PARASITES AND ENEMIES OF DROSOPHILA. 17 



run through a "potato ricer," and then added to the agar solution. 

 Some workers add sodium hydroxide or carbonate to the mixture, but 

 it is best not to add enough to cause an alkahne reaction to Htmus. 

 While still hot the solution is poured into the culture bottles and 

 allowed to harden. Half-pint milk-bottles are very convenient for 

 this purpose. About 50 c. c. of banana agar to a bottle will give good 

 results. A very little powdered yeast is sprinkled over the surface of 

 the agar in each bottle. A piece of absorbent paper (paper toweling 

 is usually used) a few inches square is added, and the bottle is stoppered 

 with cotton. The flies may be introduced as soon as the bottle cools; 

 the bottle should not be kept longer than 48 hours before using. 



This culture medium has been found very favorable for many 

 species. Drosophila melanogaster, D. simulans, D. ohscura, D. funebris, 

 D. immigrans, D. virilis, and D. willistoni have all been bred on it 

 very extensively in pairs. Mass-cultures of numerous other species, 

 including members of the genera Scaptomyza and Chymomyza, have 

 been found to thrive on it. 



V. PARASITES AND ENEMIES OF DROSOPHILA. 



Protozoan parasites: Chatton and his coworkers (1908, 1911, 1912) 

 have described flagellate parasites from the digestive tract and Mal- 

 pighian tubules of the European Drosophila confusa Staeger. These 

 are described as probably belonging to four distinct genera; but 

 Minchin (1912, Introduction to the Study of the Protozoa) interprets 

 them as different stages of the same parasite, which he places in the 

 genus Leptomonas. The effects produced on the hosts, and whether 

 or not other species of Drosophila have the same or similar parasit es 

 are points not yet known. 



Fungus parasites: Thaxter (1895, Mem. Amer. Acad. Arts and Sci., 12,. 

 300; 1914, Botan. Gaz., 58, 235; 1917, Proc. Amer. Acad. Arts and Sci., 

 52, 699) has described several fungi that are external parasites on 

 species of Drosophilinse. These fungi belong to the genera Muiaria 

 (Hyphomycetes) and Stigmatomyces (Laboulbeniales) . Each of these 

 genera is recorded both from Drosophila and from Leucophenga. The 

 effects on the hosts are apparently unknown. 



Nematodes and mites: Small mites are frequently to be found 

 crawling over living specimens of Drosophila. When numerous they 

 are apparently harmful, but I have not determined the manner in 

 which they affect the host. 



Soil-living nematodes often occur in enormous numbers in fruit 

 exposed on the ground, and Drosophila fed on such fruit sometimes 

 has tangled masses of worms on its legs, wings, and bristles. These 

 appear as opaque white masses. They are injurious in that they 

 impede the movements of the fly and make it sluggish. 



