28 ANNUAL REPORTS OF DEPARTMENT OF AGRICULTURE, 1 
l OBEST FEET r \ n BFHJ \u 
in the Lake States ;i control project against the forest tent caterpillar 
was carried on in Minnesota and Wisconsin. A number of powerful spraying 
.limits were purchased by the Forest Service and many hundreds of acres were 
sprayed. Particular emphasis was placed on control In recreational 
this \\«Tk was done in June 1986, do definite report as to results is yet available. 
RESEARCH ACTIVITIES 
EFFE4 is OF EXTBE1IS COLD ON WKSTKKN BABE BEETLES 
-• 1932 extreme cold has been recognized as a very important natural 
factor in limiting the numbers of some of our most destructive bark beetles. 
The degree Of low temperature producing this lethal effect Upon a particular 
species of bark beetle varies With the climatic conditions of the region from 
which the specimens come. Thus, in the case of the mountain pine I 
specimens grown in the southern Sierra region do not survive a temperature of 
2.5 I'., whereas members of the same species growing in the northern Rocky 
Mountains require as low a temperature as —17° for complete mortality. 
Careful field studies have demonstrated that the amount of mortality can be 
determined with fair accuracy from records of the minimum temperatu: 
standard Weather Bureau stations in the areas affected. Thus it is now often 
possible to save thousands of dollars by discontinuing projects in bark-beetle 
control, already started or planned, when it is known that temperatures low 
enough to bo fatal have occurred in the area. It is also known that the reduc- 
tion in numbers is only a very temporary one if other natural factors remain 
favorable to the insects. 
IMPROVEMENT OF BARK PEETI K CONTROL METHODS 
The problem of how bark beetles can be controlled by the introduction of 
chemicals into the sap stream of recently Infested trees seems to ho approach- 
ing a practical solution. When the proper chemicals are used this method 
has the added advantage of preserving the wood until it can be utilized. Last 
season's work along this line was especially promising. More favorable results 
than heretofore were also obtained with a lethal oil which, when Sprayed upon 
infested bark, will penetrate sufficiently to kill the bark beetle brood within. 
This spray has proved much more efficient on thin-barked lodgepole pine than 
on ponderosa pine. The earlier results on the thicker-barked sugar pine and 
ponderosa pine, although promising, were rather erratic. The development o\~ 
such a method n\ i 1 1 reduce control costs materially and at the same time will 
eliminate the danger from tire associated with the control methods qow in use. 
INVESTIGATIONS in EASTERN STATES 
III the East the projects on white gTUDS in nurseries and plantations, the lOCUSl 
borer, the White-pine weevil, the southern pine beetle, and various other native 
and Introduced foresl Insects have been continued. An extensive survey of the 
Infestation by the recently Introduced European spruce Bawfly has shown that 
it i- generally distributed throughout New England and New fork as far west 
Rochester. At no place, however, has a heavy infestation been found in 
this country. Several generations occur annually in southern New England, 
while in northern Maine one Is apparently the rule. 
Experiments toward development of a technique for controlling defoliating 
inserts in forested areas l.y releasing poisons from an autOgirO have 
encouraging results. The poisons have been applied in the form t^\' concentrated 
mixtures of lead arsenate, calcium arsenate, or derriS in water, with lish oil ;is 
an adhesive. 
\ . I DOBS of I 111 Ml 1< It 1 I M IMS! 
During the year work on known and possible rectors ^f the Dutch elm d: 
has been greatly Increased, in this work, now located at Blorristown, v .1 . 
many cases of transmission have been obtained by the normal reeding of the 
smaller European elm bark beetle {Scolytu* multittriatm Marsh.) upon pre- 
viously healthy young elm-. The aative elm bark beetle [Hylurgopimm* nt/lpsv 
Kiel 1 1 1. 1 has also been shown to u a bearer ^\' the disease, and numerous gn en, 
