A NUTRITIONAL STUDY OF INSECTS 



11 



the larvae pupated. Apart from visible growths, the ster- 

 ility of the tube was tested by introducing loops full of the medium 

 on which larvae were working or had pupated into a sterile tube 

 of one of the following media; potato agar, banana agar, Pasteur's 

 agar, nutrient gelatine, nutrient bouillon and yeast agar. One 

 or all of these media w^ere used to test the environment of the 

 larvae for the presence of microorganisms (fig. 18). Usually 

 crushed adults, pupae, or larvae were also introduced into the 

 test culture tube. The method of inoculation was by stab or 

 streak; in the former case semianaerobes could develop. Ba- 

 nana agar was used most often, as it more nearly resembles the 

 natural environment of the fly and its associated organisms and 

 also can support vigorous growths of a large flora. ^ 



TABLE 3 



Smears of the media were examined after staining in the usual 

 manner with eosin or Loeffler's methylene blue. This examina- 

 tion was made with a 1.6 mm. Zeiss objective. Fresh smears 

 were examined, before staining, with dark and light field 

 illumination. 



B. Food of Drosophila. a. Growth of sterile larvae on ster- 

 ile fruit. From the foregoing experiments it is clear that yeast 

 is always present in the habitat of Drosophila larvae and is 

 usually imported into sterile media on the body of the adult or 

 pupa. Pupae and eggs do not contain living yeasts and any 

 yeasts on the external body surface can be killed by alcohol. 



* For example, Cocobacillus acridiorum, Bacillus prodigiosus, B. coli, B. aceti, 

 Streptococcus dispar, Saccharomycetes cerevisiae, S. ellipsoideus, S. anomalus, 

 Penicilium glaucum, Rhizopus nigricans, Aspergillus, Fusarium, Gliocladium, 

 etc. 



