16 



upon insect physiology and nutrition. Despite this 

 obvious possibility, very little investigation has -been 

 made on the actual function of bacteria and other micro- 

 organisms in such processes. 



Bacteria as food . Besides the possibility of being 

 related to the food habits of an insect and aiding in its 

 digestive functions, bacteria may serve as food. 



Mitchell (1907) ™as one of the first to express the 

 belief that the "wriggler" of Stegomyia fasciata is pre- 

 eminently a bacteria-feeder, because the larvae develop 

 rapidly in water contaminated with sewage. In later years 

 her belief was supported by the work of Bacot (1916), 

 Atkin and Bacot (1917), Barber (I928), Rozeboom (1935) and 

 others. In Bacot' s report the suggestion that the bacteria 

 served as food for the mosquito larvae was based on the 

 clearing action the latter displayed in water, originally 

 turbid from, its enormous bacterial content, in conjunction 

 with the fact that the gut contents of larvae taken from 

 this water showed relatively few bacteria. He attributed 

 the scarcity of bacteria to their being rapidly digestedo 

 Barber (1927, 1928) found that algae alone, bacteria 

 alone, or infusoria alone may serve as a sufficient source 

 of food for Anopheles larvae but that a combination of 

 bacteria with infusoria or with algae appeared to afford 

 the best conditions for the growth of Culex quinquefasciatuE 

 and of Aedes aegypti . 



From the intestinal examination of over 600 mosquito 

 larvae, Hinman (1930) concluded that the larvae ingest 

 any material small enough to be taken in through the mouth. 

 A considerable amount of this material appears to pass un- 

 changed through the alimentary canal. Whereas larvae 

 failed to develop in sterile, synthetic media or in auto- 

 claved water taken from normal breeding places, the addi- 

 tion of certain types of bacteria to such water made it a 

 suitable medium for complete larval development. Hinman 

 (1933) later demonstrated the existence of a factor in 

 bacteria which stimulated the growth of mosquito larvae, 

 but he was unable to extract this vitamin-like substance 

 from the bacteria with any regularity. Filtrates from 

 these cultures failed to stimulate development. In 1935; 

 Rozeboom studied the problem and concluded .that bacteria, 

 to a certain extent, can be utilized as food by mosquito 

 larvae though all kinds of bacteria are not equally suita- 

 ble as food 'for mosquito larvae. "Environmental m bacteria, " 

 associated with the natural breeding places of mosquitoes, 



