New York Agricultural Experiment Station. 471 



INTKODUCTION. 



Plant lice are among the most important of the injurious in- 

 sects. They infest all kinds of fruits, vegetables and ornamental 

 plants. Although present every year, some seasons are more 

 favorable for their development than others. The past season 

 has been one of this kind, and various species of plant lice have 

 caused serious injury throughout the State, especially to orchard 

 and bush fruits. The large number of inquiries received at the 

 Station asking for information concerning the nature and habits 

 of these insects, together with the best-known methods of com- 

 bating them, indicate the wide-spread injury caused by the lice 

 and the need of information concerning them. 



Plant lice are also among the most difficult insects to study. 

 To work out all the details concerning the life history of any 

 one species would, under ordinary circumstances, require more 

 than a summer's work for a single individual. Observations on 

 the species referred to in this bulletin were not begun, systemat- 

 ically, until last spring. The work is, therefore, necessarily in- 

 complete; yet the existing circumstances are such that it seems 

 best to publish a portion, at least, of the results thus far obtained. 



PLANT LICE. 



Classification. 



Plant lice are true bugs. They belong to one of the larges: 

 and, from an economic standpoint, one of the most important 

 orders of insects, namely, the Hemiptera. The mouth parts of 

 insects of this group are modified into beak-like tubes, by means 

 of which they suck their food. They are thus also classed with 

 the suctorial feeders, as distinguished from those insects which 

 masticate their food. 



How Plant Lice Obtain Their Food. 



By carefully observing a plant louse when feeding, either from 

 directly in front or from the side, it will be observed that the 

 beak is extended so as to touch the surface of the leaf or is 



