140 



ECONOMIC ENTOMOLOGY 



wingless form, and =P= the viviparous agamic winged form, and 

 cf and 9 the sexual forms (Fig. 95). 



In general, plant-lice are soft-bodied and green, sometimes brown 

 or black. The winged forms have four delicate wings with a few simple 

 veins — the front pair much larger than the hind pair. The sucking 

 beak is 3-jointed; the legs and antennae are long and the eyes promi- 

 nent. In autumn the sexual females deposit eggs that hatch in the 

 spring into females which are often termed "stem-mothers." These 

 produce living females which in turn produce living females, and so on 

 for several generations. As each female produces several young, and 



these mature in a short time, reproduction is 

 very rapid. When autumn approaches and 

 food supply becomes scarce a brood of winged 

 males and wingless females is produced. 

 The females produce the winter eggs. Some- 

 times agamic females hibernate. 



There are many species of plant-lice, 

 some feeding on one variety of plant, but 

 many are capable of feeding on two or more 

 varieties. Some feed for a time on one host 

 plant, then migrate to another for the sum- 

 mer, finally returning to the first one in 

 autumn. Some produce abnormal growths 

 called galls, such as the grape phylloxera 

 gall, the cockscomb gall on the elm, the 

 Cottonwood gall, the poplar gall, etc. 



Most plant-lice excrete a sweet liquid called "honey-dew," which 

 is attractive to ants, bees, wasps and other insects. On account of 

 this honey-dew aphids are often attended by ants who guard them. 

 Forbes has shown that the little brown ant {Lasius niger) has domesti- 

 cated the Corn Root Aphis, which is cared for and controlled in all 

 stages of its development. (Consult Bull, no, 112, 276 and Farmers' 

 Bull. 804, U. S. Dept. Agr., and Bulletins by Parrott, Patch, Forbes, 

 Herrick and Matheson.) 



Fecundity. — Regarding the powers of reproduction of aphids Web- 

 ster and Phillips (Bull, no, U. S. Bur. of Entom.) cite the estimates of 

 Huxley and Buckton. The former estimated that the tenth genera- 

 lion alone of a single Rose Aphis, were there no deaths, would contain 



Fig. 95. — An apterous vivi- 

 parous female aphid. 



