage of predators positive in ELISA and on predator density were combined with laboratory data on digestion rates to give predation indices which enabled comparison of species in terms of some aspects of their probable value as aphid predators. Spiders usually had the highest predation indices, but mites and adults and larvae of beetles were also of significance as aphid predators. It is concluded that aphid control by polyphagous predators is likely to be widely based.