foliage or the growing shoots, and these may be forms that devour tlfe 

 foliage directly or suck the juices from the tissues. There is no one 

 insecticide that kills all kinds of insects under all conditions, and it 

 therefore becomes necessary to consider the leading injurious species 

 in a somewhat systematic way, indicating under each heading just 

 M-hat materials should be nsed. 



PLANT LICE. 



Plant lice are small, usually green or brownish insects found on 

 the under sides of leaves or on growing shoots, that multiply rapidly 

 and nourish by sucking the plant juices. The mouth-parts consist of 

 a jointed beak covering three or 

 four very slender lancets, by 

 means of which the tissue is 

 punctured. An individual plant 

 louse is rarely more, and gen- 

 erally less, than one-eighth of 

 an inch in length, slender and 

 capable of taking only a small 

 amount of sap from the plant. 

 When the lice are few their in- 

 juries are unnoticed, but fre- 

 quently they are so abundant that 

 the drain becomes serious. Every 

 leaf may be burdened by dozens, 

 or even hundreds, and the insects 

 are not satisfied with taking just 

 enough to maintain life; they 

 pump continuously, and, when 

 full to repletion, eject the excess 

 through either the anal opening 

 or through two little honey tubes 

 near the end of the body. Where plant lice are numerous this honey 

 dew as the excreted juice is called, is sometimes so abundant as to coat 

 the pavements with a sticky mass. The leaves themselves become 

 --overed and it forms an excellent surface for a black soot-fungus, that 

 tends to choke the leaves, and so kill them. We have, therefore, not only 

 the direct drain upon the foliage, but also a secondary effect due to 

 clogging. Norway maples, among the shade trees, are the greatest 

 sufferers; the tulip and elms also are more or less troubled, while 



Tig. 1. 



Mouth structures of a plant louse : o, the beak ; 



6, the piercing lancets; c, antenna 



or feeler ; d, the foot. 



