Identifying key cereal aphid predators by molecular gut analysis

We describe polymerase chain reaction (PCR) primers for gut analysis of aph id predators. The primers amplify aphid mitochondrial COII fragments rangin g in size from 77 to 386 bp. Using these primers, we were able to distingui sh six species of US Great Plains cereal aphids, including two congeners, R hopalosiphum maidis (Fitch) and R. padi (L.), and to detect them in extract s of coccinellid and chrysopid predators. We devised a protocol for derivin g half-lives of detectability for the DNA of a single aphid consumed by pre dators maintained under simulated field dietary and temperature conditions. Using this protocol and primers that amplify a 198-bp fragment, we determi ned statistically different half-lives of detectability for a single R. mai dis of 3.95 h in Chrysoperla plorabunda (Fitch) and 8.78 h in Hippodamia co nvergens Guerin. The detectability half-life for a 339-bp R. maidis fragmen t was statistically longer in C. plorabunda but not in H. convergens. The s ensitivity of the assay for the 198-bp fragment is 10(-7) aphid equivalents . For species-specific predator gut analysis, PCR is superior to monoclonal antibody technology, giving comparable detectability half-lives with lower expense, much shorter development times, and greater certainty of a succes sful outcome.