4 THE LEAF BLISTER MITE. 



occurring mostly around the calyx end of the fruit and resulting in 

 no material injury. The injuiy to the fruit-stems is noticeable as 

 irregular thickenings, and when severe may cause some of the fruit 

 to fall, although loss from this source, even in worst infested orchards, 

 will not be great. 



FOOD PLANTS. 



Pear and apple are the more common food plants of the blister 

 mite, though other plants are attacked. Dr. Xalepa records this 

 species from foliage on the white beam tree {So7'hus aria Crantz), 

 the European mountain ash (So?^hus aucuparia L.), the wild service 

 tree (Sorhus torminalis Crantz), the service berry {Amelaiichier 

 culgaris Monch.), and the common cotoneaster {Cotoneaster vulgaris 

 Lindl.). 



According to Parrott the mites have been found on over 250 vari- 

 eties of apples, injury being severe on some well-known commercial 

 sorts, as Ben Davis, King, Baldwin. Ehode Island Greening, and at 

 the agricultural experiment station at Geneva, X. Y., the ^Villiams 

 Favorite was noted to be especially subject to attack, the trees having 

 been prematurely defoliated for two successive seasons. 



DESCRIPTION AND HABITS. 



The general appearance of the blister mite is shown in figure 4 

 in dorsal and ventral views. The mite is microscopic in size, measuring 

 on the average about one one-hundred-aiid-fiftieth inch in length, 

 whitish in color, a few individuals pinkish. The abdomen slopes 

 gradually toward the posterior end and is numerously ringed. There 

 are only two pairs of legs, and these and the body bear setae, which 

 from their character and location are of importance in the deter- 

 mination of species in this group, as are also the number and charac- 

 ter of rings on the abdomen. The young, except in size, bear a gen- 

 eral likeness to the adults, and the eggs, though proportionately 

 large as compared in size with the parent, are only 46 microns 

 through the greater diameter. These are whitish, translucent, with 

 rounded ends, and are deposited in the interior of the galls (see fig. 2). 

 The resulting larvfc feed upon the cellular leaf substance, working 

 out in various directions, though they are not especially active. 



The mites are to be found on the foliage from their appearance 

 in spring until fall, and several generations are evidently produced 

 in a season. Hibernation occurs under the bud scales, the mites often 

 congregating in colonies of 50 or more. They become active in the 

 spring often before the buds burst, congregating around the base of 

 bud scales, where they feed, many molting at this time. With the 

 bursting of the buds and the pushing out of the tender leaves, these 

 are attacked and the characteristic blisterlike spots soon develop. 



