HEMIPTERA 



251 



Pro^horojc 



M£so hhorax 



rvvncf 



(caUi 



described above (p. 241), but while most feed on plant juices, 

 some, such as the bed-bugs [Cimex, Fig. 182) suck blood. Many 

 of the herbivorous forms are of great economic importance both 

 because of the direct damage which they do and because of the 

 virus diseases which they carry. 

 Many species, such as the bed- 

 bugs, are wingless, while others, 

 such as the Aphididse or greenflies 

 (Fig. 183) have wingless forms. 

 This last family is also of interest 

 for its peculiar and complicated 

 life-cycles, which are generally of 

 the following pattern. An egg 

 which has survived the winter 

 hatches in spring to form a wing- 

 less female. She feeds, and rapidly 

 produces about forty young ones ; 

 these are all wingless females, 

 have been formed by parthenogenesis, that is, from eggs 

 which have not been fertilised, and are hatched within the 

 body of their mother, so that they are said to be produced 

 viviparously. Each in its turn reproduces in the same way, and 

 similar generations occur throughout the summer. There is thus 



Fig. 182. — The Bed Bug, Acanthia 

 [=^ Cimex) lectidaria x c. 12. — 

 From Murray, after Butler. 



Fig. 183. — The Turnip-leaf Plantlouse {Aphis rapcB). — After Curtis. 

 2 and 4 winged and wingless parthenogenetic females ; i and 3 natural size of the same. 



very rapid multiplication but Httle spread of the animal. Even- 

 tually, in late summer, a winged brood appears, and some of the 

 bugs in this are males. The winged forms fly to neighbouring 

 plants and copulate. Each female then lays one fertihsed egg, 

 which may survive the winter and start a new cycle in the spring. 

 There are variations on this theme, mostly in the direction of 

 greater complexity. Dor alls {= Aphis) rumicis lays the fertilised 



