Canola, Brassica napus L., is a relatively new crop in South Africa. Several insect pests including diamondback moth (DBM), Plutella xylostella (L.) (Lepidoptera: Plutellidae) that attack cruciferous vegetables, also attack canola. A study was undertaken to determine seasonal phenology of DBM, composition, relative abundance and seasonality of its parasitoids on canola. DBM adults were monitored with synthetic sex-pheromone traps. Larval and pupal populations of DBM were monitored weekly for three years at Bapsfontein and Rietondale in Gauteng province. Samples of DBM larvae, pupae and parasitoid cocoons were collected and brought to the laboratory. Parasitoids that emerged were identified and their incidence recorded. Berlese funnel catches were used as an indicator to the accuracy of the visual counts.

The infestation level of DBM larvae was high from May to August in Rietondale, Pretoria, whilst in Bapsfontein it was high from September to December. There was a high correlation between pheromone trap catches and subsequent larval infestations in Bapsfontein. The pheromone traps indicated that DBM adults were present throughout the year. Berlese funnel catches indicated that a greater number of smaller larvae were missed during plant sampling. Parasitism often reached high levels, although not enough to reduce pest populations to below economic damage level. The following parasitoids emerged from field collected larvae, pupae and parasitoid cocoons: Cotesia plutellae (Kurdjumov) (Braconidae), and Apanteles eriophyes (Nixon) (Braconidae), both larval parasitoids; Diadegma mollipla (Holmgren) (Ichneumonidae), and Oomyzus sokolowskii (Kurdjumov) (Ichneumonidae), both larval-pupal parasitoids; Diadromus collaris (Gravenhorst) (Ichneumonidae) pupal parasitoids; Mesochorus sp. (Ichneumonidae) and Pteromalus sp. (Pteromalidae). Cotesia plutellae was the most abundant parasitoid occurring throughout the study.

For more information see:

Mosiane, S.M. 2001. Diamondback moth, Plutella xylostella (Lepidoptera: Plutellidae) and other insects of canola, Brassica napus in Gauteng Province, South Africa. MSc thesis, Rhodes University.

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