INSECT TRANSFORMATION 



and capable of reproduction after less than two weeks' growth. 

 Thus successive generations of females are rapidly produced 

 during the spring by means of this curious virgin reproduction 

 (parthenogenesis}. Sooner or later a brood of young insects 

 arise which, after a couple of moults, show narrow wing 

 rudiments (Fig. 39 b) on the second and third thoracic seg- 

 ments ; these grow into winged aphids (Fig. 39 a), the two 

 wings of a side being alike delicate and gauzy in texture, the 

 forewings much larger than the hindwings, both with a charac- 



FIG. 39. VIRGIN FORMS OF GREEN APPLE APHID (Aphis pOWli). 



a, winged virgin female ; b, its nymph with wing-rudiments ; c, wingless virgin female ; 

 d, young, x 12. After Quaintance, Entom. Circ. 81, U.S. Dept. Agric. 



teristically reduced nervuration, carried when at rest with the 

 costa ventralwards. Such winged aphids can leave the plants 

 on which they were born and migrate to others where there 

 may be greater space and more abundant food. Thus through 

 spring and summer the virgin generations succeed each other, 

 some winged and some wingless, until with the approach of 

 autumn, males and females are born which, after pairing, 

 produce the hard-shelled winter eggs whence next spring's 

 stem-mothers will be hatched. In different kinds of aphids 



