The Biology of Ageing in Insects 



253 



and maturation. Indeed, an early paper by McCay and Crowell 

 (1934) reported that reduction in the protein content of the diet 

 fed to trout doubled their longevity. 



In insects too, there appears to be an optimal dietary level 

 of protein for growth and development and indirectly for 

 lifespan. Thus in three species of cockroaches (all of which are 

 not fully grown or mature at the onset of the final adult 

 stage), Haydak (1953) reported specific optimum dietary 

 protein requirements both for development and survival of 



Table II 



Effect of diet on the development and longevity of three 

 species of cockroaches (after haydak, 1953) 



the nymphal instars as well as for longevity of the adult. 

 Table II, prepared from Haydak's data, shows that for the 

 American cockroach the optimum protein for shortest nymphal 

 development and associated lowest nymphal mortality was a 

 broad range of 49-79 per cent; for either the Oriental or 

 German cockroach, this was a much lower 22-24 per cent. 

 For maximum adult longevity, on the other hand, the 

 optimum protein content of the diet was 22-24 per cent for 

 the adult diet of the American cockroach and 11 per cent for 

 both the Oriental and German cockroaches. Haydak con- 

 cluded from his data that for adults the heaviest protein 



