John W Hargrove, Faikah Bruce, John Van Sickle
Using novel methodologies and ovarian dissection, we constructed life histories for ~90,000 female Glossina pallidipes and G. m. morsitans collected in Zimbabwe (1988-1999). Temperature-dependent development rates were used to estimate, for each fly, the dates spent as an oocyte, egg, larva, pupa - and adult in each ovarian category. This enabled analysis of relationships between wing and egg lengths of field-captured adults - and mean environmental conditions prevailing when these lengths were being determined, during oogenesis for eggs, and oogenesis plus pregnancy for wings. Lengths all oscillated seasonally with well-marked minima in the hot-dry season, when selection against small individuals continued for some weeks after emergence. Lengths were negatively associated with temperature and positively with Normalized Difference Vegetation Index (NDVI), which measures plant health, density, and vigor. Multiple linear regression models had R2 values of 0.68 and 0.66 for the means of egg and wing lengths, respectively, of flies pooled weekly in G. pallidipes. Corresponding R2 values were 0.53 and 0.56 for monthly pooling in G. m. morsitans. Mean wing length in G. pallidipes also increased with increasing rainfall. Mean egg lengths increased with maternal wing length, were shorter in primiparous flies but changed little thereafter. Factors reflecting moisture, heat and vegetative growth influence tsetse size, survival and abundance indirectly, through effects on vertebrate host availability and feeding risk. Models developed using flies captured after November 1991 accurately predict, with no further calibration, mean egg and wing lengths of flies captured before November 1991. The models facilitate true predictions of future changes in mean fly size based on readily available meteorological data, benefiting vector and disease control efforts in predicting climate-related changes in the vigor of tsetse populations. This aids proactive identification of priority areas for monitoring and control efforts, improving cost-efficacy of tsetse and trypanosomiasis control. [295 words].