78 MISC. PUBLICATION 273, U.S. DEPT. OF AGRICULTURE 



Key to Diagnosis of Injury from Defoliating Insects 



A. Trees sickly, leaves not chewed but yellowing or covered with a 



sticky exudation or black smut Sap-sucking insects, p. 55 



B. Leaves stunted, galled, or swollen Gall makers, p. 68 



C. Foliage appearing thin or sparse. Leaves chewed, mined, skeleton- 



ized, or stripped from trees. 



1. Leaves chewed more or less indiscriminately or skeleton- 



ized. Defoliated part of tree not covered with silken 

 webbing. Free feeders. 



a. Work done by typical caterpillars with three pairs 

 of true legs, four pairs of medium prolegs, and 

 one pair of anal larvapods. 



(1) On conifers. ■■ 



aa. Stout, yellowish-green or brown, 

 leathery caterpillars, 2 to 3 inches 

 long, with short, dark hairs and 

 seven or eight stout, branched 

 spines on nearly every segment 



Pandora moth, p. 83 



(2) On broad-leaved trees and shrubs. 



aa. Large, stout caterpillars with 



sparse, stout tubercles, and scat- 

 tered spines Giant silk moths, p. 82 



66. Yellow and black caterpillars with 

 branched spines 



Brown day moth, p. 86 



cc. Black caterpillars with fine, 

 branched spines on each segment, 

 middle row of spines bright yel- 

 low; on Ceanothus 

 California tortoise shell butterfly, p. 210 

 6. Work done by naked slugs with three pairs of true 

 legs and six to eight pairs of prolegs; one end of 

 body frequently held in midair when disturbed 



Sawflies, p. 116 



(1) On conifers. 



aa. Larvae in nests of webbing and 

 frass; on Monterey pine 



Itycorsia spp., p. 120 

 66. Larvae solitary or gregarious, not 

 in nests of webbing and frass: 



On pines Neodiprion spp., p. 118 



On western hemlock 



N eodriprion tsugae, p. 120 

 On western larch 

 A?ioplonyx and Pristophora, pp. 120, 122 



(2) On broadleaved trees Cimbex, etc., p. 122 



c. Work done by active grubs with three pairs of true 



legs, or by hard-shelled beetles Leaf beetles, p. 124 



(1) On conifers, needles chewed to leave scal- 



loped or sawtoothed edge: 



On pines. Dichelonyx and Scythropus, p. 125 

 On white fir Thricolepsis, p. 125 



(2) On broadleaved trees, leaves skeletonized 



or chewed; on alder, poplar, and willow 



Altica, p. 123 

 Chrysomela, p. 124 

 Galerucella, p. 124 



2. Leaves chewed, and defoliated part of tree covered with a 



light silken webbing; work of caterpillars with three 

 pairs of true legs and less than six pairs of prolegs. 



