Identification of predation by spiders on the diamondback moth Plutella xylostella.

The diamondback moth (DBM), Plutella xylostella L. (Lepidoptera Plutellidae), is one of the most destructive cosmopolitan pests of brassicaceous crops, and spiders (Araneae) are important predators to control DBM in the fields. A specific DNA marker was developed for detecting predation on DBM by four species of spiders, Ebrechtella tricuspidata (F.), Pardosa astrigena Koch, Pardosa laura Karsch, and Pardosa pseudoannulata (Boesenberg et Strand). 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. This 275-bp sequence was not found in 16 other species of arthropods collected from crucifer fields. When the spiders were analyzed after they were fed a single fourth-instar P. xylostella, 50% of E. tricuspidata individuals were positive for the 275-bp PCR product up to 36 h after feeding. Likewise, the 275-bp PCR product was present in 60% of the individuals of P. astrigena, 70% of P. laura, and 70% of P. pseudoannulata up to 72 h after feeding on a single fourth-instar P. xylostella. A study in a cabbage and a rape field found that P. astrigena showed the highest incidence of positivity for the 275-bp PCR product, assayed by using primers of DBMITSF3/DBMITSR3; and the species of spiders and the two different fields were correlated with the positivity incidences of these spiders.