IMPACT ASSESSMENT OF AN EXOTIC PARASITOID ON STEMBORER (LEPIDOPTERA) POPULATION DYNAMICS IN KENYA

Abstract

A ratio-dependent host–parasite interaction model with a linear trend was developed to analyze the impact of the exotic parasitoid Cotesia flavipes (Cameron) (Hymenoptera: Braconidae) on stemborer population dynamics in the southern coastal area of Kenya. The time dependence of the host and that between the host and parasitoid were tested using autocorrelation and cross-correlation functions. The criterion for measuring the parasitoid impact was the difference between the model predictions with and without the parasitoid. The results indicated that the suppressive impact of the parasitoid on stemborer densities began in the short rains season of 1997–1998 in the northern part of the coast zone but was only seen in the southern part of the coast beginning with the long rains season of 1999. The density reduction of the total stemborer complex, which includes one alien and two native species, by C. flavipes was 1.05 ± 0.25 larvae per plant in the north coast and 0.62 ± 0.58 larvae per plant in the south coast during the long rains season of 1999. The reduction of the exotic stemborer Chilo partellus (Swinhoe) (Lepidoptera: Crambidae) by C. flavipes was 0.99 ± 0.25 larvae per plant in the north coast in the long rains season of 1999, or a 52.94 ± 13.37% decrease of the C. partellus density. In the south coast, the reduction was 0.83 ± 0.41 larvae per plant or ∼33.07 ± 16.33% decrease in the C. partellus density.