PLANT LICE 



them aphids. A single plant louse is an aphis, or an aphid; 

 more than one are usually called aphides, or aphids. 



The distinguishing feature of the plant lice, or aphids, 

 as we shall by preference call them, is their manner ot feed- 

 ing. All the insects described in the preceding chapters 

 eat in the usual fashion of biting off pieces of their food, 

 chewing them, and swallowing the masticated bits. The 



Fig. 88. Group of green apple aphids feeding along a rib on 

 under surface of an apple leaf 



aphids are sucking insects; they feed on the juices of the 

 plants they inhabit. Instead ot jaws, they have a piercing 

 and sucking beak (Fig. 89), consisting ot an outer sheath 

 inclosing four slender, sharp-pointed bristles which can be 

 thrust deep into the tissues of a leaf or stem (Fig. 89 B). 

 Between the bristles ot the innermost pair (Fig. 90, Mx) 

 are two canals. Through one canal, the lower one (h), a 

 liquid secretion from glands of the head is injected into the 

 plant, perhaps breaking down its tissues; through the 

 other (a) the plant sap and probably some of the proto- 

 plasmic contents of the plant cells are drawn up into the 

 mouth. A sucking apparatus like that of the aphids is 

 possessed by all insects related to the aphids, comprising 

 the order Hemiptera, and will be more fully described 



h53] 



