INSECT ENEMIES OF WESTERN FORESTS g7 



small, drab-colored moths. During heavy infestations practically all 

 of the leaves on the lower portions of the trees are attacked, but 

 infestation seldom extends above 50 feet. The damage results in a 

 premature shedding of the foliage. (3ther species of PhyUonorycter 

 include P. salicifoliella Chamb., which works in the under side of the 

 leaves of willow, poplar, and cottonwood; P. apicinigrella Braun, 

 which works in the under side of willow leaves; P. felinella Hein., 

 which w^orks in the under side of sycamore leaves in California ; P. 

 incanella Wlsm., Avhich works in both sides of alder leaves; and P. 

 arhutusella Braun, which works in the leaves of madroha. 



Cameraria agrifoliella Braun w^orks in the upper surface of leaves 

 of coast live oak. C. alnicoleUa Wlsm. works in the upper surface of 

 alder leaves. C. umbellulariae Wlsm. makes blister blotches on leaves 

 of California laurel. 



The aspen leaf miner Phyllocnistis populiella Chamb. (fig. 43) 

 leaves a labyrinthian trail of frass as characteristic of its work in the 

 under side of aspen and poplar leaves. 



Common leaf miners in live oak include Bucculatrix albertielld 

 Busck and Abehaea subsylvella Wlsm. 



SAWFLIES 



Sawflies form another important group of leaf-eating insects that 

 in many cases cause extensive defoliation and destruction of timber. 

 In the Northern States and in Canada, such species as the larch saw- 

 fly, the European spruce sawfly, and the jack pine sawfly have been 

 responsible for the death of as much as 85 percent of the stand over 

 thousands of acres. In the West the native sawflies occasionally de- 

 velop widespread outbreaks and may cause heavy defoliation over 

 limited areas, but the total timber destruction so far has not been 

 great. 



The sawflies (fig. 44) belong to the order of wasps (Hymenoptera) 

 but in appearance are usually more like flies than wasps. They have 

 thick, cylindrical bodies with four membranous wings, the hind pair 

 somewhat smaller than the forewings. The head, thorax, and base 

 of the abdomen are nearly equal in width. They range in size and 

 color from small grayish insects not over one-fourth inch in length 

 to large, showy species {Cimbex) over 1 inch long. They are called 

 sawflies because of a sawlike attachment which the female carries 

 at the tip of the abdomen and uses to slit open leaves or stems for 

 the reception of her eggs. Usually only one Qgg is deposited in each 

 slit, but as many as 14 or more punctures may be made in a single 

 pine needle. 



The larvae resemble hairless caterpillars except that most of them 

 have from six to eight pairs of abdominal legs, or larvapods, on the 

 abdominal segments, in addition to the usual three pairs of true legs 

 on the thoracic segments. Because of their resemblance to cater- 

 pillars the larvae are sometimes called "false caterpillars" ; and since 

 many are wormlike and often slimy, they are called "slugs" or 

 "worms." Most of them are typical external leaf chewers, but a few 

 are leaf miners and even gall makers. 



One of the most characteristic features distinguishing sawflies are 

 the cylindrical, papery, capsulelike cocoons wdiicli the larvae fre- 



