A DNA marker to identify predation of Plutella xylostella (Lep., Plutellidae) by Nabis kinbergii (Hem., Nabidae) and Lycosa sp (Aranaea, Lycosidae)

Predators are important biotic factors in the population dynamics of the diamondback moth, Plutella xylostella. A specific DNA marker was developed to detect P. xylostella in the gut contents of two polyphagous predators, Nabis kinbergii and Lycosa sp. A distinct 275-bp product was amplified by polymerase chain reaction (PCR) from the internal transcribed spacer (ITS-1) of the ribosomal gene of P. xylostella, but not from 11 other arthropod species collected from Brassica fields in South Australia. Fortuitously, the primer set could also amplify DNA products from two species and three varieties of Brassica plants, with the fragment size about 600 bp. When N. kinbergii was analysed after feeding a single fourth instar P. xylostella, 67% of individuals were positive with the 275-bp PCR product up to 16 h after feeding. Likewise, the PCR product was detected in 80% individuals of Lycosa sp. up to 72 h after feeding on a single fourth instar P. xylostella larva. Initial tests of samples collected from the field showed that the predation incidences for both N. kinbergii and Lycosa sp. determined by the 275-bp fragment corresponded to the density of P. xylostella in the field.