102 INSECT PHYSIOLOGY 



others require carbohydrate, if they are to produce their full comple- 

 ment of eggs. But the most generally important food factor is protein : 

 flies such as Calliphora oxLucilia can be kept alive for long periods on 

 sugar and water alone, but the females must have at least one meal of 

 protein before eggs are laid. There are other factors, such as lecithin, 

 which may be essential for some insects; as indeed are vitamins. The 

 fecundity of Drosophila females is largely influenced by the quantity 

 and variety of yeast in the diet; and the Rhodnius female deprived of 

 its intestinal actinomyces fails to produce eggs (p. 70). Sometimes the 

 nutrition of the larva has an important influence; that is particularly 

 so in those mosquitoes which will produce eggs from reserves accu- 

 mulated in the larval fat body without feeding at all in the adult 

 stage. 



Some insects will produce a normal number of eggs without being 

 mated ; but in most the full development of eggs occurs only after 

 impregnation. Sometimes this is an effect merely on oviposition : the 

 eggs are formed but are not laid unless mating has occurred. On the 

 other hand, in many insects the development of eggs is deficient in 

 the absence of the male. In some insects, mating with a sterile male 

 (in which spermatophores or accessory gland secretion are produced) 

 is ineffective; and that has led to the suggestion that the moving 

 sperms themselves provide a tactile stimulus acting through the 

 nervous system. 



If the insect is inadequately nourished, particularly if it is deprived 

 of protein, the young oocytes develop in the follicles until they reach 

 the stage at which yolk should be deposited. Then they die and are 

 absorbed and a new oocyte moves down. This process of degenera- 

 tion results from the lack of secretion from the corpus allatum. We 

 saw (p. 88) that the corpus allatum ceases to secrete the juvenile hor- 

 mone at the final moult, so that metamorphosis can occur. But in the 

 adult insect the same hormone is again produced and is usually 

 necessary for the deposition of yolk. That has been shown in Rhod- 

 nius, in grasshoppers (where the juvenile hormone is needed also for 

 the secretory activity of the oviducts which form the ootheca), in 

 Bytiscus and other beetles, and in Diptera. It seems not to be neces- 

 sary in some Lepidoptera, such as the silkmoths Bombyx and Hya- 

 lophora which develop their eggs during the pupal stage; but in 



