68 



Histology 



Tissue specimens from gasters of pupae held at 20 or 32 C 

 until infection was very advanced were fixed, stained with 

 heavy metals embedded in Spurr-Quetol resin, sectioned, and 

 examined by phase-contrast microscopy. The details of these 

 procedures are given in the section on host pathology. 



Results 



The development of MB spores was inhibited in pupae 

 held at high (32 or 35 C) or low (20 C) temperature. At 

 28 C, the temperature at which S_. geminata colonies seem 

 to live best in my insectary, an average of 35.9% ± 2.6 

 of the spores in 25 pupae were of the MB type (Table 3). 

 Jouvenaz and Hazard (1978) stated that MB spores typically 

 constitute ca 25-40% of the spores in diseased pupae collected 

 in the field. 



Only 10 of the pupae held at 35 C survived to an advanc- 

 ed stage of infection. These pupae were devoid of MB spores, 

 and a small number (ca 2%) of the NMB spores from these 

 pupae were morphologically aberrant (pairs of spores fused 

 laterally or in tandem, Y-shaped or triangular spores, giant 

 spores, etc.). Thirty-five degrees appears to be very near 

 the upper thermal limit of survival for host and parasite. 



Twenty- two of the 25 pupae held at 32 C were negative 

 for MB spores. Only four immature MB spores were among 

 the 600 spores from the remaining three pupae (200 spores 

 from each specimen were examined) , 



