expelled, and fed to f ourth-instar larvae only. The intra- 

 colonial cycle of infection is thus from ruptured, diseased 

 pupae to fourth- instar larvae via the adults, who are mechan- 

 ical vectors. The binucleate, nonpansporoblast membrane- 

 bounded (NMB) spores are infective perorally for larvae; the 

 uninucleate, pansporoblast membrane -bounded (MB) spores are 

 not infective, and their function is unknown. These spore 

 types are tissue specific: NMB spores develop from disporous 

 sporonts in the hypodermis; MB spores develop in octets from 

 multinucleate sporonts in the fat body. 



The development of MB spores is temperature-dependent. 

 The lower thermal threshold for MB spore development is 

 between 20 and 22.5 C; the upper thermal threshold is below 

 32 C. A hypothesis is advanced that these limits are set by 

 the stability of an enzyme(s), and that the physiological 

 function blocked in MB sporulation is meiosis. 



Burenella dimorpha has two cycles of merogony (vegetative 

 multiplication). The meronts of the first cycle were originally 

 described as uninucleate cells that become binucleate and divide. 

 However, these nuclei are actually pairs of nuclei in a diplo- 

 caryotic arrangement. 



Surface structure has been seen for the first time in MB 

 spores. The surface of NMB spores is smooth. 



X 



