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.
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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