472 



Yearboo^ of Agriculture 1949 



disadvantage in all these attempts was 

 that only the severe infestations could 

 be detected; the lightly infested areas 

 could not be distinguished, with the 

 equipment of that time, from the areas 

 that were uninfested. 



From 1925 until the outbreak of 

 the Second World War, periodic at- 

 tempts were also made to use air sur- 

 veys in connection with bark beetle 

 control. Flights made over western 

 forests were disappointing. Dying trees 

 could be seen from the air, but equip- 

 ment had not been developed for 

 mapping accurately their location or 

 determining the type and size of trees 

 attacked. In the Eastern States, air 

 surveys were most successful for locat- 

 ing trees infected with Dutch elm; 

 disease, which is transmitted by elm 

 bark beetles. Observers flying at slow 

 speeds in an autogiro could easily de- 

 tect trees showing symptoms of the 

 disease and could pin-point their lo- 

 cation on a base map. 



MORE RECENTLY, the depletion of 

 forest resources during the war, the 

 greater need for more adequate con- 

 trol of forest insects, and the wartime 

 improvement in the aerial observation 

 methods gave further impetus to sur- 

 veys from the air. 



Three methods are used: Sketch 

 mapping, ocular estimating or strip 

 counting, and photographic sampling. 



The first is a "look-see" method 

 similar to that employed in the early 

 defoliator surveys. The area is covered 

 in a systematic pattern and observers 

 sketch in the boundaries of infested 

 areas on previously prepared maps. 

 Estimates of the extent of damage are 

 made as the mapping progresses. In 

 the Pacific Northwest an outbreak 

 covering more than 700,000 acres was 

 surveyed in this manner in 1947 at a 

 cost of about one-tenth of a cent an 

 acre. The method is still inadequate 

 for detecting very light defoliator in- 

 festations, but recent improvements 

 have made it a good way to get a quick, 

 rough estimate of the insect conditions 

 over a large area. 



Ocular estimating is being used 

 primarily for the bark beetle surveys in 

 western forests. In this method the 

 plane is flown along predetermined 

 lines over the forest. The observer 

 watches the ground through a port in 

 the bottom of the fuselage and counts 

 the number of dying trees in the sample 

 strip traversed. The estimates obtained 

 are then checked by limited ground 

 surveys at various points within the 

 forest area covered from the air. 



In photographic sampling, repre- 

 sentative localities within the forest are 

 photographed with a special aerial 

 camera. By taking pictures that over- 

 lap, stereoscopic methods can be used 

 to pick out the dying trees and to esti- 

 mate their size and crown characters. 



These new improvements have al- 

 ready widened the scope of forest- 

 insect surveys. Although the air surveys 

 still supplement rather than replace 

 ground methods, we expect that fur- 

 ther improvements, particularly those 

 in aerial photography, will make it pos- 

 sible to do more and more of the work 

 from above the forest instead of in it. 



INSECTICIDES were first applied from 

 the air in 1921, when a small infesta- 

 tion of catalpa sphinx in Ohio was con- 

 trolled by dusting lead arsenate from 

 an open-cockpit biplane. 



Soon afterwards, dust applications 

 were made in the United States and 

 Canada against the hemlock looper, 

 spruce budworm, and gypsy moth, and 

 in Europe against the nun moth, pine 

 looper, cockchafer, and other pests. 

 The results varied. The insecticide 

 dusts killed most of the different in- 

 sects, but the method of application 

 had three shortcomings : The dust was 

 frequently carried away by air currents 

 after release from the plane; the dust 

 particles did not stick to the tree foliage 

 and were quickly removed by strong 

 wind or rain ; and, with any of the in- 

 secticides known at that time, the 

 quantity of dust required made treat- 

 ing costs high about $7 an acre. 



Later, concentrated arsenical and 

 fluorine sprays were developed to re- 



