A NUTRITIONAL STUDY OF INSECTS 3 



insects. Since they are largely phytophagous, insects are amply 

 supplied with carbohydrates, but have difficulty in obtaining 

 sufficient protein. The abundance of the former permits great 

 activity, while the dearth of the latter limits the growth of the 

 insect. This has led to a lengthening of the Hfe-cycle in those 

 species which must ingest large quantities of substrate in order 

 to get enough nourishment to complete their growth. However, 

 many insects that feed in decaying of fermenting vegetable matter 

 of low protein content have an unusually short period of growth. 

 The experiments and considerations which follow throw light on 

 the protein supply of such insects and account for their rapid 

 growth. 



These investigations were made at the Bussey Institution for 

 Research in Applied Biology, Harvard University, under Prof. 

 W. M. Wheeler. Valuable advice and assistance were received 

 from Profs. C. T. Brues, W. J. V. Osterhout, I. W. Bailey, and 

 Dr. R. W. Glaser. I am especially indebted to Doctor Wheeler 

 for helpful suggestions and encouragement. 



EXPERIMENTS 



1. Food of an insect (Drosophila) living in fermenting fruit 



A. Method and initial observations, a. Solid media for Droso- 

 phila. While rearing Drosophila it was found necessary to de- 

 termine the exact date of oviposition. As this is impossible in 

 the ordinary culture tube of fermenting banana, a solid trans- 

 parent medium was devised by myself and Dr. R. W. Glaser 

 (1917 a). 



This medium is made as follows : Mash six ripe bananas in 500 

 cc. of water, allow to infuse on ice overnight, strain through 

 cheese-cloth, and add 1^ grams powdered agar-agar to each 100 

 cc. of the filtrate. Heat in double boiler till agar is dissolved, 

 filter hot through absorbent cotton into test-tubes. Plug tubes, 

 sterilize in autoclave, and allow to cool in inclined position so as 

 to form solid slants of the medium. 



This medium is quite transparent, affords 15 to 20 sq. cm. area 

 for oviposition and 6 to 10 cc. of substratum for the larvae. The 



