MICRO-ORGANISMS 245 



deficiency lies at least partly in the low concentration of vitamin 

 B which appears to be present largely in the wheat kernel. 



Chapman (1924), using another flour insect, the beetle Tribolium 

 confusum, came to the conclusion that the wheat embryo itself 

 is more satisfactory for growth and transformation than other 

 food substance. Vitamin B from the wheat embryo did not 

 appear to be able to supplement deficient diets, and it would seem 

 that some substance other than this vitamin may be involved. 



The nutritional requirements of the larvae of the Sheep Blow-fly 

 (Lucilia sericata) have attracted a good deal of attention during 

 the last few years. This work has been in connection with the 

 importance of this species as an animal pest. The old idea that 

 bacteria play an essential role in the process of digestion is not 

 borne out. The extensive researches of Hobson, in a series of 

 ten papers pubhshed between 1931 and 1935, and of others, have 

 been reviewed by Evans (1936). It appears that the chief functions 

 played by bacteria are to supply a growth-promoting substance 

 and to liquefy the food. Other accessory growth factors necessary 

 for normal growth and development are cholesterol, vitamin B, 

 together with certain substances analogous to members of the 

 vitamin B complex. 



Without further discussion of this subject it will be evident that 

 substances of the nature of vitamins are essential for the growth 

 of certain insects, but it should not be too readily assumed that 

 they are necessarily identical with those required by the higher 

 animals. For certain other insects, evidence that vitamins are 

 essential factors in the nutritional process is far from conclusive. 



Symbiotic Micro-organisms. The literature dealing with the 

 association of micro-organisms with insects has assumed extensive 

 proportions, but restrictions of space will only permit of limited 

 reference to the subject. In a number of cases, of which the 

 malaria parasite and Nosema disease are familiar examples, such 

 organisms are parasitic in behaviour. In other instances their 

 relationship is of the nature of inquilines, or they are neutral, 

 in that they neither confer obvious benefit to their hosts nor 

 occasion deleterious consequences to the latter ; the intestinal 

 bacterial flora prevalent in many insects probably comes under 



