The diamondback moth with special reference to its parasitoids in South Africa

The pest status of diamondback moth (DBM), Plutella xylostella (L.) (Lepidoptera: Yponomeutidae), in South Africa is lower than in other countries with similar climates. A project was initiated to investigate possible reasons for this. Larval and pupal populations of DBM were monitored weekly for two years on unsprayed cabbage plots. Adult populations were also monitored continuously for two years using synthetic sex-pheromone traps. Samples of DBM were taken to the laboratory and parasitoids that emerged were identified and their incidence determined. Moths, larvae and parasitoids were active throughout the year. Infestations were low from January to September and high during October to December. Even when infestations in the field were low, a high percentage of plants was infested, indicating a regular distribution of DBM in the sample plots. In general, parasitism of DBM larvae and pupae was high (reaching 90– 100%) except in the winter months of June-August when it was low. Twenty one species of parasitoids and hyperparasitoids were reared from DBM larvae and pupae: the egg-larval parasitoids Chelonus curvimaculatus Cameron and Chelonus sp. (Braconidae); the larval parasitoids Apanteles eriophyes Nixon, Cotesia plutellae (Kurdjumov), Habrobracon brevicornis (Wesmael) (Braconidae) and Peribaea sp. (Tachinidae); the larval-pupal parasitoids Diadegma sp., Itoplectis sp. (Ichneumonidae) and Oomyzus sokolowskii (Kurdjumov) (Eulophidae); the pupal parasitoids Brachymeria sp., Hockeria sp. (Chalcididae), Diadromus collaris Gravenhorst (Ichneumonidae) and Tetrastichus howardi (Olliff) (Eulophidae); and the hyperparasitoids Aphanogmus fijiensis (Ferrière) (Ceraphronidae), Brachymeria sp., Hockeria sp, Proconura sp. (Chalcididae), Mesochorus sp. (Ichneumonidae), Pteromalus sp. (Pteromalidae), Eurytoma sp. (Eurytomidae) and Tetrastichus sp. (Eulophidae). The large number of indigenous plants from the Brassicaceae, the many species of DBM parasitoids and a bisexual form of the parasitoid D. collaris in South Africa suggest that DBM might have originated in southern Africa.