Molecular identification of interaction pathways between carabid beetles and slugs in alfalfa


Abstract: Global trade facilitates the intercontinental movement of cargo and thus increases thepotential introduction of exotic gastropods to new areas of the world. Hence, there is a growingneed to understand ecological interactions of newly introduced species with the native fauna.Furthermore, exotic slugs are of particular concern because yield losses to commodities plantedthroughout much of the continental United States are high and states such as Kentucky, whosehumid climate typically supports a high density of these species, have significant acreage offarmland planted to crops at risk of damage including alfalfa, soybean, wheat and corn. Giventhese concerns, and the high density of endemic natural enemies inhabiting these agroecosystems,it is essential to examine the mechanisms of predation, decipher the strength of interactionpathways and evaluate the role of predators in biological control. In 2008, over 1,000 specimensof three species of ground beetles (Carabidae) were collected from alfalfa and screened bypolymerase chain reaction using species-specific primers to identify the presence of DNA of theexotic slug Deroceras reticulatum. Feeding trials indicated that slug DNA was detectable inpredator guts for approximately 12 h and, significantly, during the month of June, 5% ofHarpalus pensylvanicus, 25% of Scarites quadriceps and 5% of S. subterraneus specimensscreened positive for D. reticulatum DNA. Drought conditions thereafter likely caused slugpredation rates to decrease as their availability to epigeal predators declined. This research hasenhanced our understanding of complex and emerging slug-carabid interactions in NorthAmerica and provides a valuable framework for future efforts in conservation biological control.

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