Changes over twelve years in populations of Glossina pallidipes and Glossina longipennis (Diptera: Glossinidae) subject to varying trapping pressure at Nguruman, south-west Kenya

Abstract

AbstractLong term changes in the size of populations of the tsetse Glossina pallidipes Austen and G. longipennis Corti were monitored over a 12 year period at Nguruman in south-western Kenya. Tsetse populations were subject to droughts of varying intensity and, from 1987, to trapping, initially by a research organization, and later by a community-based development project. Populations were mainly sampled using odour-baited biconical traps, with data from other monitoring traps corrected accordingly. Mark–release–recapture studies were carried out to relate trap catches to absolute population size, and to quantify movement between subpopulations. Trypanosomiasis incidence rates in a herd of local cattle were also monitored for much of this period. Trap catches were shown to be well correlated with estimates of absolute population size, with no evidence of any seasonal change in trap efficiency. The intensity of trapping and level of seasonal immigration appeared to be the main determinants of population trends, with effective control being achieved when traps were well maintained. Movement between the two lowland subpopulations was shown to be greater for females, and to be inversely related to temperature. An analytical model was used to investigate the responses of a partially isolated population to trapping pressure. Predictions of a deterministic simulation model demonstrated that the observed changes are consistent with an adult trapping mortality of 4–8% per day, and immigration of 100,000 G. pallidipes females per month in the long rains (April and May), 5000 per month in the short rains (November), and about 500 per month during the dry seasons. Trypanosomiasis incidence in local cattle was greatly reduced during the period of community-based tsetse control. When tsetse were sampled exactly where the cattle were grazing, disease incidence was shown to be linearly related to G. pallidipes catches. Arguments for trap resistance and residual populations were examined, and found to be inconsistent with the data. The future for tsetse control by the Nguruman community is considered.