THE PEAR LEAP-WORM. 



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, h), 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 larvae 

 to consume such a leaf en- 

 tirely. When two or more 

 larvae are feeding simultan- 

 eously on the same leaf they 

 frequently cut the midrib in 

 two at about the middle of 

 the leaf, and the portion thus 

 cut o£f falls to the ground. 

 Severe infestations cause the 

 defoliation of branches (PL II, 

 fig. 2). The larvse 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 Fig. l— The pear leaf-worm {Oymmnychus californicus): 



observed in 1914 that were <^'l^^^i^'^'^'^'l^^f^'^^^\^^o^^i^^y^^^^z%^^s\xu-,b, 



enlarged section of leaf showing egg m tissue and manner 

 from one-third to nearly one- of feeding of young larva; c.full grown larva. o, Slightly 

 haK defoliated. Such infes- enlarged; 6, c, much enlarged. (Original.) 



tations, however, are not common. The lower parts of large trees are 

 the more heavily infested. 



The eggs arc usually laid in leaves that arc not yet unrolled, and 

 those which fail to hatch often deform or curtail tho growth of the leaf, 

 possibly by cutting off its food supply between the point where the 

 egg was d(^posited and tlie edge of tho loaf, making the latter one- 

 sided (PI. I, fig. .'■>). "WTicn the eggs hatch normally this malforma- 

 tion does not occur. Tho puncture of tho ovipositor frequently causes 

 a discoloration of tho adjacent tissues and sometimes wilts young, 

 Umder leaves. 



llio larva apparently will eat tho foliage of all cultivated varieties 

 of ])(;ur. 



