Using molecular methods to analyze ground beetle (Carabidae) gut contents for evidence of predation on lowbush blueberry pests

Generalist predators provide an agroecosystem service if they consume plant pests.  Ground beetles (Carabidae) that are common during spring in lowbush blueberry fields were tested as predators of blueberry spanworm and blueberry flea beetle using molecular analysis of gut contents.  A ~600 bp fragment of the cytochrome oxidase I mtDNA was sequenced, and species-specific primers amplifying 207 bp for spanworm and 279 bp for flea beetle were designed and tested.  In laboratory feeding trials, median detection time (50% of samples testing positive) of spanworm and flea beetle DNA in the guts of Poecilus lucublandus and Pterostichus mutus was 27 – 32 h but was less than 4 h for spanworm DNA in the guts of Carabus nemoralis.  In a field where pests exceeded economic thresholds, 22 and 8% of P. lucublandus and P. mutus respectively tested positive for spanworm DNA, and 39 and 20% of P. lucublandus and P. mutus respectively tested positive for flea beetle DNA.  In a second field where spanworm was below threshold, only one P. mutus and no P. lucublandus or C. nemoralis tested positive for spanworm DNA.  Ground beetles consume lowbush blueberry pests, but predation rates may be related to pest abundance.