18 



J. PERCY BAUMBERGER 



that these micro5rganisms are not as valuable to the insect as 

 yeast cells. A few larvae were reared on vinegar-plant agar, 

 pupating on the sixth day. On manure agar growth was slower 

 and pupation took place on the fifteenth day. On lactic acid ba- 

 cillus and on Rhizopus nigricans agar no growth took place, but 

 the larvae died in three to five days. On plain agar infected with 

 a semianaerobic bacterium a few larvae pupated after twenty-six 

 days. Therefore yeasts are a more complete food for Drosophila 

 larvae then other bacteria or fungi. 



I have already shown that fruit (banana) is of some food value 

 for Drosophila larvae, as it will keep the insects alive for periods 



S. " Sea //t g/ /arra. 



'I '1 '\ ■^ 'I •! 'I »l 



tf. t 1^ i|» !|ii 111 i|j Hi i;. tjs 



Fig. 4 Larval growth on various media. 1, 24 per cent yeast; 2, maximum 

 3 to 12 per cent yeast; 3, minimum 3 to 12 per cent yeast; 4, vinegar plant; 5, 

 mushroom; 6, yeast nucleoprotein, sugars, and salts; 7, 2 per cent yeast; 8, hot 

 aqueous extract of banana; 9, 1 per cent yeast; 10, cold aqueous extract of banana. 



of twenty-eight to forty-four days and permit them to increase in 

 size to a limited extent. 



The activity of the larvae and analysis of the banana indicate 

 that the insect is abundantly supphed with carbohydrates (20 

 per cent sugar in ripe fruit). The protein content, on the other 

 hand, is relatively low (1 per cent) and is probably deficient. 



The long life of the larvae on sterile banana with the accom- 

 panying slow increase in size, indicates that all the food elements 

 required for maintenance and repair of tissues are present, but the 

 protein content is either too small or lacking or deficient in some 

 amino-acid necessary for growth. There is also the possibility 



