The pest status of diamondback moth (DBM), Plutella xylostella (L.)
(Lepidoptera: Plutellidae), 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 each week
continuously for two years on unsprayed cabbage plots. Adult populations were
also monitored continuously for two years with 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-December. Even when infestations in the field were low, a
high percentage of plants was infested, indicating a regular distribution of
progeny. 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 were found to be associated with DBM: 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 high 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.
For more information see:
Kfir, R. 1998. The diamondback
moth with special reference to its parasitoids in South Africa. In: Management
of Diamondback Moth and other Crucifer Pests. Ed. Sivapragasam et al.
MARDI Press.
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