INSECTS INJURIOUS TO THE APPLE AND PEAR 637 



The mites are not true insects, as they belong to the same class 

 as the spiders, scorpions, and ticks. One of the more common 

 larger mites is the red spider of greenhouses, which affects flower- 

 ing plants, vegetable crops, and fruits of all sorts. These little 

 blister-mites are of microscopic size, only 1/100 to 1/200 inch in 

 length, so that they can only be seen with a lens, and must be 

 examined with a compound microscope to distinguish the species. 

 One is shown much magnified in Fig. 493. They are elongate, 

 with two pairs of legs, and slender abdomens, composed of ">0 

 to 80 small rings, frequently marked with rows of small tubercles 

 and ornamented with a few hairs and bristles. 



Life History. The mites spend the winter in the buds, and 



FIG. 493. The pear leaf blister-mite (Eriophyes pyri Pgst.): highly magni- 

 fied. (After Parrott.) 



as warm weather approaches in the spring they become active 

 and move toward the base of the growing bud scales and feed 

 there. As the young leaves unfold the mites migrate to them. 

 They burrow through the surface of the leaf and feed upon the 

 succulent tissue within, setting up an irritation which soon results 

 in reddish spots on the surface. Within these mines the eggs 

 are laid, as many as 14 having been found in a single blister. 

 The young hatch in about a week and burrow around in all 

 directions, feeding on the tissues and juices. When full grown 

 they leave the gall through small openings in the under surface 

 and start new- colonies which produce similar galls. They con- 

 tinue to reproduce and migrate throughout the summer, and under 

 favorable conditions become numerous enough to completely 



