18 



also -similar cultures of the moth Galleria melonella . 

 The work of Glaser (192 1 +) showed that the growing larvae 

 of flies were dependent on certain accessory growth factors 

 which may "be obtained from "bacteria and yeasts, hut that 

 microorganisms and their^ activities are not absolutely 

 essential to the normal growth, development and longevity 

 of flies. Later (1938) he developed a method whereby 

 house flies could be raised in sterile culture, free from 

 microorganisms. Baumberger (1919) reported that the larvae 

 of the fly Desmometopam - nigrum Zett. are probably dependent 

 on microorganisms and that the larvae of the house fly 

 very probably feed on microorganisms. Trypetidae larvae 

 can develop only when microorganisms are present, accord- 

 ing to Stammer (1929). 



Bacteria and the physiology of insect digestion . Con- 

 siderable evidence has been advanced that bacteria may 

 play a greater role in the nutrition of insects than merely 

 serving as food. Bacteria are capable of producing pro- 

 teolytic, lipolytic, saccharolytic, amylitic and other 

 enzymes which no doubt exert considerable influence on the 

 digestive processes of the insect harboring them. 



The best known examples of such a relationship are 

 those concerned with the intestinal flagellates which take 

 an active part in the digestion of cellulose in the gut 

 of the termite and in the wood-feeding roach Cryptocercus . 

 However, we shall limit ourselves here to a brief discus- 

 sion of the bacteria which maintain similar relationships. 



Petri (1905) was one of the earliest to assign to the 

 bacteria a definite digestive role. The bacteria constant- 

 ly present in the ceca of the olive fruit fly ( Dacus oleae ) 

 were found to produce lipase. It was suggested that the 

 activity of the bacteria in the digestion of fats must be 

 very important for the larva which feeds on the olive, «a 

 fruit rich in fats. In a later paper (19IO), he asserts 

 that partial digestion of the oil might be possible without 

 the aid of bacteria, since many larvae living on seeds rich 

 in oil do not possess intestinal bacteria. Bogdanow (1906) 

 believed that the formation of ammonia during larval de- 

 velopment of Calliphora vomitoria is not a characteristic 

 of protein digestion by the larvae but probably a result 

 of bacterial activity. Weinland (1907), on the other hand, 

 insisted that the ammonia is the result of larval metabol- 

 ism. Wollman (1911, 1921) indicates that Weinland was 

 mistaken as no ammonia is produced by sterile larvae and 

 its production, therefore, must be due to microorganisms. 



