Assessing the potential impact of biological control of Plutella xylostella (diamondback moth) in cabbage production in Kenya

Abstract

This study assessed the potential economic impact of the introduction of Diadegma semiclausum, an exotic parasitoid of the diamondback moth ( Plutella xylostella, DBM), on cabbage production in Kenya. The study first established yield losses caused by DBM through two methods: measurements from farmer-managed fields and through farmers’ interviews. Crop losses were calculated at 31% from farmer-managed fields, and at 36% from farmer interviews. With a crop loss of 31%, yield loss was estimated at 6.8 tons/ha or US$ 452.9/ha, and at US$ 7.9 million per year for the whole country. Control costs as provided from the interviews, amounted to US$ 118.9/ha. The project costs amount to a net present value of US$ 1.2 million. Based on an annual cabbage production of 256,524 tons, a cabbage price of US$ 66.3/ton, a 30% abatement of yield losses, a 7.9% reduction in cost of production, a supply and a demand elasticity of 0.9 and −1.4 respectively, and an annual increase of consumption of 2.6%, the economic surplus produced by the release of the parasitoid was estimated at US$ 28.3 million for 25 years. Consumers were estimated to get 58% of the benefit and producers 42%. The benefit–cost ratio was estimated at 24:1, with an internal rate of return of 86%, indicating a high return to the investment.