120 ORDER n EMITTER A 



tough, usually black, i)(>lishe(l and resistant to the weather. 

 They are sometimes so abundant on the surface of apple 

 twigs as to give the latter a shiny appearance. The follow- 

 ing spring these eggs hatch into the stem-mothers. 



Control. — Control measures in general resolve themselves 

 into destruction of the over-wintering eggs, prompt appli- 

 cation of insecticides in early spring, and such measures as 

 are applicable through recognition of the alternate-host 

 habit. The hop-plant louse control depends on elimination 

 of the alternate host, wild plum. 



To the general and usual method of hibernation in the 

 egg stage there are exceptions. Thus the corn-root louse 

 is carried over the w^inter on roots in the ground by its 

 attendant ant. Through this dependence on the ant being 

 long-continued this species has evidently become independent 

 of the egg-depositing habit or produces eggs only at intervals. 



Outbreaks of plant lice are often very destructive and 

 and are more or less evanescent. The lice appear suddenly, 

 to all appearances, and often seem to disappear as quickly. 

 The aphids are victims to a multitude of predaceous enemies 

 and Hymenopterous parasites, are susceptible to weather 

 conditions, such as rains, low temperatures, etc. 



Migrations in spring are usually for short distances, rarely 

 over a mile or so, or until a suitable summer host is found. 

 Fall migrations, involving many more individuals, are much 

 more general and the insects more widely scattered, and are 

 carried along by wdnds and may be quite widely distributed 

 at that time. x\mong the important species are the corn- 

 root louse, hop-plant louse, cherry aphis, apple aphis, etc. 



An intimate relationship exists between the plant lice and 

 ants, this being sometimes carried so far as to make the 

 insects mutually dependent on each other. Such is the case 

 with the corn-root louse and its attendant ant, in which the 

 ant depends for its food upon the honey dew of the aphid 

 and the latter in turn depends upon the ant for its trans- 

 jjortation from one root to another. In this and other cases 

 plant lice are definitely ])rotected by the ants or carried over 

 from season to season in order that the ants may get the 



