THE LEAF BLISTER MITE OF PEAR AND APPLE, 3 
CHARACTER OF INJURY AND DESTRUCTIVENESS. 
The mites pass the winter on the trees, under the bud scales, and 
attack the leaves as soon as these begin to push out in the spring. 
They bore small holes from the underside to the interior of the leaf, 
where they deposit their eggs, and with their progeny feed upon the 
tender cells of the leaf substance. Their activities within the leaf 
tissues very quickly result in the development of galls or swellings. 
These are at first small, pimple-like eruptions, especially evident on 
the upper surface of young leaves, whitish in color on the apple, 
but usually with a reddish tinge 
on the pear. The spots soon in- 
crease in size, the largest becom- 
ing as much as one-eighth of an » Toee re : 
inch in diameter. On pear leaves i ays we OTP ZG au 
the spots, as a rule, become red, “= 
often brilliantly colored as they ic. 2.—Pear leaf gall, in cross section, of 
grow, whereas on apple this red- pe eee) Gat ORENIDE, OF cael. 
a L E 3 e, eggs of mite; n, normal structure of 
dish coloring is absent or faint. leaf. (After Sorauer.) 
On the underside of the leaf the 
galls are whitish and blisterlike, not differing much from the general 
color of the leaf surface. Later they turn brownish or black, due 
to the death of the injured leaf cells, lose much of their checks 
and some may become somewhat shrunken. Fi igure 2 illustrates a 
gall on pear leaf as scen in cross section, the normal structure being 
shown at 7, 0 is the opening to the interior of the gall and e desig- 
nates eggs of the mite. A cross section of one of the dried-up galls 
is shown in figure 3. 
oe \ ae a 
hd 
ae as 
Tic. 5.—Section of pear leaf, showing structure of gall of blister mite in autumn; g, Gall; 
0, opening of gall. (After Comstock.) 
On pear, the galls occur more along each side of the midrib of the 
leaf and on apple at the base of and along the margins of the leaf. 
When numerous, however, the spots will merge together, forming 
large patches or bands of variable size, often involving most of the 
leaf. When thus abundant the leaves may become more or less rup- 
tured and wrinkled, and in the case of the apple the margins may 
curl up, showing the underside. Leaves badly infested are likely 
to fall prematurely, resulting also in the dropping of the fruit from 
clusters with worst injured foliage. The fruit and fruit-stems of 
