: 
Crculah No. 154. 
United States Department of Agriculture, 
BUREAU OF ENTOMOLOGY. 
L. O. HOWARD, Entomologist and Chief of Bureau. 
THE LEAF BLISTER Mill.. 
{Briophyet pyri Pngenstecher > 
i:.\ a. I. iii \in i \m i . 
In Charge of Deciduous Fruit Insect Investigations. 
INTHODU" [TON. 
Leaf blister mites are among the smallest <>f animal forms which 
attack horticultural crops. These minute creatures, only one one- 
hundred-and-fiftieth of an inch in length, are invisible to the un- 
aided eye, and m> seen under a good hand lens appear a- the merest 
-peck. Although the mites themselves are probably unfamiliar to 
most ofchardists, their work is well known, to pear growers and 
apple growers, in the reddish or greenish pimples <>r blisterlike spots 
to Ik- noted in early spring on the young foliage of these plant-. 
Later these blisters become brown and dead, spotting and blotching 
the leaves, the injury resembling that due to leaf-spot fungi or from 
-I rays, with which injury, in fact, the work of this mite i- frequently 
confused. When the creatures are abundanl the foliage may be 
almost covered with the blisters or l.p.w n -pot-, and the usefulness of 
the leave- to the tree i- thus greatly impaired. Foliage severely 
injured will fall prematurely, retarding the development of the fruit 
and in extreme cases much id' the crop will fall to the ground. I S 
fig. 1.) 
The leaf blister mite i- not an insect, hut belongs to that class of 
animal- containing the spiders, scorpions, daddylonglegs, etc. and 
to the order Acarina, represented by such well-known form- a- the 
scah mite of sheep, the cattle tick, and the red spider. It- family, 
the Eriophyidae (Phytoptidse), contain- numerous species, all of 
which are plant feeders, attacking principally the hud- and lea 
Several members of the family are of much economic importance. 
ntie Landois infests vinifera varieties of grapes in por- 
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