RODUC1 



:her winged or wingless; but, 9O far as is known, the 

 females that pair with the males are aluays windless. Th 

 females aft ;iing impregnated, produce the winter eggs ; thus 



mpletcd th t changes through \\huh th< 



In mat 1 t, the individuals of the agamic generation 



that immediately precedes the sexual one produce but few pseudova ; 



:dova the sexual individuals emerge, not as l.n 



but as fully developed individuals, ready to pair and reproduce ; in 

 . in the cases referred t. the sexual individuals have the mouth- 

 parts in a rudimentary state, and take no nourishment. In many 

 the impregnated female prodih .;. which is 



nearly as large as the insect herself; frequently th ; s egg is 

 laid, but remains throughout the winter in the dry skin of the dead 

 parent. 



unic Aphides may hibernate, and may coexist with the sexual 

 ration of the same speci 



in the above generali/ations it will be seen that a single 

 of plant-louse may present three distinct forms: first, a 

 ntary. agamic, wingless form, furnished with mouth-parts; 

 second, a migrating, agamic form, which is winged and furnished 

 with mouth-parts; third, a sexual form, of which the females 

 wingless, while the males may be either winged or wingless; in cer- 

 tain it least, the sexual forms are inouthK 



There is unfortunately a generalization in most of the text-books 

 on entomology that is incorrect. It is that the winged generation is 

 produced only on the approach of cold weather, and that this gen- 

 eration is the sexual one. 



Plant-li [ten very destructive to vegetation ; they ap; 



however, to be more liable to attack unhealthy plants than those 

 that are in good condition. The best method of destroying tl. 



by spraying with a strong solution of soap, or with 1, 

 emulsion. (See Chapter XIV.) As plant-lice draw their nourish- 

 ment from below the surface of tin- plants they infest, they are not 

 injured by the application of poisons to the plat 



The Aphididae Comprises tour sub-families; the following table 

 for separating these sub-families is published by I )r. Thomas, in the 



ortofth Entomologist of Illinois. Itisnt 



the names applied to the veins of the w 



them are used in this table. The principal vein of the front wing, 

 that which extends from the base to near the tip of the wing, (1 



