4 FARMERS’ BULLETIN 722. 
both apple and pear are also attacked, the light-colored pimples 
occurring mostly around the calyx end of the fruit and resulting in 
no material injury. The injury 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. The mite has been recorded 
from foliage on the white beam tree, the European mountain ash,’ 
the wild service tree,’ the service berry,* and the common cotoneaster.® 
According to one entomologist the mites have been found on over 
250 varieties of apples, injury being severe on some well-known com- 
mercial sorts, as Ben Davis, King, Baldwin, Rhode Island Greening, 
and at the agricultural experiment station at Geneva, N. Y., the 
Williams 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, measur- 
ing on the average about one one-hundred-and-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 sete 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 larvee feed upon the cellular leaf substance, work- 
ing 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 
ina 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 
1 Sorbus aria Crantz. 2Sorbus aucuparia L. *% Sorbus torminalis Crantz. 4A melanchier 
vulgaris Moench. 5 Cotoneaster vulgaris Lindl. 
