THE DETECTION OF PREDATION BY ABAX-PARALLELEPIPEDUS AND PTEROSTICHUS-MADIDUS (COLEOPTERA, CARABIDAE) ON MOLLUSCA USING A QUANTITATIVE ELISA

The potential of carabid beetles as natural control agents of slugs wa s investigated using a quantitative indirect enzyme-linked immunosorbe nt assay (ELISA). The crop contents of two species, Abax parallelepipe dus (Piller & Mitterpacher) and Pterostichus madidus (Fabricius) colle cted between May and December 1990, were analysed using an anti-mollus c haemolymph antiserum. The mass, immunological reaction and calculate d mollusc content of each beetle crop was determined. Mollusc content was calculated as 'fresh mollusc equivalent', and the probable quantit ies of degraded material present are discussed in relation to predator and prey species. 89.5% of A. parallelepipedus and 42% of P. madidus were found to contain mollusc proteins. Although approximately the sam e proportion of male and female A. parallelepipedus tested positive, f emales contained greater quantities of mollusc remains. Approximately 39% of male and 45% of female P. madidus tested positive, and overall female crops contained significantly more material. The calculated amo unt of mollusc remains found in females was also greater. Over time, t he immunological reactivity of A. parallelepipedus crop samples varied significantly. However, when crop weight was taken into consideration , the calculated quantity of mollusc found in strongly reacting sample s was not significantly different between months in either species. Ne ither the immunological response nor the quantity of mollusc remains v aried over time in P. madidus, although significant differences were f ound in overall crop weights. A significant correlation was found betw een the proportion of mollusc in beetle crops and crop mass in A. para llelepipedus, but not in P. madidus. Correlations between soil tempera tures and crop mass, immunological reactivity and mollusc content were not significant in either species. The improved methods of quantifyin g predation from ELISA data, employed in this study, were an important part of a larger on-going investigation of the role of predation in s lug population dynamics within agricultural systems.