THE GENUS DENDROCTONUS. 77 



No. 8. THE COLORADO PINE BEETLE. 



(Dendroctonus approximates Dietz. Figs. 40-43.) 



The Colorado pine beetle (fig. 40) is a somewhat elongate, cylin- 

 drical, dark brown to black barkbeetle, 4 to 7.4 mm. in length, 

 with broad, deeply grooved head; prothorax broad, punctured, and 

 but slightly narrowed toward the head, and elytra with dense, mod- 

 erately coarse rugosities, the declivity with coarse punctures and long, 

 nearly black, erect hairs. It attacks injured, dying, and healthy west- 

 ern yellow pine, from central Colorado and Utah to southern Arizona 

 and New Mexico. It excavates long, slightly winding, longitudinal 

 and sometimes transverse, and branched egg galleries through the 

 inner living and dying bark, and grooves the surface of the wood 

 (fig. 41); the larval mines are usually concealed beneath the inner 

 bark and the larvae usually transform to pupae and adults in the 

 outer bark. It is nearly always associated with one or more of 

 species, 2, 3, 5, and 10 in the same tree. 



SEASONAL HISTORY. 



OVERWINTERING STAGES. 



The winter is passed as parent adults, young adults, young to 

 matured larvae, and possibly pupae — the parent adults in the egg 

 galleries in the inner bark and the broods in the outer bark of trees 

 attacked the preceding summer. 



ACTIVITY OF OVERWINTERED BROODS. 



From the beginning of warm weather until in June the over- 

 wintered parent adults extend their old galleries and excavate new 

 ones and deposit eggs. The overwintered broods of young adults 

 begin to emerge from the trees early in June and continue to come 

 out until September or later. The overwintered broods of larvae 

 probably begin their transformation to pupae and adults in June 

 and continue to do so until September or later. The adults begin to 

 emerge in June, but their principal period of emergence is in July, and 

 they continue to come out until September or later. It is probable 

 that some individuals or broods which pass the winter as young 

 larvae may be retarded in their development and pass the second 

 winter as matured larvae or adults. 



GENERATION. 



The overwintered broods of young adults evidently begin to 

 attack the trees, excavate galleries, and deposit eggs early in June, 

 or earlier in their southern distribution. The principal attack is in 

 June, July, and August, but they continue the attack until Septem- 

 ber or later. Some of the broods from eggs deposited in June may 

 develop to adults in September, but it appears that they do not 

 emerge and that the majority of the broods of this generation pass 

 the winter as larvae, } r oung adults, and parent adults. 



