THE INSECT WORLD. 



137 



the door closed, and bisulphide evaporated from a vessel hung up 

 just below the top of the box. As the vapors descend, they will 

 kill the insects infesting the plants, which may then be sent out 

 free from all insect troubles. One dram of liquid per cubic foot 

 of space will be about the right quantity not likely to hurt vege- 

 tation, while killing all lice by the time the liquid has entirely 

 evaporated. 



The "jumping plant-lice" are so called from their habit of 

 leaping readily, though, as a matter of fact, their resemblance is 

 rather to the tree-hoppers, and most of all they recall a miniature 



Fig. 99. 



The pear-psylla — a, pupa from under side, showing the thread-lilie piercing lancets; 

 to the right, a winged adult and stalked egg. 



cicada. They all belong to the family Psy/lidcs, some species of 

 which are exceedingly troublesome, — e.g., the "pear-psylla," 

 Psylla pyricola. This infests pear-trees in the more northern 

 parts of the country, extending south to Maryland, though 

 south of New York State it occurs in isolated patches only. It 

 does its injury, first, by sucking the juices of the plant and so 

 weakening it ; second, it exudes honey-dew in such quantity as 

 actually to close the pores of the leaves and young bark, over 

 which a fungus forms and checks growth. It commonly attacks 

 the stalk of the fruit, or the twig just where it is fastened, and 

 the result is nearly always a cessation of growth in the pear itself 

 The species has several broods during the season, but winters as 



