Issued June 13, 1912. 

 CRCULAR No. 154. 



United States Department of Agriculture, 



BUREAU OF ENTOMOLOGY. 

 L. O. HOWARD, Entomologist and Chief of Bureau. 



THE LEAF BLISTER MITE. 



(Eriophins injri Pasensteclier. ) 



By A. L. QUAINTANCE, 



In Charge of Dcciditoiix Fruit Insect Inrest'igatlons. 

 INTRODUCTION. 



Leaf blister mites are among the smallest of animal forms Avhich 

 attack horticultural crops. These minute creatures, only one one- 

 hundrecl-and-fiftieth of an inch in length, are invisible to the un- 

 aided eye, and as seen under a good hand lens appear as the merest 

 speck. Although the mites themselves are probably unfamiliar to 

 most orchardists, their work is well known, to pear growers and 

 apple growers, in the reddish or greenish pimples or blisterlike spots 

 to be noted in early spring on the young foliage of these plants. 

 Later these blisters become brown and dead, spotting and blotching 

 the leaves, the injury resembling that due to leaf-spot fungi or from 

 sprays, with Avhich injury, in fact, the work of this mite is frequently 

 confused. When the creatures are abundant the foliage may be 

 almost covered with the blisters or brown spots, and the usefulness of 

 the leaves to the tree is thus greatly impaired. Foliage severely 

 injured will fall prematurely, retarding the development of the fruit 

 and in extreme cases much of the crop will fall to the ground. (See 



fig.l-) 



The leaf blister mite is not an in.sect. but belongs to that class of 

 animals containing the spiders, scorpions, daddylonglegs, etc., and 

 to the order Acarina. represented by such well-known forms as the 

 scab mite of sheep, the cattle tick, and the red spider. Its family, 

 the Eriophyidse (Phytoptida}), contains numerous species, all of 

 which are plant feeders, attacking principally the buds and leaves. 

 Several members of the family are of much economic importance. 

 Eriophyes vitis Landois infests vinifera varieties of grapes in por- 



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