Impact of predatory carabids on below- and above-ground pests and yield in strawberry

The impact of adult carabid beetles on below- and above-ground pests and fruit yield was examined in the laboratory and a two-year strawberry field study. In the laboratory, adults of Carabus nemoralis Muller, Nebria brevicollis (F.), Pterostichus algidus LeConte, Pterostichus melanarius (Illiger), and Scaphinotus marginatus Fischer (Coleoptera: Carabidae) consumed black vine weevil, Otiorhynchus sulcatus (F.) (Coleoptera: Curculionidae) eggs, larvae and/or pupae placed on the surface. The same five carabid species showed no impact or low removal rates of O. sulcatus larvae that had burrowed into the root of potted strawberry plants. In an assay with only P. melanarius, adults consumed O. sulcatus larvae placed on the soil surface more frequently than larvae buried 1.3 or 5 cm below. In a field study, the density of adult carabids, predominantly P. melanarius, was manipulated with augmented, exclusion, and open control plots (2 x 2 m). Manipulating carabid density had no impact on the removal of sentinel O. sulcatus larvae and pupae that were buried belowground which is consistent with laboratory observations. Increasing carabid density within augmented plots led to greater removal of red clover seeds, Trifolium pratense L., placed on the soil surface in the first year. Decreasing carabid density within exclusion plots resulted in fewer marketable fruits compared to control plots in both years. These results suggest that certain adult carabids may have limited impact belowground, and some beneficial impacts above-ground with pest control and crop protection.