INSECT ENEMIES OF EASTERN FORESTS 19 
ther information is available from the following sources: United States 
Bureau of Entomology (476, 4/7), Munns (313) , Munns and Coville 
(37/4), and Craighead (7/5). 
IN MATURE TIMBER 
It is common knowledge that overmature timber is difficult to pro- 
tect. In a way, insects are one of nature’s agencies for harvesting 
mature timber, thus clearing the way for new erowth, With shorter 
rotations in the future, losses in mature timber should be greatly 
reduced. Systems of selective cutting have been devised for ponder osa 
pine in the West, based on the oreater susceptibility of certain types 
of trees to bark beetles. Recently it has been found necessary to cut 
overmature stands of spruce in Vermont to avoid losses by the spruce 
bark beetle. 
IN SECOND GROWTH 
In contrast to the susceptibility of overmature stands, second- 
growth stands, particularly those of good vigor, are more able to 
resist insect invasion and are seldom totally destr oyed. The produc- 
tion of pulpwood in New England, the Lake States, and the adjacent 
rovinces of Canada is largely dependent on the control of the spruce 
udworm. The mortality in spruce and fir stands when attacked by 
this insect is lessened if the trees are in vigorous growth at the time of 
defoliation. 
FOREST COMPOSITION 
The composition of the forest is of prime importance in inviting or 
avoiding disaster. Recent destructive outbreaks of the spruce bud- 
worm in Minnesota, New England, and Canada are attributed to the 
great proportion of balsam fir in the stands, due to a hundred years of 
selective cutting of pine and spruce and to natural forest succession. 
The gypsy moth is a pest that must be reckoned with in the man- 
agement of the hardwood forests in New England. Fortunately seri- 
ous defoliation is restricted to areas having a high percentage of cer- 
tain favored species, and the management ‘of the forest to hold these 
favored hosts in the minority will prevent damage by this insect. 
Groupwise stands of white pme and hardwood are rarely badly in- 
jured by the white-pine weevil, whereas adjacent pure pine stands are 
often so heavily attacked that their future value for clear lumber is 
destroyed. 
Outbreaks of the southern-pine beetle are notably less severe where 
hardwoods form a considerable percentage of the stand. This calls 
for practices favoring the increase of hardwood species 1n those stands 
under management. In general, the planting or the encouragement 
of great blocks of a single species is to be avoided except where the 
climax type is such as is “found in the pineries of the coastal plains of 
the South, which are notably free from serious insect outbreaks. 
Such mixtures of species as those that nature tends to work toward in 
the climax types of an area should be the goal. The transition types of 
trees should be utilized early, before insect outbreaks take their toll. 
THINNINGS 
Sudden drastic changes affect trees unfavorably and make them 
susceptible to attack. For this reason the opening of the stand through 
logging favors the subsequent attack on certain trees by such insects 
