Problem Statement: The Diamondback moth Plutella xylostella, is a major crop pest which occurs mainly on crucifers (cabbages and kales) worldwide. The moth is a particular problem in East Africa, where crucifers are part of the daily diet and provide most of the vitamins and minerals for the poor segment of the population. Although an estimated $1 billion is spent on pesticides to control this species, it has developed resistance to almost all commercial pesticides.

Methods: As parasitation rates by native parasitoids are very low (<15%), the International Centre of Insect Physiology and Ecology (icipe) in Kenya developed a biological control programme, financed by the German Ministry for Economic Cooperation and Development. The parasitoid Diadegma semiclausum was considered on the basis of its success in South East Asia, but its taxonomic status was unclear. Due to previous misidentifications, Kenyan authorities would not allow a release unless it was shown beyond doubt that the exotic species was different to the local one and a more effective parasitoid. Molecular tools were used in addition to classical morphological tools to prove that the native Diadegma species from Kenya was different from the exotic D. semiclausum from Taiwan, which had been shown to be a much superior parasitoid of Diamondback moth.

Outcomes and Impact: A year after the release of D. semiclausum in Kenya it was established in the pilot sites, and parasitation rates had already increased (>40%). Permission for a general release was then issued in Kenya and more activities are planned in other east African counties to build on the promising results. In an ex-ante economic impact assessment conducted by the project for Kenya alone, cost / benefit ratio of 1:31 was predicted over a time period of 20 years.

Lessons: Biological control agents can provide highly cost-effective alternatives to pesticide use, particularly where target species have built up resistance. Molecular techniques can help taxonomists to differentiate between morphologically similar species and to identify effective biological control species.