The detection of predation byAbax parallelepipedusandPterostichus madidus(Coleoptera: Carabidae) on Mollusca using a quantitative Elisa

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Abstract
The potential of carabid beetles as natural control agents of slugs was investigated using a quantitative indirect enzyme-linked immunosorbent assay (ELISA). The crop contents of two species,Abax parallelepipedus(Piller & Mitterpacher) andPterostichus madidus(Fabricius) collected between May and December 1990, were analysed using an anti-mollusc haemolymph antiserum. The mass, immunological reaction and calculated mollusc content of each beetle crop was determined. Mollusc content was calculated as ‘fresh mollusc equivalent’, and the probable quantities of degraded material present are discussed in relation to predator and prey species. 89.5% ofA. parallelepipedusand 42% ofP. madiduswere found to contain mollusc proteins. Although approximately the same proportion of male and femaleA. parallelepipedustested positive, females contained greater quantities of mollusc remains. Approximately 39% of male and 45% of femaleP. madidustested positive, and overall female crops contained significantly more material. The calculated amount of mollusc remains found in females was also greater. Over time, the immunological reactivity ofA. parallelepipeduscrop samples varied significantly. However, when crop weight was taken into consideration, the calculated quantity of mollusc found in strongly reacting samples was not significantly different between months in either species. Neither the immunological response nor the quantity of mollusc remains varied over time inP. madidus, although significant differences were found in overall crop weights. A significant correlation was found between the proportion of mollusc in beetle crops and crop mass inA. parallelepipedus, but not inP. madidus. Correlations between soil temperatures and crop mass, immunological reactivity and mollusc content were not significant in either species. The improved methods of quantifying predation from ELISA data, employed in this study, were an important part of a larger on-going investigation of the role of predation in slug population dynamics within agricultural systems.