BUREAU OF ENTOMOLOGY AND PLANT QUARANTINE 43 
face of wood in a 3-minute dip. This latter combination continued 
to furnish protection after two years' exposure of the treated wood 
to direct contact with the soil. 
Organic residual insecticides such as benzene hexachloride, chlor- 
dane, and DDT have been found effective in controlling active infesta- 
tions of drywood termites and in preventing subsequent attack. When 
applied to the surface of wood containing infestations near the sur- 
face they have given excellent control. When injected under low 
pressure into wood containing deep-seated infestations they have also 
given excellent control. When these materials are dissolved in liquids 
capable of penetrating wood to a slight degree they have been found 
to enter and follow termite galleries where they are eventually de- 
posited in the form of crystals. These may kill by direct contact 
or by fumigation. This is especially true with benzene hexachloride. 
Natural Parasites Survive DDT Spraying for 
Spruce Budworm Control 
The effect on natural factors of control — particularly parasites — 
of aerial sprays applied in Oregon to control the spruce budworm 
was determined. Observations during 1951 in areas sprayed in 
1949 and 1950 showed that most parasites were present in these areas; 
furthermore that the percentage of parasitization of overwintering 
budworm larvae was actually higher in the sprayed than the unsprayed 
areas. The studies strongly indicate, therefore, that airplane spray- 
ing with DDT did not eliminate budworm parasites in the treated 
areas. 
■ 
Better Methods of Aerial Detection of Forest Insect 
Infestations Developed 
More accurate, rapid and economical methods of detecting and 
appraising forest insect infestations in the eastern United States 
by aerial surveys were developed in work performed in Maine in 
cooperation with the State. One phase of the study consisted of 
using a line-strip survey method and recording on a moving chart the 
extent of spruce budworm defoliation of balsam fir. Approximately 
0.7 percent of the entire area of some 10 million acres was surveyed 
in 23.7 hours of actual flying time. The flight crew consisted of a 
pilot and two observers. The cost of the operation was only $0.18 
per 1,000 acres. It was shown, therefore, that spruce budworm in- 
fested forests could be surveyed faster, more intensively, and more 
economically from the air than from the ground. A second phase 
of the study consisted of testing the value of stereo color photographs 
in appraising white pine weevil damage in plantations, especially 
in the taller stands of pines where height and density of crowns 
interfered with observations from the ground. An analysis of results 
showed that infested trees could be photographed from the air with a 
satisfactory degree of accuracy. 
Higher Altitudes Specified for Aerial Spraying for 
Spruce Budworm Control 
Tests were made to determine the feasibility of decreasing the 
hazard of low flight over forests in airplane-spraying operations by 
increasing the altitudes of flights. Tests were made of spray distribu- 
