a1 Entomologist, Tsetse Investigation, N. Nigeria.
1. There is considerable seasonal variation in the longevity of G. submorsitans and G. tachinoides, and these variations are negatively correlated with the fluctuations in the maximum temperature curve, i.e., as the temperature rises longevity decreases, as the temperature falls so longevity increases.
2. The cycle is as follows:—The rains commence and temperature falls, longevity increases and remains high throughout the rains. The wet season ends, temperature rises and longevity descreases. The cold spell intervenes and longevity becomes maximal. The cold weather ends, the temperature soars up and longevity becomes minimal, remaining low until the new rains commence.
3. Maximum temperature is considered to be the dominant factor; favourable humidity cannot increase longevity unless the maximum temperature is favourable.
4. The oldest individuals occur in the rains, but the average longevity is highest in the cold season, when both temperature and humidity are favourable.
5. In both species females tend to live longer than males.
6. In the field G. tachinoides males appear to live rather longer than the males of G. submorsitans.
7. It is doubtful whether wild flies of either species live much more than 2½ to 3 months under the most favourable conditions; it is probable that in the hottest weather longevity is curtailed to a month or less, and that the production of puparia is seriously affected when the rains are late and the hot weather is prolonged.