A NUTRITIONAL STUDY OF INSECTS 43 



3, The larvae are dependent on the nucleoprotein of yeast 

 for special substances necessary in their growth. 



4. The function of yeast in the ecology of the insect is to con- 

 centrate at the surface of the medium and to synthesize into 

 nucleoprotein, the urates, ammonia, or amino-acids of the sub- 

 stratum. 



2. Experiments with a sarcophagous insect 



A pair of adult Acalyptrate rnuscid flies of the species Desmo- 

 metopa m-nigrum Zett. (determination by ]\Ir. C. W. Johnson) 

 were received through the courtesy of Dr. W. ]\I. J\lann. They 

 had emerged from some poorly dried snail shells, collected in the 

 Fiji Islands, on the decaying flesh of which the larvae had fed. 

 The adults were placed on banana and yeast agar, where the 

 female deposited about forty eggs, most of which died owing to 

 a thick mat of a black mucor that grew over the surface of the 

 medium. The six larvae that emerged fed readily on the rich 

 yeast food, and in about tw^enty-two days reached a size of 12 to 

 15 mm. in length. The black fungous mat was not destroyed 

 and did not seem to injure the larvae. The six pupae formed 

 were normal, and six adults emerged after three to five days and 

 oviposited on the medium. 



The usual manner of interpreting the normal feeding habits of 

 this species would be to state that the larvae fed on decaying ani- 

 mal tissue. This, however, is oi:)en to doubt in view of the above 

 experiments, and we must now^ consider the probability that all 

 decaying or fermenting substrata are merely the media on which 

 the fungus and bacterial food of the insect is growing. 



3. Experiments uiith a coprophagoiis insect 



An investigation of the food of the housefly (Musca domestica) 

 also gi\'es support to this theory. The insects were obtained in 

 winter by placing bran mash in the greenhouse. The mash was 

 prepared by boiling "Educator" bran with an equal volume of 

 water with constant stirring for twenty minutes. It was placed 

 in a large porcelain dish in the hothouse, where it soon became 



