70 



The development of MB spores was completely inhibited 

 in 25 pupae held at 20 C. A few immature MB spores were 

 found in pupae held at 22.5 C, indicating that the lower 

 thermal threshold of MB sporulation is between 20 and 22.5 C. 



Pupae reared from larvae at 20 and 28 C produced similar 

 numbers of NMB spores (Table 4). Pupae reared at 32 C produced 

 ca 75% as many spores per pupa and ca 60% as many spores per mg 

 bodyweight as did those reared at 28 C. 



The inhibitory effect of temperature on MB sporulation 

 in pupae placed at high or low temperature at comparable 

 ages was essentially the same (Table 5). Specimens placed 

 at 20 or 32 C as larvae or larvaform pupae (a total of 40 

 specimens) were negative for MB spores. Of the 10 specimens 

 placed at 20 C as early pupaform (lacking visible eye develop- 

 ment) pupae, five had no MB spores, two had one MB spore 

 each, two had two MB spores each, and the remaining pupa 

 had seven MB spores among the 200 spores that were examined. 

 Of the 10 specimens placed at 32 C as early pupaform pupae, 

 nine had no MB spores and the remaining pupa had only one 

 MB spore among the 200 spores. Thus, mean spore production 

 by this age group was less than one percent at either tempera- 

 ture. 



The production of MB spores in pupae that had developed 

 eyes to the extent that diagnosis of disease was possible 

 at the time they were placed at 20 or 32 C was lower than 

 in those reared at 28 C for their entire life. Those held 



