THE LEAF BLISTER MITE. 



CHARACTER OF IXJURY AND DESTRUCTIVEXESS. 



The mites pass the Avinter 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 progeu}- feed upon the 

 tender cells of the leaf substance. Their activities within the leaf 

 tissues very quickly result in the flevelopment 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 usualh" with a reddish tinge 

 on the pear. The spots soon 

 increase in size, the largest be- 

 coming as much as one-eighth of 

 an inch in diameter. On pear 

 leaves the spots, as a- rule, be- 

 come red, often brilliantly col- 

 ored as they grow, whereas on 

 apple this reddish coloring is ab- 

 sent or faint. 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 

 thickness, and some may become somewhat shrunken. Figure 2 illus- 

 trates a gall on jjear leaf as seen in cross-section, the normal structure 

 being shown at n.; o is the opening to the interior of the gall and e 

 designates eggs of the mite. A cross-section of one of the dried-up 

 Sfalls is shown in figure 3. 



Fig. 2. — Leaf gall, in cross-section, of leaf 

 blister mite : o. Opening of gall ; e, eggs 

 of mite ; n, normal structure of leaf. 

 (After Sorauer. ) 



Pig. 3. — Section of leaf, showing structure of gall of blister mite in autumn : (j, Gall ; o, 

 opening of fiall. lAftor ("omstork. ) 



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. 

 AAHien numerous, however, the spots Avill 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 ma}'" 

 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 

 both apple and pear are also attacked, the light-colored pimples 



