258 AXInUAL REPOKTS of DEPALTAIENT of AGRICULTUrvE. 



INVESTIGATIONS OF INSECTS AFFECTING FOREST RESOURCES. 



The work in forest entoinology has been continued during the past 

 year under the direction, as before, of Dr. A. D. Hopkins. The 

 results accomplished by this section of the bureau deserve especial 

 mention and justify the expenditure of a larger sum of money in this 

 direction. 



WESTERN FIELD WORK. 



An especial investigation of the insect damage to crude spruce 

 products for airplane stock in the States of Washington and Oregon 

 showed that the greater part if not all of the damage could be pre- 

 vented by proper methods of logging and production with little or no 

 additional cost. 



Exhaustive studies of insect investigation and control were con- 

 tinued in the Sequoia and Yosemite National Parks. Much new in- 

 formation has been gained, and the methods of gathering and com- 

 piling field data have been standardized. 



A special stud}^ was completed on the interrelation of forest fires 

 and insects on an area of about 8,000 acres in southern Oregon. This 

 area had been under observation since 1914, and the fire had burned 

 over about 800 acres in 1918. The records show that previous to the 

 fire the insects had killed 485,000 board feet of timber. The fire 

 killed 170,000 feet, and subsequently the slightly fire-injured as well 

 as the uninjured trees in the burned area were killed by beetles, 

 wliich were attracted from the surrounding areas. It was noticed 

 that the infestation in the burned area increased more than 1,000 per 

 cent, but it was found that the infestation in the surrounding areas 

 decreased. It was also found that the broods of the beetles in the fire- 

 scorched trees failed to develop to much beyond the original number 

 that attacked the trees. So the fire did not contribute to an increase 

 of the beetles in the general area or to the starting or extension of an 

 epidemic of beetles. This result is of extreme interest and hardly to 

 be expected. 



The most careful study ever made of the history of an epidemic 

 infestation b}^ tree-killing beetles was completed and a report sub- 

 mitted during the year. In the Rogue River area in about 48,000 

 acres near Ashland, Oreg., the western pine beetle in 1914 caused 

 the death of 346,000 board feet of pine timber. In 1915, 1,615,000 

 board feet Avere killed; 1,383,000 feet in 1916; and 608,000 in 1917. 

 A count of the young and matured stages of the beetles that de- 

 veloped in an average foot of bark, and also of the number of exit 

 holes through which the beetles emerged to attack other trees, showed 

 that there was a notable decrease in numbers during the develop- 

 ment of the broods each year in the infested trees on account of the 

 increase of natural enemies and other disturbing factors. This helps 

 explain why these beetle epidemics rise and fall within a limited 

 period of years, and it explains how the w^estern forests of yellow 

 pine are naturally protected from total destruction. These facts are 

 especially significant in connection with the application of the 

 percentage principle of control, as by aiding the natural forces which 

 work against the abnormal increase and spread of the beetles com- 

 plete control may be gained. The history of this epidemic shows the 

 ]mx)ortance of prompt recognition and prompt treatment of a threat- 



