re 
caused some mortality of the gypsy moth but the results were 
inconclusive. Higher mortalities of two species of loopers (EHran- 
mis tiliaria and Phigalia titea), which also were present in the 
sprayed areas, were recorded. 
CHEMICAL CONTROL 
The use of chemicals to suppress forest insect populations is a 
method of last resort. It is the policy to use them only when other 
forms of control, either natural or artificial, fail or threaten to fail 
in the prevention or control of destructive populations. Depending 
on the situation, chemicals may be applied to a single tree or to 
forested areas covering thousands of acres or square miles. The 
aim, therefore, is usually limited to the suppression of injurious 
populations to tolerable levels. 
Many different types of equipment and techniques are available 
for applying insecticides (601). Aerial applications are made by 
fixed-wing aircraft (fig. 3) or helicopters to large areas (29, 214, 
57, and 392). Individual trees, small groups of trees, and seed 
orchard trees (fig. 4) may be treated by ground equipment such 
as mist blowers (602) or by knapsack sprayers. Large individual 
trees may be treated by mist blowers and by hydraulic sprayers. 
Logs are treated by power sprayers. Fogging machines are 
sometimes used around resorts and campgrounds. Chemicals 
may be introduced into the tissues of living trees for bark beetle 
control (171, 52, and 762). Systemic insecticides may be applied 
by trunk implantation or injection, by banding or spraying of the 
circumference of the trunk, by spraying the foliage, by treating 
the soil around the base of trees, or by dipping cuttings prior to 
plantine= (570-587-199, 515, 36, and 447). 
The effectiveness of chemicals in suppressing many forest insect 
populations has been amply demonstrated during the past 25 years 
er 3 Rah 
F-482299 
FicgurRE 3.—Airplane spraying for spruce budworm control 
25 
