THE B VITAMIN REQUIREMENTS OF ANIMALS AND PLANTS 315 



is able to increase excretion of the pigment. Finally, raw egg white or 

 avidin concentrate, when added to the diet, causes death of the larvae in 

 about four weeks, while pretreatment of the concentrate or egg white by 

 means which destroy avidin permits normal larval growth. When larvae 

 are changed from egg white diets to diets containing various levels of 

 biotin, the growth is renewed at rates in accordance with the biotin 

 present. 37 The nicety of these responses is illustrated in Figures 3 and 4. 

 Thus in many ways at least the rice moth larva resembles the vertebrates 

 in its metabolism of thiamine, pyridoxine, and biotin. 171-80 The extension 

 of these studies of the Coonoor Nutrition Research Laboratories will be 

 anticipated with great interest. 



The insects mentioned above represent a number of the more important 

 orders of the class Insecta. Many others have not been investigated. The 

 order Thysanura (silverfish), because of its primitive nature, ubiquitous 

 distribution, and economic importance, certainly challenges the investi- 

 gator. Indeed the entire class Arachnida, for many reasons important, 

 remains virtually unstudied with regard to its B vitamin requirements. 

 Perhaps the single exception to this statement is the work of de Meillon 

 and co-workers on the blood-sucking tick, Ornithodorus moubata. These 

 workers found that this tick (as well as the common bedbug, Cimex 

 lactularis) , when feeding on thiamine-deficient rats, requires an average 

 of 79.7 days to develop as compared with 41.1 days on normal rats. 38 

 They further found that definite toxic effects were observable in blood- 

 sucking arthropods that fed on rabbits injected with y-hexachlorocyclo- 

 hexane, suggesting an interference with inositol metabolism. 39 It is truly 

 remarkable that the vast effort put into the study of tick-borne diseases 

 has not produced similar more extended studies of the nutrition of the 

 insect vectors. Indeed future studies of insect-borne disease may well 

 start with a study of the nutrition of the host, as an approach to insecti- 

 cides that might be organized on logical lines of reasoning, based upon 

 present knowledge of the inhibition of vitamin metabolism. 



In summary, our knowledge of invertebrate nutrition is practically 

 nonexistent, and, at best, is based upon presumptive evidence, in the 

 phyla below Arthropoda. This scant evidence, however, suggests that 

 these lower phyla have extensive B vitamin requirements. 40 Among the 

 Arthropoda, information approaching adequacy exists only in the class 

 Insecta, where the available data indicate that B vitamin requirements 

 are as extensive as those of the vertebrates. The problems involved in 

 invertebrate nutrition are such as to offer great inducement to the in- 

 vestigator, and are further significant for physiological, medical, economic, 

 and taxonomic reasons. 



