4S MISC. PUBLICATION 657, U. S. DEPT. OF AGRICULTURE 
The application of measures for the control of bark beetles may be 
justified by such factors as the value and merchantability of the tim- 
ber, the preservation of the forest cover as a watershed-protection 
measure, the elimination of fire hazards, and the prevention of the 
spread of the beetles into adjacent stands of timber. The results to 
be obtained must be balanced against the cost of the operation to 
determine whether the project is : economically justified. 
Successful bark-beetle control depends primarily on early detection 
of the outbreaks and prompt application of effective control measures. 
This is particularly important in the East because of the quick rise 
and decline of the outbreaks of the eastern bark beetles. Almost 
without exception, outbreaks of these insects occur during a period 
of deficient rainfall. Usually a deficiency of an inch or more for 2 
months or longer during the active season is sufficient to bring about 
conditions favorable for outbreaks, and those charged with the pro- 
tection of timber should make systematic observations of susceptible 
areas whenever such deficiencies in rainfall occur. This is particularly 
true of the southern pine beetle, the hickory bark beetle, and species of 
Ips. 
The relationship between deficient rainfall and spruce bark beetle 
occurrence has not been so clearly demonstrated, although the first 
signs of an outbreak are usually to be noticed on exposed ridges or poor 
sites, where the effects of the drought are most extreme. 
BARK BEETLE SURVEYS 
Upon the first evidences of fading foliage, a survey of the entire 
susceptible area should be undertaken in order that the extent and 
character of the infestation may be determined and sound plans be 
formulated for any control operations found necessary. Several meth- 
ods of making surveys are available, each of which has certain 
advantages. 
The simplest and least expensive type of survey is made by viewing 
the country from lookout points and making counts of the infested 
trees from roads or trails. Observation from airplanes for evidences of 
fading foliage is also an excellent means of early detection. Sample 
strips: run at intervals back and forth across infested areas @ive a very 
comprehensive estimate of the amount and distribution of infestation, 
and where time and money are available they unquestionably furnish 
the most satisfactory basis for an estimate of costs. 
The cruising of sample plots has its place as a supplement to topo- 
graphic viewing, and with small units it is often possible actually to 
survey a rather large percentage of the area in this way. Where large 
areas of diverse topography include a number of different forest types, 
several different methods or combinations of methods of estimating 
may be used. Too often there is a tendency to examine too small an 
area and consequently to obtain an incomplete picture of the magni- 
tude of the infestation. 
THE CONTROL UNIT 
The size of the area in which control operations should be carried 
out depends on the extent of the infestation. It is often entirely futile 
for one owner to do control work on his land if no work is done on 
adjacent infested properties. Every effort should be made to clean up 
