INSECT ENEMIES OF WESTERN FORESTS 155 



legs but are somewhat grublike in form. Pupation occurs within 

 the larval gallery, and when about ready to change to the adult the 

 pupa works partially out of the burrow, so after emergence the 

 empty pupal skin is found protruding from the tunnel. 



The carpenter worm {Prionoxystus rohiniae Peck) (fig. 77) is the 

 most common representative of this group. It attacks oak, elm, 

 poplar, Cottonwood, locust, ash, maple, willow, and other ornamentals 

 and also fruit trees and is distributed generally throughout the 

 United States. As is the case with the carpenter moths, these moths 

 cause injuries that show up later as defects in the lumber, since they 

 mine in the sapwood and heartwood of trunks and limbs. It is prob- 

 ably the most destructive insect enemy of oaks in California. The 

 adult females are gray moths with a wing expanse of from 2 to 3 

 inches. The males are smaller, with the front wrings dark gray and 

 the hind wings yellowish red lined with black (fig. 77). The mature 

 larvae are about 2i/2 inches in length, somewhat pinkish, with a dark 

 head and with scattered hairs arising from small brown spots on the 

 body. Eggs are laid in June and July, each female depositing from 

 200 to 300. Three years are required to complete the life cycle. 



Another species, Acossus populi Walk., does similar work in pop- 

 lars and Cottonwood. Givira lotta B. and McD. works in the outer 

 heavy bark at the base of ponderosa pines in Colorado. 



HORNTAILS OR WOOD WASPS 



(Siricidae) 



The horntails, or wood wasps, are injurious to the green, un- 

 seasoned or moist wood of practically all western conifers. Fre- 

 quently serious damage is done, especially to the wood of fire-killed 

 trees. Sometimes redwood lumber is attacked and injured, even 

 after it is cured and placed in storage yards. 



The adult females are thick-waisted, cylindrical wasps, with two 

 pairs of wings and a hornlike ovipositor, which resembles a stinger, 

 at the rear of the abdomen. They are usually of metallic colors — 

 dark blue, black, or marked with orange and red. The females 

 alight on freshly felled injured or dying trees and with great dex- 

 terity insert their long flexible ovipositors deeply into the wood, 

 often for an inch or more, and lay their eggs. Sometimes they 

 are unable to extract their ovipositors from the wood and die in 

 this position. The larvae which hatch from the eggs are cylin- 

 drical and yellowish white, with a small spine at the posterior end 

 of the body, and they sometimes hold their bodies in the shape of a 

 shallow letter S. They are truly wood-eating in habit and work 

 in the solid wood without any opening extending to the outside. 

 As they feed they make perfectly circular holes in the wood and 

 pack their boring dust in the tunnels behind them. It takes one 

 or two seasons for them to complete their development. Pupal cellsi 

 are constructed near the surface of the wood, and when the adults 

 mature, they cut round, clean-cut emergence holes to the surface 

 through which to escape. 



Prompt utilization of unseasoned wood exposed to attack by 

 these insects is the best means of avoiding damage. Logs placed 

 in mill ponds and frequently rolled will not suffer from attacks. 

 Kiln-drying gives complete control, destroying the infesting larvae, 



