An enzyme-linked immunosorbent assay (ELISA) was used to examine the digestive tracts of potential predators collected from an experimental cabbage plot in Victoria, Australia, for antigens of
Pieris rapae(L.). The rabbit serum used in the study was made against an extract of all immature stages of the prey species and was shown to interact with proteins representing all immature stages. The serum was also shown not to react with antigens from other pest species collected from the experimental plot or with predators not exposed to the prey. The main predators found using the assay were the labidurids Nala lividipes(Dufour) and Labidura riparia truncataKirby, the staphylinid Thyreocephalus cyanopterus(Erichson) and the eusparassid Olios diana(L. Koch). These results agree closely with laboratory observations on predation. The assay was sensitive, allowing 2000 assays to be performed per millilitre of serum and thus a single serum collection of 20 ml permitted about 40 000 assays.