Diamondback moth (Plutella xylostella L.) (Lepidoptera: Plutellidae) and its parasitoids in Ethiopia

Surveys were carried out to determine the geographic distribution and intensity of Diamondback moth (DBM), and its parasitoids on brassica producing areas of Ethiopia in 2001. A multivariate ANOVA, principal component and cluster analyses, was used to analyze nine variables (DBM density, Parasitism by different parasitoid species, cropping systems, pesticide use systems and altitude) measured in 194 brassica fields of thirteen different regions. Principal component analysis showed that the first two of the nine principal components accounted for 70% of the variation in the data set. Higher DBM intensity was associated with pesticide usage and higher overall parasitism with intercropping system. Cluster analysis using Ward's Minimum Variance method clustered the thirteen regions in to four. Dendrogram and Geographic Information System (GIS) techniques were used to depict the clusters. Several parasitoid species have been recorded of which three species were important both in distribution and level of parasitism. These include Oomyzus sokolowskii (Hymenoptera: Eulophidae), Diadegma spp (Hymenoptera: lchneumunidae), and Cotesia plutellae (Hymenoptera: Braconidae). Over all parasitism ranged from 3.6 to 58.2% by regions. C. plutellae and Diadegma spp. are largely confined to the south western part of Ethiopia where insecticide use is very minimal. On the other hand 0. sokolowskii is mainly distributed in relatively heavy insecticide use areas of the Rift valley and northern Ethiopia; its presence in southwestern Ethiopia is negligible. (Résumé d'auteur