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Carabid beetles (Coleoptera: Carabidae) were fed upon slugs (Mollusca: Pulmonata) in the laboratory, and their crop contents analysed for mollusc remains, using an enzyme-linked immunosorbent assay (ELISA) with an anti-Arion ater (L.) haemolymph antiserum. Crop weight loss and antigenic recognition of prey proteins were examined as separate variables in a series of validatory experiments. Two model predators, Abax parallelepipedus Piller and Mitterpacher and Pterostichus madidus F., were fed upon two species of pest slugs, Deroceras reticulatum (Muller) and Arion hortensis Ferussac. The fitting of regression equations to the transformed antigenic response data allowed the ‘half-life’ and detection period to be calculated for each predator-prey combination. Following a one hour feeding interval, the half-life of the antigenic response to D. reticulatum remains was almost twice as long in P. madidus as that in A. parallelepipedus, and the detection period more than 2.5 times as long. However, covariant analysis showed that there was a significant difference between predator species in the rate at which detectability declined, but not in the rate of crop weight loss. When A. parallelepipedus was allowed to feed upon A. hortensis for eight hours, prey remains were still detectable at the end of the experiment, 13 days after feeding. Calibration of the differential rates of antigen decay and crop weight loss could potentially be used to calculate the size of the original meal, but only if prey species, and the time since feeding, can be determined. Potential solutions to these problems are discussed. |
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