208 



SYSTEMATIC ZOOLOGY 



Aphids (Fig. 205) belong here; they are for the most part not 

 more than six or seven millimeters long, some with two pairs 

 of wings, some without any, and many secrete a sweet, sticky 

 substance from the abdomen, called honeydew, upon which other 

 insects, such as bees, wasps, and ants, feed. 



There are many kinds of aphids : the woolly aphids, which 

 cause the alder blight, the beech tree blight, the woolly louse of 

 the apple tree, the cherry tree aphis, the hop aphis, the peach 



tree aphis, which causes the leaves to 

 curl up, though this is often due to 

 other causes as well, the elm gall and 

 the poplar leaf gall, and one of the most 

 important, Phylloxera, which has done 

 so much injury to the grape vines of 

 Southern France. The grape Phyl- 

 loxera (Fig. 206) attacks only certain 

 species of grapes. The larva hibernates 

 in the ground, and in the spring develops into a wingless female, 

 which deposits her eggs on the young roots of vines; the roots 

 then appear swollen and knotty, and eventually die. From these 

 eggs young are produced parthenogenetically, mostly wingless 

 like the parent; but eventually winged forms are developed, 

 which make their way above ground and spread to neigh- 

 boring vines. These deposit eggs, some small, some large, 



Fig. 207. Enckenopa, a tree 



hopper common on locust i 

 Lateral aspect and anterior 

 view; natural size, about thir- 

 teen millimeters long. (Drawn 

 from specimen by the author.) 



Fig. 208. Cicada. (After Guerin and Percheron, from Parker and Haswell's Text-book.) 



which develop parthenogenetically into males and females 

 respectivelv. Each pair of these sexual individuals gives rise 

 to a single egg, which develops into a wingless form like the 



This last-formed female may go 



original hibernating insect 



