PAPERS ON ZOOLOGY 309 



wMch increase in size nntil they become confluent. (4) 

 The final stage is the ripening of the spores, which are a 

 dark, gray-olive in color, and which typically form a solid 

 layer from one to two millimeters thick over the entire 

 surface of the pupa. 



Time will not permit a discussion of the details of in- 

 dividual experiments, but a summary of the general re- 

 sults presents the following facts which seem especially 

 worthy of note : A. Even at optimum relative humidi- 

 ties, development of the fungus in these tests did not oc- 

 cur in either series of pupae at temperatures below 14^ 

 nor above 38" C. 5. At 35" C. aerial hyphae may appear 

 on the surface of a mature mummified specimen, but a 

 new crop of spores will not be formed. At this tempera- 

 ture the injected spores may infect and kill the insect 

 host, but the fungus can not propagate itself. C. The 

 most rapid development of the fungus, or the shortest 

 time observed between exjDosure to infection and the rip- 

 ening of a new crop of spores (17 days for the injected, 

 and 29 days for the dusted series), occurs at 30~ to 31° 

 C. D. Spores are produced in gi'eater abundance at tem- 

 peratures between 18° and 26° C, which appears to be 

 the optimum temperature range for this species of en- 

 tomogenous fungus. E. At optimum temperatures, con- 

 stant relative humidities below 80 per cent appear to be 

 prohibitive. At constant relative humidities between SO 

 per cent and 90 per cent infection does not occur in the 

 dusted series of pupae, and while the disease in the in- 

 oculated series will progress to the mmnmification stage, 

 the subsequent external development of the fungus and 

 especially the fonnation of spores is very scanty. Eela- 

 tive humidities between 95 per cent and 100 per cent con- 

 stitute the oiDtimum range for this species. 



It is needless to say that combinations of temperatures 

 between 18° and 26° C. with relative humidities be- 

 tween 95 per cent and 100 per cent of any considerable 

 duration are not common, especially during periods when 

 injurious insects are most abundant, unless it be in trop- 

 ical or sub-tropical regions or possibly in subterranean 

 habitats. Further investigations are imder way or pro- 



