Parasitism of Plutella xylostella (Lepidoptera: Plutellidae) in Southern Pakistan

Abstract

Larvae of diamondback moth, Plutella xylostella (L.) (Lepidoptera: Plutellidae) cause severe economic loss to crucifer vegetables in Pakistan. Studies were conducted from 2007 to 2010 to identify and assess the abundance of parasitoids attacking P. xylostella in commercial, insecticide-treated cauliflower fields in southern Pakistan. In total, 6 parasitoid species were found attacking larvae and pupae of P. xylostella. These included the larval parasitoid Cotesia plutellae Kurdjumov (Hymenoptera: Braconidae); Cotesia sp. (Hymenoptera: Braconidae); Diadegma sp. (Hymenoptera: Ichneumonidae); a larval-pupal parasitoid Oomyzus sokolowskii Kurdjumov (Hymenoptera: Eulophidae); a pupal parasitoid Diadromus collaris Gravenhorst (Hymenoptera: Ichneumonidae); and a pupal parasitoid, Brachymeria excarinata Gahan (Hymenoptera: Chalcididae). Cotesia plutellae provided 2.3 to 52.2% parasitism, followed by O. sokolowskii with 2.1 to 6.7% parasitism. The average parasitism caused by Cotesia sp. was < 5%. The remaining parasitoids were scarce with < 0.5% parasitism. Additional studies on parasitism by O. sokolowskii showed that there was a significant positive correlation between P. xylostella pupal weight and the number of parasitoids emerging from a pupa. More than 50% of P. xylostella parasitized pupae supported 6 to 10 O. sokolowskii adults per pupa. Efforts should be undertaken to preserve these natural enemies through cultural practices and the use of soft insecticides to allow them to function more effectively in an integrated pest management program.