228 MONTANA EXPERIMENT STATION. 



THE PEAR=LEAF BLISTER MITE. 



{Phytoptus pyri Scheuten.) 



Though probably of European origin the pear-leaf blister-mite 

 is now widely disseminated throughout the world, having been dis- 

 tributed by the agency of traffic in nursery stock. It is sparingly dis- 

 tributed in Montana, but where well established is a troublesome 

 pest. 



NATURE OF INJURY. 



As the leaf-buds of affected trees unfold in the spring there may 

 be seen red blister-like spots and blotches which in severe cases may 

 involve practically all the surface of the leaf. At first the galls are 

 more distinctly seen on the upper surface of tl^ leaves but later in the 

 season the spots turn brown, owing to the death of the tissues com- 

 prising the blisters, when the affected spots become more apparent 

 on the under side of the leaves. The blotches often take the shape 

 of elongated patches one on each side of the midrib. 



In each blister, on the under side of the leaf, may be seen one 

 or more minute holes that lead to the cavity of the blister and usu- 

 ally visible only under a lense or microscope. 



Within these blisters composed of abnormal plant tissues, the 

 mites live, feeding on the juices of the plant. Under the shelter of 

 these galls they are very well protected, not only from wind and rain 

 which might easily sweep them off, but also against insecticidal 

 treatment. The tissues on the inside of the galls also furnish better 

 facility for the mites to acquire nourishment than would the thicker 

 layers of cells on the surface. The freshly formed galls are thick and 

 succulent, but as they die and turn brown they shrivel and dr3\ 

 Badly affected trees lose their foliage long before the normal time 

 which must be an injury to the health of the tree. 



THE MITE. 



The mites that produce these galls are very minute, being 

 scarcely visible to the naked eye. Under a high power microscope, 

 the body is seen to be elongated in form, about four times as long 

 as wide, and has the appearance on the surface of being made up of 



