THE GENUS DENDROCTONUS. 



53 



No. 3. THE ROUNDHEADED PINE BEETLE. 



(Dendroctonus convexifrons Hopk. 



15-17.) 



The roundheaded pine beetle is a somewhat elongate cylindrical, 

 reddish-brown to black, rather shining barkbeetle, 4 to 6 mm. in 

 length, with the front of the head convex, and without frontal groove, 

 the prothorax broad, only slightly narrowed toward the head, and 

 finely punctured, the elytra with coarse rugosities toward the base, 

 and the declivity with fine punctures and long erect hairs. (See fig. 

 15.) It attacks injured, felled, and healthy western yellow pine from 

 southern Arizona to northern New Mexico and southern Colorado. It 

 excavates long, slightly winding, longitudi- 

 nal, and sometimes transverse and branched 

 egg galleries (fig. 16) extending through the 

 inner living and dying bark and grooving 

 the surface of the wood. At intervals 

 along the sides of the galleries single eggs 

 are deposited. The short, cylindrical, grub- 

 like larvae extend their larval mines at right 

 angles to the egg galleries, usually through 

 the inner layers of bark, and mark the sur- 

 face of the wood. The transformation to 

 pupae and adults is sometimes in the inner 

 bark, but probably more often in the outer 

 bark. This barkbeetle is nearly always as- 

 sociated with one or more of four other 

 species of Dendroctonus — Nos. 2, 3, 5, 8, 

 and 10. The presence of this species is 

 indicated by pitch tubes on the trunk and 

 by the fading and reddish foliage. 



Fig. 15.— The roundheaded pine 

 beetle {Dendroctonus convexi- 

 frons): Adult. Greatly enlarg- 

 ed. (Author's illustration.) 



SEASONAL HISTORY. 



OVERWINTERING STAGES. 



The winter is passed in the bark of trees attacked the preceding 

 summer, as parent adults, young to matured larvae, young adults, 

 and possibly pupae, the parent adults in the egg galleries, and the 

 broods in the outer and inner bark. 



ACTIVITY OP OVERWINTERED BROODS. 



The overwintered parent adults extend the old galleries or excavate 

 new ones from the time activity begins in May until the last of June, 

 or later. The overwintered broods of young adults begin to emerge, 

 probably, in June, and continue to come out until September. The 

 overwintered larvae begin to transform to pupae and adults in June 

 and apparently continue to develop and transform to adults until 

 activity ceases in the fall. Some of the adults which have transformed 



