PLANT-LICE. 239 



found on mangolds (Ormerod) and on docks, from which they 

 take their specific name. 



The attack of this " louse " can easily be checked, if taken in 

 time, hy picking off the infested tops and putting them carefully 

 into a pail of lime, so as to kiU them before they spread low 

 down. Many plant-lice, like the above, have two food-plants. 



The Hap Louse {Phorodon humuli). 



If we examine a hop-plant early in the spring we shall notice 

 every here and there a large, fat, green, wingless aphis, the 

 mother or queen aphis. This early spring form has either come 

 out of the ground, where she has hibernated during the winter, 

 or from an egg which was deposited in the autumn. The spring 

 female is known as a viviparous female. She commences to 

 deposit living young upon the hop-leaves : these are the so-caUed 

 " lice," which have been produced asexually. Each louse, again, 

 has the power of producing living young asexuaUy, and this goes 

 on for several generations. Many lice then enter the pupal 

 state, bud-like outgrowths appearing at the sides of the thorax. 

 Another form of female that is still viviparous may now be pro- 

 duced from these pupsB — namely, a winged female, which flies 

 ofif to another hop-plant and there produces more living young : 

 this is the second or winged viviparous female. At the end of 

 the year the lice mostly turn into pupae, and from these are de- 

 veloped a third form of female, which is also winged — the ovip- 

 arous female ; and at the same time winged males are produced. 

 These autumn males and females copulate, and the female when 

 fertilised flies off from the hop to the damson and other prunes, 

 and there lays her eggs. A few apterous viviparous females 

 also go into the ground at the roots of the hop. Those that 

 fly to the prunes lay their ova upon the boughs : these 

 hatch into the Hop Aphis in the spring, and about the 

 middle of May develop wings, the winged females migrat- 

 ing back to the hops to deposit the lice. The form on the 



