Biological control of cereal stem borers in Kenya: A cost benefit approach

Abstract

Lepidopteran stem borers are the key pests of maize in Sub-Saharan Africa. In the lowland tropics, dry mid-altitude, dry transitional and the moist mid-altitude zones of Kenya, the invasive crambid Chilo partellus (Swinhoe) (Lepidoptera: Crambidae) causes up to 73% yield loss. The International Centre of Insect Physiology and Ecology (ICIPE) started a biological control (BC) program in 1991 to control stem borers in subsistence agriculture in Africa with emphasis on classical BC of C. partellus. The project released the braconid larval parasitoid Cotesia fl avipes Cameron (Hymenoptera: Braconidae) in 1993 in coastal Kenya, where it got established and spread to other regions. This study assesses the economic impact of the introduced parasitoid. Temporal data on percentage parasitism by the introduced parasitoid and on stem borer density were collected between 1995 and 2004. Socioeconomic data was collected through administration of questionnaires to 300 farmers. Economic impact of the project was calculated as the value of the yield loss abated by the parasitoid based on a model of expected stem borer density and parasitism level. Average annual parasitism increased linearly from the time of introduction to reach 20% parasitism by 2004. The net reduction in total stem borer density over the last 10 years was 33.7%, thus abating 47.3% of yield loss. The region will accumulate a net present value of US $ 183 million in economic benefi ts in 20 years since release of the parasitoid. Introduction of other parasitoid species targeting the egg and pupal stages of the stem borer life cycle stages would be required for biological control to push yield loss by stem borers to an insignifi cant level. Résumé. Contrôle biologique des foreurs des céréales au Kenya : une approche économique. Les lépidoptères foreurs de graminées sont des ravageurs importants du maïs en Afrique subsaharienne. Dans les zones de faibles et moyennes altitudes du Kenya, le foreur exotique Chilo partellus (Swinhoe) (Lepidoptera : Crambidae) a causé jusqu'à 73% de perte de rendement. Le Centre international pour l'étude de la physiologie et de l'écologie des insectes (ICIPE, son abréviation anglo-saxonne) a initié en 1991 un programme de lutte biologique classique pour lutter contre ce ravageur. Ce programme a permis la libération en 1993 d'un parasitoïde braconide, Cotesia fl avipes Cameron (Hymenoptera : Braconidae), dans la région côtière du Kenya, où il s'est établi et à partir de laquelle il a colonisé d'autres régions. Cette étude détermine l'impact économique de l'introduction de ce parasitoïde. Des données temporelles sur le pourcentage de parasitisme et sur la densité de foreurs ont été collectées entre 1995 et 2004. Les données socio-économiques ont été obtenues à l'aide d'un questionnaire diffusé auprès de 300 fermiers. L'impact économique a été calculé à partir des données de perte de rendement inférées par un modèle d'estimation de la densité de foreurs et du taux de parasitisme. Le niveau moyen de parasitisme a augmenté linéairement au ...

Assessing the long-term welfare effects of the biological control of cereal stemborer pests in East and Southern Africa: Evidence from Kenya, Mozambique and Zambia

“…This study explored the implications of using an ecologically based host-parasitoid interaction on the welfare of communities in East and Southern Africa, and showed that the ecosystem service provided by beneficial insects was advantageous to farmers as well as consumers. To our knowledge, no comparable empirical studies on ex-post economic impact of the icipe classical biological control programme on cereal pests has been undertaken or published, but the cost-benefit analysis provided by Kipkoech et al (2006) is a reference point in such a discussion. The cited exante analysis predicted the benefit-cost ratio to reach 19:1 by the end of the 20-year period for maize in coastal Kenya.…”

“…Almost all the studies emphasized the first biological control agent that was released, Cotesia flavipes (Cameron) and focused on its short-term assessment (10 years after release), but economic assessments on the real social advantage were not carried out. Kipkoech et al (2006) to some extent assessed the economic advantages of the natural enemies released using cost-benefit analyses based on yield loss reduction and predictions of parasitism levels and pest densities. The latter ex-ante study lacked results from exclusion experiments, which help in strengthening impact evaluations.…”

Cost effectiveness of biological control of invasive mole crickets in Florida pastures

“…Comparing the geographical distribution of maize yields with release rates of Cotesia flavipes Cameron (Hymenoptera: Braconidae) over 20 years in Kenya, Africa, Kipkoech et al (2006) estimated a BCR of 19:1 due to parasitism of the stem borer, Chilo partellus (Swinhoe) (Lepidoptera: Crambidae). In this study, reductions in yield were estimated using established pest density-yield loss functions rather than actual on-farm data.…”

Distribution and extent of Cotesia Flavipes Cameron (Hymenoptera: Braconidae) Parasitism in Northeastern Ethiopia

“…8 Another indication of success was the positive economic impact associated with the introduction. 9,10 In Ethiopia, Cot. flavipes was recorded for the first time in 1999 by Emana et al, without being released.…”