616 The American Naturalist. [July, 
ENTOMOLOGY ` 
The Pear Leaf Blister.—Mr. M. V. Slingerland has recently 
rendered an important service to economic entomology by showing 
that the injuries of Phytoptus pyri, the mite which causes the pear leaf 
blister can be controlled by spraying the trees in winter with kerosene 
emulsion. In a recent bulletin? he presents the most satisfactory 
account of this pest that has yet been published, recording the experi- 
ments which have led to the discovery of the remedy. The disease is 
said to appear on the leaves early in spring “in the form of red blister- 
like spots an eigth of an inch or more in diameter. During this red 
stage of the disease, the spots are more conspicuous on the upper sur- 
face of the leaves. About June 1, the spots gradually change to a 
green color hardly distinguishable from the unaffected portions of the 
leaf; this change takes place on the lower side of the leaf first, and 
the spots may thus be r 
above and green below. In 
this green stage, which seems 
to have been overlooked, the 
badly diseased leaves present sz 
a slightly thicker corky ap- 
pearance; otherwise the dis- 
ease is not readily apparent Fig. 1.—Phytoptus pyri. Magnified. 
especially where not severe. This green stage lasts about a week or 
ten days; and about June 15, the spots may be found changing toa 
dark brown color beginning on the lower side of the leaf. The tissue 
of the diseased parts or spots then presents a dead, dry, brown or black, 
corky appearance. The spots are also more conspicuous on the lower 
side and remain unchanged until the leaves fall in the autumn. They 
occur either singly scattered over the surface of the leaves or often 
coalesce forming large blotches which sometimes involve a large por- 
tion of the leaf." 
In describing the life history of the Phytoptus mite Mr. Slingerland 
says: “The exceedingly minute oval grayish eggs are laid by the 
females in the spring within the galls that they have formed, and here 
! Edited by Clarence M. Weed, New Hampshire College, Durham, N. H. 
*Cornell University Agr. Exp. Station Bull. 61, pp. 317-328 
