Control of Glossina longipennis (Diptera : Glossinidae) by insecticide-treated targets at Galana Ranch, Kenya, and confirmation of the role of G. longipennis as a vector of cattle trypanosomiasis

Glossina longipennis Corti was studied in Galana Ranch, Kenya over a four y ear period, in two areas (Tank E and Lali) where the species was abundant a nd other species were absent or scarce. There was active transmission of tr ypanosomiasis to cattle in both areas, the parasite species being Trypanoso ma vivax Ziemann and T. congolense Broden. Mean infection rates of the G. l ongipennis were 1.1% and 0.55% for T. vivax and T. congolense respectively at Tank E, and 0.88% and 0.15% at Lali. Experimental transmission studies s howed that cattle in fly-proof enclosures challenged with wild G. longipenn is collected from Galana became infected with both trypanosome species. A t setse control operation in one area (Tank E) using targets impregnated with deltamethrin in an oil formulation reduced the population of G. longipenni s by 98% over one year, despite evidence of re-invasion. Populations of G. longipennis in the other area (Lali) were relatively stable over the whole study period. The effect of tsetse control on the incidence of cattle trypa nosomiasis at Tank E was less clear than that on tsetse numbers, probably d ue to the lack of a sustained reduction in tsetse numbers. However, a signi ficant relationship was demonstrated between fortnightly incidence measurem ents and electric net catches of G. longipennis at Tank E. A further signif icant predictor of incidence was rainfall in the previous four to seven wee ks. This study confirms the importance of G. longipennis as a vector of bov ine trypanosomiasis in areas where it is the predominant tsetse present.