20 



determine whether spores were ingested or diverted to the 

 infrabuccal cavity (microsporidian spores are visible in 

 slightly compressed, intact fire ant body segments at a 

 magnification of 300X) . Heads of these workers 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. Eight fresh infrabuccal pellets were removed 

 from the praesaepia of larvae and examined by phase micro- 

 scopy for spores. 



After 24 hours, 109 f ourth-instar larvae were removed 

 from the nest and held in a miniature nest cell with conspe- 

 cific workers that had not been exposed to B. dimorpha . 

 These workers functioned as nurses (immatures held in isola- 

 tion from adults are quickly attacked by fungi) . After 

 21 days these immatures (now pupae) were examined for infec- 

 tion. A group of 79 prefourth (primarily third) instar 

 larvae were also removed from the same nest and held in 

 a similar manner until they eclosed as adults. 



A suspension of mature spores of both types was prepared 

 by homogenizing diseased pupae in distilled water with a 

 glass tissue grinder and centrifuging the extract in a dis- 

 continuous Percoll gradient (100%, 75%, 50%, and 25%) for 

 20 minutes at ca 10,000 g (Jouvenaz, 1981). This procedure 

 produced a clean suspension of spores of both types, almost 

 all of which appeared to be mature. These spores were fed 



