Seasonal Variations in the Mean Size of Tsetse Flies

Abstract

The mean size of the males of the three tsetse speciesGlossina pallidipes,G. morsitansandG. swynnertoniis negatively correlated with the mean 2 p.m. saturation deficit of 2 months before.The correlation is highest (—0·90) forG. pallidipes, the largest species, and lowest forG. swynnertoni, the smallest. The variation coefficient of mean vein length also is highest forG. pallidipesand lowest forG. swynnertoni.The reason for the apparent 2 months' lag in the effect of saturation deficit on size of flies is that the mean male pupal period is 35 days in Shinyanga (23°C.) and the mean age of males measured is 3–4 weeks. If 1 month's lag is tried, the correlation forG. pallidipesdrops from —0·90 to —0·32, and with no lag at all it is —0·24. The correlation with maximum temperature of 2 months earlier is insignificantly lower than that with saturation deficit; it is —0·79 forG. pallidipes.