THE PEAR LEAF-WORM. 3 
worm may naturally feed upon the thorn apple, and if a native of the 
Pacific coast there probably exists another host to which it is adapted, 
and its habit of feeding upon pear may be an acquired one. This is 
not impossible, as various species of Crataegus and of Sorbus occur 
throughout the known range of the species. 
‘CHARACTER AND EXTENT OF INJURY. 
The injury caused by the pear leaf-worm (fig. 1) is confined among 
economic plants to the foliage of the pear and is due chiefly to the 
larva. While it consists primarily in the eating out of circular or 
semicircular holes in the leaf (fig. 1, a, b), often whole leaves are 
eaten down to the petiole. During its period of life a single larva 
eats about one-fourth of an 
average-sized pear leaf, so 
that it requires several larvee 
to consume such a leaf en- 
tirely. When two or more 
larvee are feeding simultan- 
eously on the same leaf they 
frequently cut the midrib in })/\_ 4A//"Mya” , 
two at about the middle of [i |i \ji) om 
the leaf, and the portion thus 4 \\jli4}/(ne7 
cut off falls to the ground. 
Severe infestations cause the 
defoliation of branches (Pl. II, 
fig.2). The larve are not ad- 
dicted to roaming and com- 
monly do not leave their 
original leaf as long as any 
edible part of it remains. In 
Washington many trees were Fic. 1.—The pear leaf-worm (Gymnonychus californicus): 
observed in 1914 that were @ Leaf showing character of injury and egg in situ; b, 
: enlarged section of leaf showing egg in tissue and manner 
from one-third to nearly one- of feeding of young larva; c, fullgrownlarva. a, Slightly 
half defoliated. Such infes- enlarged; b,c, much enlarged. (Original.) 
tations, however, are not common. The lower parts of large trees are 
the more heavily infested. 
The eggs are usually laid in leaves that are not yet unrolled, and 
those which fail to hatch often deform or curtail the growth of the leaf, 
possibly by cutting off its food supply between the point where the 
ege was deposited and the edge of the leaf, making the latter one- 
sided (PI. I, fig. 3). When the eggs hatch normally this malforma- 
tion does not occur. The puncture of the ovipositor frequently causes 
a discoloration of the adjacent tissues and sometimes wilts young, 
tender leaves. 
The larva apparently will eat the foliage of all cultivated varieties 
of pear. 
