46 NATURAL HISTORY OF GLOSSINA PALPALIS 



187-3 

 that month was 6-3. = 29*7, which is the " pupae 



D' o 



per female " figure for the month. 



If these figures are plotted out for the twelve months, 

 it is seen that the curve thus formed is inverse to the curve 

 of relative humidity. This may be a definite adaptation 

 to enable Glossina to tide over the drier months, which 

 are adverse to the adult fly. That is, during the drier 

 months (of lessened humidity) more pupae are deposited, 

 the pupa being resistant to a greater degree to adverse 

 climatic influences than is the perfect fly. 



Experiments were performed to test the vitality of pupae 

 exposed to various conditions of dampness or drought. 

 Batches of pupae were submerged in water daily for difiPer- 

 ent lengths of time, and it was found that daily submersion 

 for twelve hours on twelve successive days only destroyed 

 36 per cent, of the pupae, and that only 33 per cent, were 

 destroyed by four submersions of twenty-four hours, 

 with an interval between each of twelve hours. The 

 effects of continuous submersion were tried, and it was 

 found that a period of 108-120 hours is necessary to 

 destroy all the pupae in a batch. 



Flotation on the surface can be borne for eight days, 

 but ten days are fatal. 



Pupae were also put in a small wooden box covered 

 with one inch of earth, and the box was sunk in the ground 

 flush with the surrounding surface and left exposed 

 to the sun during the hottest hours of the day. A single 

 exposure up to six hours does not harm the pupae, but 

 if uncovered by earth a single hour is fatal. The effect of 

 repeated exposures on successive days was then tested : 

 two hours daily for three days made very little difference 

 to the pupae, but three hours daily for three days resulted 

 in only 2 per cent, of flies emerging ; six hours daily for 

 two days killed all. Lastly, alternate submersion and 

 exposure are fatal ; although a single submersion of 



