Effects of Castration in Insects 



403 



The social Hymenoptera, however, are not the only insects 

 which practice ahmentary castration. A very interesting case is 

 also seen in certain aphids of the genus Phylloxera, e.g., in the 

 Ph. caryae-fallax recently studied by Morgan ('09). The stem- 

 mother, or fundatrix of this insect makes and inhabits a hollow 

 gall on hickory leaves. She lavs numerous eggs which may give 

 rise to two kinds of offspring. The eggs first deposited produce 

 individuals that grow up to form the wingless sexuparae, (Fig. 3^), 



Fig. 3. Large wingless female of Phylloxera caryae-fallax; B and C, dwarf females of same, 

 drawn to same scale as A. (After T. H. Morgan.) 



while the eggs laid later give rise abruptly to very small females, 

 (Figs. 3/^ and C), which Morgan calls "supernumerary or dwarf 

 females." These he describes as follows: "In the larger galls 

 as many as 46 eggs may produce the large mdividuals, and then 

 the smaller series abruptly begins; while in the smallest galls 

 only one to three or four or more large individuals are produced 

 when the small series begins. There seems to be here not a prede- 

 termined number of large and dwarf females, but the conditions 



JOURNAL OF EXPERIMENTAL ZOOLOGY, VOL. 8, NO. 4. 



