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



Key to the Diagnosis of Insect Injury to the Inner Bark (Cont.) 



(1) In coniferous trees 



(aa) Dark reddish brown to black, shining beetles with 

 undercut abdomen; make one or two short longi- 

 tudinal or transverse egg tunnels from a well- 

 defined central nuptial chamber; in fir, spruce, 

 hemlock, or Douglas-fir. .Scolytus, pp. 157, 165, 166, 167 



(bb) Dull, dark-brown, roughened beetles with rear of 

 abdomen rounded; make one or two short longi- 

 tudinal or transverse egg tunnels without a well- 

 defined nuptial chamber. 



(bbl) In moist bark at base of pines. . .Hylastes, p. 154 



Hylurgops, p. 154 

 (bb2) In true firs, hemlock, spruce, Douglas-fir, 

 or pines. 



Pseudohylesinus, pp. 154, 155, 161, 162, 165, 166 



(cc) Small stout, dull brown to black beetles, with 

 rounded abdomen; make one (sometimes two) 

 short, longitudinal egg tunnels with well-defined 

 nuptial chamber at base; in cedar, cypress, red- 

 wood, and other cupressine trees. . . .Phloeosinus, p. 167 



(2) In broadleaved trees 



(aa) Egg galleries transverse (across the grain), 

 short, nearly straight. 



In oak. .Oak bark beetle, Pseudopityophthorus, p. 169 



In ash Ash bark beetle, Leperisinus, p. 169 



(bb) Egg galleries longitudinal (with the grain) ; 

 without enlarged entrance chamber. 



In alder Alniphagus, p. 169 



c. Egg galleries under bark not packed with boring dust; indi- 

 vidual galleries consisting of two or more tunnels forking 

 or radiating from a central entrance and nuptial chamber. 



(1) Egg galleries forking from a central nuptial chamber 

 with branches nearly straight and parallel (except at 

 start) ; mines 1/16 inch or more in width. 



(aa) Egg tunnels forking longitudinally; brood cham- 

 bers exposed in inner bark; cylindrical beetles 

 with spines around a concavity on the rear of 

 the wing covers Ips (in part) , pp. 144-151 



(bb) Egg tunnels forking transversely; brood cham- 

 bers concealed in inner bark Polygraphia, p. 166 



(2) Egg galleries radiating from central nuptial chamber 

 with branches slightly to strongly curved and not 

 parallel to each other. 



(aa) Large species; mines 1/16 inch or more in width. 

 (aal) Nuptial chambers scoring the sapwood 



Ips (in part), pp. 151, 152, 165 

 (aa2) Nuptial chamber not scoring the sapwood. 

 Galleries mainly longitudinal. 



Dryocoetes, pp. 163, 165 

 Galleries mainly transverse. Polygraphia, p. 166 

 (bb) Small species; mines less than 1/16 inch in width; 

 enlarged nuptial chamber; larval mines short and 

 club-like. 

 (bbl) Under thick, dry bark, mines often crossing 



those of Dendroctonus Orthotomicus, p. 153 



(bb2) Under thin bark; pines Pityogenes, p. 152 



2. Bark showing no outward sign of insect attack. Tunnels under 

 bark and sometimes entering wood; these increase in size with 

 the growth of the white, often legless grubs which make them. 



