INSECT ENEMIES OF WESTERN FORESTS 17 



group includes the leaf eaters, the cambium miners, and the wood 

 borers. Aphids, scale insects, and bugs suck plant juices by means 

 of slender mouth parts, which they insert into the tender portions 

 of the tree. A group of specialized insects irritate portions of the 

 tree and thus cause it to form a swelling or gall, which encloses 

 them. The method of feeding has an important bearing on the 

 methods of control. 



The important forest insects might be classified, for the purpose 

 of discussion, according to their natural relationships (45), ac- 

 cording to the species of trees attacked, according to the parts of 

 the tree affected, or according to the stage of the life of a forest 

 tree upon which they inflict their greatest injury. For the purposes 

 of this publication, it seemed that the last-mentioned classification 

 would be most helpful to the forest field man. In this publication, 

 therefore, the western forest trees will be followed through their 

 life cycle, from seed to final finished product, and at each step the 

 insects of greatest importance in injuring them will be discussed. 



INSECTS AFFECTING SEED PRODUCTION 



The natural reproduction of forests, the artificial reforestation 

 of denuded areas, and the future supply of timber depend to a 

 considerable extent on the production of a prolific supply of sound, 

 uninjured seed. In most instances insect damage to tree seeds is 

 not severe enough to be of great importance; in some seasons, 

 however, insects destroy practically all the seed of certain tree 

 species in certain localities. 



Destruction of seeds may be caused by insects that attack the 

 buds, flowers, or immature cones, as well as by those that attack 

 the seeds themselves. Damage at these early stages causes wilting, 

 blighting, or premature dropping of the parts affected. The fruit 

 or cones developing after insect attack may be deformed or 

 "wormy," riddled by the borings of various grubs, caterpillars, or 

 maggots. In many cases the cones show no damage, but the seeds 

 are infested with the small white larvae of seed chalcids. Even 

 the old, hard, dry cones of certain pines are often mined by wood 

 borers. The insects that affect seed production in these various 

 ways belong to a number of different orders and families, of which 

 some work only on cones or seeds, whereas others work also in 

 the bark or cambium of succulent growing shoots, stems, and 

 twigs, or even in dry wood. 



Knowledge of the presence of seed-infesting insects will often 

 prevent the disappointment and loss attendant on the collecting, 

 handling, and sowing of insect-damaged seeds (115). 



Key to Diagnosis of Insect Injury to Cones and Seeds 



A. Insects boring through fresh green cones and coniferous seeds. 

 1. Cones wither and die before they are half grown. 



a. Interior of pine cones mined by small, dark-brown 



beetles and small, white, curled larvae. .Cone beetles (p. 18) 



b. Fir, spruce, and other cones deformed and showing 



exudation of pitch or webbed borings; interior mined 



by active caterpillars Cone moths (p. 19) 



