Adult weevils usually confine their damage to crop trees within thinned stands. 

 However, if a young unthinned stand borders the thinned area, weevils often damage 

 trees along the periphery of the unthinned area. Seldom though will damage extend 

 more than 15 or 20 feet from the thinning area boundary. However, weevils do not 

 damage foliage of mature trees bordering thinned stands even where crop trees are 

 heavily damaged. 



In one instance, weevils were attracted to an area where logging slash--composed 

 of treetops and limbs --accumulated following clearcutting for posts and poles. They 

 fed on foliage of young lodgepole pine along the periphery of a dense unthinned stand 

 adjoining the clearcut, because there were no young crop trees on which to feed. 



There appeared to be no relationship between incidence of weevil damage and the 

 height or size of crop trees--damage was evident throughout the crown. In one 

 thinning, heavily infested crop trees varied from 1.5 to 6 feet tall and from one-half 

 to 3 inches in diameter (at a point 1 foot above the ground). In other thinnings, 

 weevils damaged crop trees 15 feet tall. Another species of Magdalis, M. perforatus 

 Horn, attacks trees of all ages but adult weevils prefer to oviposit and feed on trees 

 under 10 or 12 feet in height in red pine (Pinus resinosa Ait.) plantations in Ontario, 

 Canada (Martin 1962, 1964). 



Two observations were made suggesting that M. gentilis adults might prefer a more 

 open and/or less shaded environment. Many young thinned stands were surrounded by 

 stands of mature lodgepole pine. In such cases, trees near the edge of the thinned 

 area, which at times were shaded by the adjacent uncut stand, usually suffered less 

 weevil injury than unshaded trees toward the center of the thinned stand. A second 

 observation was made in an experimental area where trees had been thinned at inten- 

 sities varying from 6 by 6 feet (1,200 trees/acre) to 18 by 18 feet (150 trees/acre). 

 Examinations of 144 trees in this study area in August 1965 indicated that crop trees 

 in the more intensely thinned plots were more severely damaged (fig. 9). 



5r 



4 6 8 



NUMBER OF CROP TREES (100/acre) 



10 



12 



Figure 9. — Relationship of needle damage by Magdalis gentilis LeC. to the number of 

 lodgepole pine crop trees per acre, Lewis & Clark National Forest^ Montana. 

 (See tabulation^ page 10.) 



11 



