INSECT ENEMIES OF WESTERN FORESTS XI 1 



by these engraver beetles precedes and possibly attracts subsequent 

 infestation by DendroctonuH beetles. With the removal of mature 

 forests, to some it seems quite likely that this group of bark beetles 

 \Yill outrank the DendroctomiH beetles in destructiveness to the second 

 crop of pines. 



The Ips or engraver beetles 



The first evidence of attack by this genus is yellow or reddish 

 boring dust in bark crevices or little piles of such dust around the 

 entrance holes or on the ground beneath. Pitch tubes are seldom 

 formed, and the boring dust is usually dry and free from pitch. 

 Soon after a tree has been attacked the foliage fades and turns from 

 green to yellow, sorrel, and red. Upon removing the infested bark 

 the tunnels of the engraver beetles will be found grooving the inuer 

 bark surface and slightly marking the sapwood. The ^^^ galleries 

 differ from those of the Dendroctonus beetles in that instead of being 

 tightly packed with boring dust they are open runways in which the 

 adult beetles are free to travel the entire length. A second difference 

 is their polygamous social habit of constructing a central nuptial 

 chamber from which fork or radiate several ^^^ galleries. In many 

 cases the pattern of the completed work is sufficiently distinctive to 

 identify the species responsible. However, some species cannot be 

 recognized in this way and can be distinguished only by characters 

 in the adult beetles. 



The adults are small, reddish brown to black, often shiny, cylin- 

 drical bark beetles ranging from one-eighth to approximately one- 

 fifth of an inch in length. A distinguishing feature is the pro- 

 nounced concavity on the posterior end, which is margined with from 

 one to six pairs of toothlike spines. The small, white, legless larvae 

 differ slightly from Dendroctonus larvae in that the body is more 

 tapering and is thicker at the forward end than toward the rear. 



Attacks are made by these bark beetles with the coming of warm 

 weather in the spring. An adult male bores through the bark and 

 constructs a small cell or nuptial chamber in the inner bark. Several 

 females then join in the work and each constructs an ^^^ gallery in 

 which eggs are laid in niches along the sides. The larvae, upon 

 hatching, feed in the inner bark and work away from the ^gg galler- 

 ies, leaving gradually widening, excrement-packed tunnels iDehind 

 them. When their feeding is completed oval pupal cells are formed, 

 in which the transformations from larvae to pupae and then to adults 

 take place. From the time of attack until the emergence of the first 

 of the new brood ordinarily requires from 42 to 68 days. From two 

 to five generations of these beetles may develop during the summer, 

 depending on the altitude, latitude, and species, there being consid- 

 erable overlapping of generations. The winter is usually spent in the 

 adult stage, although occasionally in the ^gg or larval stage. Some 

 species congregate in large groups under the bark of standing trees 

 killed the previous year and feed to a limited extent on the dry, dead, 

 inner bark. Others emerge and hibernate under the bark of old 

 stumps, among the bark scales, or in crevices and litter at the base 

 of old brood trees. 



Engraver beetles have a number of predacious and parasitic ene- 

 mies but it appears that these do not affect the numbers of the beetles 



