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

Abstract

AbstractGlossina longipennisCorti was studied in Galana Ranch, Kenya over a four year period, in two areas (Tank E and Lali) where the species was abundant and other species were absent or scarce. There was active transmission of trypanosomiasis to cattle in both areas, the parasite species beingTrypanosoma vivaxZiemann andT. congolenseBroden. Mean infection rates of theG. longipenniswere 1.1% and 0.55% forT. vivaxandT. congolenserespectively at Tank E, and 0.88% and 0.15% at Lali. Experimental transmission studies showed that cattle in fly-proof enclosures challenged with wildG. longipenniscollected from Galana became infected with both trypanosome species. A tsetse control operation in one area (Tank E) using targets impregnated with deltamethrin in an oil formulation reduced the population ofG. longipennisby 98% over one year, despite evidence of re-invasion. Populations ofG. longipennisin the other area (Lali) were relatively stable over the whole study period. The effect of tsetse control on the incidence of cattle trypanosomiasis at Tank E was less clear than that on tsetse numbers, probably due to the lack of a sustained reduction in tsetse numbers. However, a significant relationship was demonstrated between fortnightly incidence measurements and electric net catches ofG. longipennisat Tank E. A further significant predictor of incidence was rainfall in the previous four to seven weeks. This study confirms the importance ofG. longipennisas a vector of bovine trypanosomiasis in areas where it is the predominant tsetse present.