Assessment of naturally occurring parasitism of diamondback moth in field using recruitment method

Abstract

The recent major outbreaks of diamondback moth, Plutella xylostella (Lepidoptera: Plutellidae), in cruciferous plants in Iran has led to attempts for sustainable pest management strategies, mainly based on the natural enemies. The present study aimed to investigate naturally occurring parasitism of P. xylostella in cabbage and cauliflower fields of central Iran. For this purpose, field studies were performed to identify parasitoids of P. xylostella, and to evaluate percentage parasitism of P. xylostella using the recruitment method in main cabbage-growing areas of Isfahan province in 2009. In present study, seven species of parasitoid wasps (five larval and two pupal parasitoids) and two species of hyperparasitoid wasps were determined. The parasitoids included the braconids Cotesia vestalis (Kurdjumov), Bracon hebetor Say and Apanteles sp., the ichneumonid Diadegma semiclausum (Hellen), and the eulophid Oomyzus sokolowskii (Kurdjumov) as larval parasitoids, and the ichneumonids Diadromus collaris (Gravenhorst) and Diadromus subtilicornis (Gravenhorst) as pupal parasitoids. In addition, the pteromalids Mokrzeckia obscura Graham and Pteromalus sp. were identified as the hyperparasitoids, which in turn parasitise C. vestalis. The most predominant species were C. vestalis and D. semiclausum with the proportional abundance of 0.43 and 0.42, respectively. Percentage parasitism varied significantly between host plants, but not between areas; the parasitised proportion of P. xylostella larvae fed on common cabbage was significantly greater than that on cauliflower (0.42 vs. 0.34). The mean percentage parasitism varied between 14.5 and 68.4 for different fields, and accounted for 37.4% of P. xylostella population on an average. The greatest parasitism was achieved by C. vestalis, D. semiclausum and O. sokolowskii, with a parasitism of 21.0, 12.9 and 3.5% of field populations of P. xylostella, respectively. These findings illustrated the important role of parasitoids for sustainable management of diamondback moth.