INSECT ENEMIES OF WESTERN FORESTS 



145 



Figure 65. — Posterior ends of six species of Ips, showing number and 

 arrangement of spines: A, ponderosae Sw.; B, lecontei Sw.; C, plasto- 

 graphus (Lee); D, knausi Sw. ; E, emarginatus (Lee); F, radiatae 

 (Hopk.). All greatly enlarged. (Drawing by Edmonston.) 



eral females then join in the work and each constructs an egg- 

 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 

 egg galleries, leaving gradually widening, excrement-packed tun- 

 nels behind 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. The period from the time of attack 

 to the emergence of the new brood is ordinarily 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 considerable overlapping of generations. The winter is 

 usually spent in the adult stage, although occasionally eggs, larvae, 

 and pupae are found. 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 predaceous and parasitic 

 enemies, but apparently these do not affect the numbers of the 

 beetles so much as does the lack of suitable host material. Given a 

 quantity of freshly cut slash or windfalls, a large beetle popula- 

 tion is almost certain to be produced but it will not long survive 

 after the supply of this material is exhausted. 



