Effect of predator size and temperature on the predation of Deroceras reticulatum (Muller) (Mollusca) by carabid beetles

Twenty-one carabid species were used in a laboratory study to determine the effect of beetle size and temperature on the predation of one day old Dero ceras reticulatum (Muller) slugs. The beetles were caught in arable land at the study site. None of the five small-sized beetle species killed slugs, whereas five of the seven medium-sized beetle species and eight of the nine large-sized beetle species killed slugs. Four of the most abundant beetle species at the study site were used to assess the effect of temperature on the predation of 1-day-old slugs. There were significant differences in the proportion of beetles predating slugs at the different temperatures. Regre ssion analysis showed that there was a significant increase in the proporti on of Pterostichus madidus (Fabricius) and Harpalus rufipes (Degeer) beetle s predating slugs as temperature increased. Nebria brevicollis (Fabricius) inflicted its highest level of slug mortality at 8 degreesC and its larvae were the only predators to significantly increase slug mortality at 4 degre esC, the lowest experimental temperature. Harpalus aeneus (Fabricius) infli cted significant levels of slug mortality at 20 degreesC, the highest exper imental temperature. It appeared that the predatory activity of these beetl e species at the five experimental temperatures reflected their annual acti vity periods in the field.