21 



to fourth-ins tar larvae in a paste of finely powdered (mortar 

 and pestle) dry baby cereal and spore suspension. Infrabuccal 

 pellet-sized quantities of this preparation were placed 

 on the praesaepia of f ourth-instar larvae with a flattened 

 insect pin, and the larvae were held in a miniature nest 

 cell until pupation. Adult workers were provided to care 

 for these larvae ca 4 hours after feeding. When the larvae 

 pupated, 20 meconia were recovered and examined by phase- 

 contrast microscopy to determine whether spores had extruded 

 their polar filaments. 



A suspension of NMB spores only was obtained by selecting 

 diseased pupae which, on the basis of pathognomonic signs, 

 were estimated to harbor some mature NMB spores but no mature 

 MB spores (NMB spore development precedes MB spore development) . 

 Wet squashes of these pupae were examined individually by 

 phase-contrast microscopy, and those that were free of mature 

 MB spores were washed from the slide, pooled, and cleaned 

 and concentrated by centrifugation. An examination of 10,000 

 spores individually in a diluted aliquot (0-5 spores/field) 

 and careful scanning of the concentrated suspension confirmed 

 the absence of MB spores. 



The suspension of NMB spores was mixed with boiled 

 egg yolk and fed to a small healthy colony of S^. geminata . 

 After 20 days, 25 pupae in advanced infection were individually 

 homogenized in ca 0.5 ml water and examined by phase-contrast 

 microscopy (0-6 spores/field) to determine the ratio of the 



