Termite-induced injuries to maize and baby corn under organic and conventional farming systems in the central highlands of Kenya

Publication Type

Journal Article

Journal Name

Population Ecology

Publication Date

10-1-2008

Abstract

A two-host-two-parasitoid model was constructed to assess the effects of the introduced larval parasitoid, the braconid Cotesia flavipes, on its primary target host, the invasive crambid Chilo partellus, and on secondary host species, in inter-specific competition with Cotesia sesamiae, the main native parasitoid species of stemborers in Kenya. The model assumed that: (1) there was no host discrimination by either parasitoid species; (2) Cotesia flavipes was the superior competitor that out-competed Cotesia sesamiae when the host was suitable; and (3) Cotesia flavipes could only develop in an unsuitable host if it had been previously parasitized by Cotesia sesamiae. Model parameters were estimated from surveys conducted in Kenya and from laboratory experiments. Different scenarios of host and parasitoid species composition and host suitability occurring in the different ecological zones in Kenya were analyzed. Results indicated that: (1) the coexistence of stemborer host populations are determined by their population growth rates, the degree of aggregation of the parasitoids and their searching efficiency; (2) in the regions where both the invasive and the predominant native host species were suitable to either parasitoid species, stemborer densities would be reduced to and controlled at low densities, and Cotesia flavipes would become the dominant parasitoid species. However, the extinction or predominance of the native stemborer species depends on the ratio of the growth rates of exotic and native stemborers and their relative searching efficiencies; and (3) if the native host species was acceptable but unsuitable to Cotesia flavipes, the parasite would not become established. © 2008 The Society of Population Ecology and Springer.

Keywords

Ecological zones, Exotic and native host species, Inter-specific competition, Pyralid and noctuid borer species, Suitable and unsuitable host species, Two-host-two-parasitoid model

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