INSECT ENEMIES OF WESTERN FORESTS 27 



The adults of cutworms are the dull-colored, yellow, tan, or brown 

 moths which collect around lights at night and are commonly re- 

 ferred to as "millers." They fly at night, usually early in the spring, 

 and lay their eggs on the ground where there is ample vegetation for 

 larval food. The larvae or cutworms work underground, feeding on 

 the roots of various plants, or during the night they often feed above- 

 ground on the foliage or clip off the stems at the ground line. They 

 are dull-colored, with very few or sometimes no hairs on the body, and 

 some have a greasy, slimy appearance that is in keeping with their 

 ground habitat. They reach full growth late in the summer or in the 

 fall and overwinter in the soil as full-grown larvae or as pupae in 

 earthen cells. Emergence takes place the following spring, or in 

 some cases there may be several broods a year. 



Clean culture in the nursery to avoid the establishment of weeds or 

 ground cover that would be suitable for egg-laying, and cultivation 

 in the fall and winter to destroy the hibernating larvae, will do much 

 to prevent cutworm damage. Where such methods fail, poisoned 

 baits made of bran and white arsenic are effective. A good formula 

 for this purpose is as follows : 



Wheat bran 25 pounds. 



White arsenic or paris green 1 pound. 



Blackstrap molasses 1 quart. 



Water 1 to 2 gallons. 



Where seedbeds can be flooded for a time without damage to the 

 young trees, cutworms can be drowned. Such treatment is often both 

 simple and effective. 



ROOT BARK BEETLES 



Although bark beetles (Scolytidae) are primarily enemies of large 

 forest trees, a few species are of importance in killing large seedlings 

 through attack on the roots. Species of the genera Hylastes and 

 Hylurgops have been found doing this type of damage. Normally 

 these are secondary bark beetles which breed in slash and under the 

 bark of trees killed by fire or insects, but they appear to be primary 

 in attacking the roots of suppressed or weakened seedlings. The 

 attacking beetles make entrance burrows at the ground line and con- 

 struct winding galleries which extend downward into the larger 

 roots and are partly filled with f rass. The larvae work through the 

 cambium, away from the ^gg tunnels, and feed together without scor- 

 ing the wood. Seedlings an inch op more in diameter are killed by 

 the attacks. The species which have been found doing this type of 

 damage are noted below: 



Species Hosts 



Hylastes nigrinus Mann Douglas fir, western white pine, western 



hemlock, and probably other conifers. 

 Hylastes macer Lee Engeimann spruce, ponderosa pine, and 



lodgepole pine. 



Hylurgops lecontei Sw , — Lodgepole pine, ponderosa pine. 



Hylurgops porosus Lee .. Lodgepole pine, western white pine, and 



probably other pines. 

 Pseudohylesinus granulatus Lee Balsam firs. 



The general habits of bark beetles are more fully discussed in a 

 later section (page 96). 



