85 



eventually the pupa ruptures and is cannibalized by workers. 

 The histopathological basis of these signs was not understood, 

 nor was the exact mode of transmission of the parasite. 

 An effort was made to extend our limited knowledge 

 of B^. dimorpha in the areas outlined above. In addition, 

 the effect of temperature on spore dimorphism was investi- 

 gated, and certain aspects of the life cycle and morphology 

 of the parasite were reexamined. The conclusions reached 

 in this study are summarized below. 



1. It was experimentally confirmed that B. dimorpha is 

 a dimorphic species, producing two morphologically distinct 

 types of spores, and not a dual infection of two species 



of microsporidia. 



2. Only NMB spores are infective; unextruded MB spores 

 are expelled in the meconium upon pupation. 



3. The intracolonial cycle of transmission of B. dimorpha 

 infection is from ruptured, diseased pupae to f ourth-instar 

 larvae via the adult workers, who act as mechanical vectors. 



4. Adult workers do not ingest spores into the crop, 

 but divert them to the infrabuccal cavity where they are 

 formed into infrabuccal pellets with particulate food material. 



5. Only f ourth-instar larvae are vulnerable to infection. 



6. Burenella dimorpha is host-specific for S^. geminata . 

 Infections in S^. invicta and S^. richteri do not persist 



in the colony. 



