72 



at 20 C produced an average of 10.3% ± 7.6 (range 2-25%) 

 MB spores; those held at 32 C produced an average of 16.8% 

 ±6.8 (range 6-23%). Pupae exhibiting minimal clearing 

 of the occiput produced averages of 18.7% ± 14.0 (range 

 1.5-40%) and 24.4% ±3.7 (range 18.5-33.5%) at 20 and 32 C 

 respectively. Approximately 90% of the spores in these 

 latter two age groups appeared to be mature. 



The measurements of NMB spores from pupae reared from 

 larvae at 20, 28 or 32 C were, respectively, 3.0 ± 0.2 X 

 6.8 ± 0.3 mu, 3.0 ± 0.1 X 6.8 ± 0.3, and 3.0 ± 0.0 X 7.0 ± 

 0.4 mu. Obviously, there were no differences in NMB spore 

 sizes (MB spores were not produced at 20 or 32 C) . 



Neither MB or NMB spores were seen in tissue sections 

 of fat body of pupae reared at 20 or 32 C. Very few MB 

 spores were seen in sections of fat body of pupae reared 

 at 22.5 C. 



Discussion 



The development of NMB spores precedes the development 

 of MB spores, and NMB spores predominate in number. In 

 field colonies, MB spores typically constitute ca 25-40% 

 (occasionally fewer) of the spores from pupae in advanced 

 stages of infection (Jouvenaz and Hazard, 1978). The present 

 study has demonstrated that MB sporulation also occurs in 

 a more restricted range of temperature than NMB sporulation. 



The lower thermal limit of MB spore development appears 

 to be between 20 and 22.5 C. At 28 C production of MB spores 



