A sampling bias model for odour-baited traps in relation to tsetse hunger cycle and population suppression

Eight progressive stages of midgut evacuation (MES), which reflect increasing degrees of hunger, were used to define the hunger cycle in tsetse. The distribution of flies in all eight MES in thriving tsetse populations, as well as in odour-baited trap catches, was modeled using exponential and β probability density functions, respectively. These distributions enabled derivation of the proportion (p) of a tsetse population that succumbs daily to a sampling device. This parameter proved useful for evaluating the bias of cow urine-baited NG2G trap samples of Glossina pallidipes, and for estimating trapping mortality and the required period and trap density for tsetse control. The higher the value of p, the less biased the sample and the higher the trapping mortality; the shorter the period, the fewer the number of traps required for achievement of tsetse control. Simulations based on field data and parameter estimates in the published literature predict that ICIPEʹs NG2G traps baited with cow urine may achieve up to an average of 97 and 98% reduction of G. pallidipes populations in 1 year. The traps may achieve up to a 98% reduction in 1 year, in 75% of suppression trapping campaigns. It will require about 2 years to achieve a 99.9% reduction in the fly population, given these parameters.