318 MISC. PUBLICATION 657, U. S. DEPT. OF AGRICULTURE 
The most striking fact regarding the southern pine beetie is the 
rapidity with which populations of the beetle both increase and de- 
crease, because of only slight variations from normal or average 
climatic conditions. Craighead (///) correlated the appearance of 
Incipient epidemics with deficiencies in rainfall. A drop of 1 inch 
or more below the normal monthly precipitation for several months 
is likely to be followed by a marked increase in infestation, which may 
or may not develop to epidemic proportions, depending on whether or 
not the moisture deficiency is continued. When an incipient outbreak 
seems well under way, a return to normal or excess rainfall is promptly 
followed by a marked reduction in beetle survival. This beetle is 
readily controlled by temperatures around zero Fahrenheit (p. 12). 
The following measures have been suggested to prevent serious 
outbreaks: Encourage a mixture of the “better hardwoods in pine 
stands. Prevent fires, as these weaken trees and attract bark beetles. 
Watch for infestations in decadent pines and in trees injured by 
lightning or windstorms. During drought periods watch for the 
first evidence of the southern pine beetles and treat the trees harbori ing 
them. 
Discussion of methods of controlling outbreaks of pine beetles will 
be found on pages 47-51. 
The eastern spruce beetle (Dendroctonus piceaperda) 1s con- 
siderably larger than the southern pine beetle, being usual!y be- 
tween 5 and 6 mm. long. The head, pronotum, and abdomen are 
black and the wing covers reddish brown. It is a native insect, found 
from central Pennsylvania northward through New York, northern 
New England, and the Maritime Provinces of Canada and New- 
foundland, and westward to Michigan and Manitoba. It attacks and 
kills the native red, white, and black spruces. 
Adults of the eastern spruce beetle are in flight at all times through- 
out the summer from June to September, but the heaviest attack 
occurs late in June and early in July. The seasonal history of the 
beetles is greatly complicated by the fact that the parent beetles after 
laying one complement of eggs, emerge from the first tree attacked 
by them, and enter and lay their eggs in a second tree. The beetles 
are monogamous, and the egg gallery consists of an unbranched, longi- 
tudinal burrow about 6 inches long, at the line of the inner bark and 
wood, but almost entirely in the former. The eggs are deposited 
in large groups in grooves along alternate sides of the ege gallery, 
where they are packed j in boring dust and walled off from the bore of 
the gallery. On hatching, the larvae from each ego group feed to- 
eether in a common chamber, but soon each begins an ) individual mine 
and these mines, at first subparallel, diverge more and more as the 
larvae grow and extend their burrows. 
In a heavy infestation the beetle attack may extend from the base 
up into the crown of a tree, but more often only the lowermost 30 
feet or so 1s affected, while the top of the tree is filled in with secondary 
forms. Swain (402) established by actual count that an 18-inch red 
spruce in eastern Canada contained 750 egg galleries, and he estimated 
the number of eggs deposited in this tree at more than 100,000. Signs 
of attack by the eastern spruce beetle are the presence of red boring 
dust and pitch tubes on the bark, the fading and dropping of the 
foliage, and the reddish appearance of the twigs after the needles 
