122 



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



The usual method of direct control is to fell the tree and cut the 

 infested bole into logs, which are then decked and burned. As a 

 large percentage of these insects overwinter as adults and emerge 

 early in spring, fall control is the most effective. 



THE FIR-ENGRAVER BEETLES 



There are a number of small species of bark beetles, belonging to 

 Scolytus, PseudohyJesimis^ and other related genera, which commonly 

 work under the bark and score the sapwoocl of dying, broken, or felled 

 firs, but which at times may become so abundant and aggressive as to 



attack and kill small trees. This 

 entire group may be referred to 

 as "fir engraver beetles." 



Members of the genus Scoly- 

 tus^ are small, shiny, dark, or 

 nearly black bark beetles, which 

 are easily recognized by the con- 

 cave appearance of the posterior 

 ventral surface of the abdomen. 

 The adults feed for some time 

 by making feeding pits in the 

 twigs and later attack in pairs 

 and construct short ^gg gal- 

 leries, usually from a central en- 

 trance chamber. The larvae 

 work out at right angles from 

 the egg gallery and bore through 

 the phloem and inner bark, usu- 

 ally deeply scoring the sapwoocl. 

 Some members of the genus are 

 exceedingly destructive to bal- 

 sam firs. Others work in Doug- 

 las fir, hemlock, spruce, or even 

 in broadleaved trees. 



The Douglas fir engraver 

 {Scolytus unispinosus Lee.) is 

 commonly found attacking 

 weakened, injured, dying, or re- 

 cently killed Douglas fir in the 

 Pacific Coast and Rocky Mountain States and soutliAvestern Canada. 

 Sometimes it is a primary enemy of 3^oung Douglas firs. The 

 adults are small, black, cylindrical, shining bark beetles about one- 

 eighth inch in length, with a long spine projecting from the middle 

 of the nearly perpendicular face of the ventral declivity. The 

 tj^pical egg gallerj^ follows the grain of the wood and may range 

 in length from 1^ to 3 inches. A short entrance tunnel leads into 

 the main gallery, at an angle of 45°, and a small nuptial chamber 

 is constructed at the juncture (fig. 60). The larvae work out at 

 more or less of a right angle from the egg gallery, and then work 

 up or down the tree so that the mines will not cross one another. The 

 winter is spent in the egg and young larval stages. Emergence of 

 adults takes place late in April, in May, June, and July. There 

 appear to be two generations annually. 



Figure 6U. — Work of the Douglas fir en 

 graver {Scolytus unispinosus) . 



