Spatial and temporal distribution of tsetse fly trap catches at Nguruman, southwest Kenya

Spatial and temporal dynamics of rapidly growing populations of tsetse flies at Nguruman, southwest Kenya during 1993-1995, were investigated, following six years of intensive population suppression with traps over a c. 100 km2 area. The two tsetse species present were randomly distributed in the short rainy season, but were aggregated in the dry and long rainy seasons. Maximum temperature was the dominant weather factor associated with the degree of aggregation. Trends in catches at 20 fixed sites along an 18 km north-south axis were weakly correlated between locations, possibly representing population sub-structuring. In particular, trends in population change were poorly correlated between the area with a long history of trapping suppression in the south and the area with a more recent history of suppression in the north. On a micro-geographic scale, correlations among paired trap catches were clearly related to geographical proximity for Glossina pallidipes Austen (r2 = 0.55); whereas this relationship was quite weak for Glossina longipennis Corti (r2 = 0.12). Positive correlations among trap catches were significant for sites separated by less than c. 3.8 km (G. pallidipes) or 4.8 km (G. longipennis). These results suggest the existence of different population substructures in the two species on a relatively small geographic scale.