Parasitism of Plutella xylostella (Lepidoptera: Plutellidae) in southern Pakistan
Keywords:
biological control, Oomyzus sokolowskii, Cotesia plutellaeAbstract
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.
Resumen
Las larvas de la palomilla de dorso de diamante, Plutella xylostella (L.) (Lepidoptera: Plutellidae) causan pérdidas económicas severas a los vegetales crucíferos en Pakistán. Se realizaron estudios desde el 2007 hasta el 2010 para identificar y evaluar la abundancia de parasitoides que atacan a P. xylostella en campos comerciales de coliflor tratados con insecticidas en el sur de Pakistán. En total, se encontraron 6 especies de parasitoides que atacan las larvas y pupas de P. xylostella. Estos incluyen el parasitoide larval, Cotesia plutellae Kurdjumov (Hymenoptera: Braconidae); Cotesia sp. (Hymenoptera: Braconidae); Diadegma sp. (Hymenoptera: Ichneumonidae); un parasitoide larval-pupal, Oomyzus sokolowskii Kurdjumov (Hymenoptera: Eulophidae); un parasitoide de la pupa, Diadromus collaris Gravenhorst (Hymenoptera: Ichneumonidae); y un parasitoide de la pupa, Brachymeria excarinata Gahan (Hymenoptera: Chalcididae). Cotesia plutellae proporcionó el 2.3 a 52.2% de parasitismo, seguido de O. sokolowskii con un 2.1 a 6.7% de parasitismo. El promedio del parasitismo causado por Cotesia sp. fue del < 5%. Los parasitoides restantes fueron escasos con un < 0,5% de parasitismo. Estudios adicionales sobre el parasitismo por O. sokolowskii mostraron que había una correlación positiva significativa entre el peso pupal de P. xylostella y el número de parasitoides que emergían de una pupa. Más del 50% de las pupas parasitadas por P. xylostella soportaban de 6 a 10 adultos de O. sokolowskii por pupa. Se deben realizar esfuerzos para preservar estos enemigos naturales a través de prácticas culturales y el uso de insecticidas no persistentes para permitirles funcionar de manera más efectiva en un programa integrado de manejo de plagas.
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