INSECT ENEMIES OF WESTERN FORESTS 33 



Key to Diagnosis of Insect Injury to Young Trees (Cont,) 



B. Terminal shoots, laterals, or tips deformed or killed. Trees 

 weakened or stunted but seldom killed (except seedlings and 

 small saplings). 



1. New or old twigs, branches, or succulent shoots killed. 

 Insect tunnels or borings found under the bark. 



a. Point of attack showing a small, reddish pitch tube 



with exudation of fine boring dust and pitch. 

 Under the bark or in pith of twigs are found 

 small egg tunnels of uniform width, free from 

 packed boring dust, made by small brown 

 beetles; and larval tunnels packed with fine bor- 

 ings made by small, white, curled, legless larvae 



Twig beetles, p. 36 



b. Point of attack on green stems showing a small, 



clear pitch globule. Tunnels under bark, nearly 

 round, free from pitchy exudations, filled with 

 coarse or powdery boring dust. Made by small, 

 white, curled, legless grubs Twig weevils, p. 39 



(1) Borings scoring sapwood rather super- 



ficially; boring dust coarse; pupal cells 

 lined with shredded wood fiber 



Pissodes spp., p. 39 



(2) Borings deep in wood; boring dust fine- 



grained and powdery; pupal cells oval 



and smooth Magdalis spp., p. 41 



(3) Small, round open holes in bark and 



wood; pupal cells formed in pith or 

 wood, without lining but plugged with 

 fine borings Cylindrocopturus spp., p. 42 



c. Point of attack not conspicuous. Tunnels under 



bark broadly oval or nearly flat and filled with 

 boring dust. Made by slender white grubs with 

 broad heads Twig borers, p. 46 



d. Bark and wood of twigs conspicuously gnawed and 



girdled, causing death and breakage 



Twig girdlers, p. 46 



e. Resinous tunnels made by active caterpillars under 



bark or in the shoots; point of attack showing 

 resinous exudation, with larval castings webbed 

 together, or pitch nodule Twig or tip moths, p. 48 



(1) Large reddish- or brownish-green to dirty- 



white caterpillars (3/4 to 1 inch long at 

 maturity), boring into cambium of 

 branches, twigs, or cones. Entrance indi- 

 cated by webbed larval castings, fol- 

 lowed by exudation of pitch 



Twig moths, Dioryctria spp., p. 48 



(2) Yellow, brown, or reddish caterpillars, 



about 1/2 inch long at maturity, start 

 feeding around bases of needle fascicles 

 on terminal shoots, then bore into ter- 

 minal buds and down into new growth. 

 Work characterized by resinous exuda- 

 tion at point of attack and death of ter- 

 minal bud and needles at apex of shoot 



Pine tip moths, Rhyacionia spp., p. 50 



(3) Small, pale brown, or reddish to white 



caterpillars (1/2 inch long when ma- 

 ture) feeding on twigs and branches at 

 nodes or whorls of branches causing a 



