The diamondback moth,
Plutella xylostella (Lepidoptera: Plutellidae), is the most important insect pest of crops of the cabbage family throughout the world. The cost of its chemical control exceeds one billion US dollars annually. In many countries, the diamondback moth has become resistant to all synthetic insecticides used against it in the field and also to toxins from the bacterium
Bacillus thuringiensis. In South Africa, consumption of cabbage crops as a staple vegetable, especially in rural and peri-urban areas, is steadily increasing, and the pest status of the diamondback moth is rising.
The only method currently used by farmers in South Africa to control the diamondback moth is the application of synthetic pesticides. However, most resource-poor farmers cannot afford these insecticides. Affordable, alternative, non-chemical and sustainable control methods for the diamondback moth are under investigation, with the emphasis on biological control.
Twenty-three indigenous parasitoids associated with the diamondback moth have been recorded so far on cabbage in South Africa. The economic threshold level for chemical control of diamondback moth in cabbage was also determined. The large numbers of indigenous plants from the Brassicaceae in South Africa on which diamondback moth can develop, and the richness and diversity of the fauna of diamondback moth parasitoids, suggest that the pest may have originated in southern Africa.
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