42 



THE SCOLYTID BEETLES. 



No. 1. THE WESTERN PINE BEETLE. 



{Dendroctonus brevicomis Lee. Figs. 6-1L) 



The western pine beetle is a rather stout, brownish, cylindrical bark- 

 beetle, from 3 to 5 mm. in length, with head broad and grooved, 

 pronotum punctured and but slightly narrowed toward the head, 

 and elytra with fine rugosities, but entirely without long hairs. 

 (See fig. 6.) It attacks healthy, injured, and felled western yellow 

 pine and sugar pine, and is destructive to living timber in the moun- 

 tains of California and northward and eastward to Washington and 

 Montana. The adults excavate long, winding egg galleries (fig. 7), 

 through the inner layers of living and dying bark. The white, 

 legless larvae hatching from the eggs excavate short larval mines in 

 the middle portion of the inner bark, the latter rarely showing on 



Fig. 6. — The western pine beetle (Dendroctonus brevicomis): Adult, larva, pupa, greatly enlarged. 

 (Adult and larva, author's illustrations; pupa, from Webb.) 



the inner surface. Later they transform to pupse and adults in the 

 outer corky bark. Pitch tubes (figs. 8, 9) are produced on the main 

 trunk of the living trees attacked. The fading to yellowish and 

 reddish foliage indicates its destructive work. 



SEASONAL HISTORY. 



OVERWINTERING STAGES. 



The broods pass the winter in the outer bark of trees attacked the 

 preceding late summer and fall, as parent adults, young adults in 

 pupal cases, all stages of larvae, and possibly pupa?. 



ACTIVITY OF OVERWINTERED BROODS. 



The overwintered parent adults extend their galleries or excavate 

 new ones and deposit eggs during April and May, from which broods 

 develop and emerge by the last of July to the middle of August. 



