INSECT ENEMIES OF EASTERN FORESTS 13 
some areas practically all the mature hemlocks have since died. The 
hemlock borer increased enormously in numbers and attacked prac- 
tically all these dying trees, which called forth many inquiries as to 
the importance of this beetle. The hemlock stands on the Menominee 
Indian Reservation, Wis., likewise suffered in the drought period of 
1930 to 1937 in that region. The drought, combined with « overmaturity 
of the hemlock, death of the root systems, Armillaria root rot, and 
windthrow, made conditions ideal for an outstanding increase in the 
abundance of the hemlock borer. By 1938 the estimated mortality due 
to all these factors exceeded 100 million board feet on this reservation 
alone (Secrest, Lorenz, and Mac Aloney, 376). 
Extensive outbreaks of the southern pine beetle and hickory bark 
beetle have always occurred in drought years—1890-92, 1910-11, 
1922-24, 1930-33, and 1936-39, for example. Local outbreaks coincide 
with local deficiencies of precipitation for the summer months; in fact, 
this is so invariably the case that of recent years it has been ‘possible 
to predict local outbreaks on the basis of deficiencies in rainfall. This 
relationship between drought and insect attack has been treated by 
Blackman (39), St. George (367, 369), Craighead (177), and Wygant 
(437). 
Oaks are also affected by drought, but the association of insect attack 
is not so clear, often being delayed 2 or 3 years, by which time the 
trees show attack by a root rot (Armillaria), or readily become infested 
with Agrilus beetles, and die. 
Black locust is easily affected by drought, particularly a spring 
drought which permits development of a high percentage of the locust 
borer larvae in the phloem and consequent girdling and death of the 
tree (Craighead, 776). 
STORMS 
Severe beating rainstorms are known to have controlled outbreaks 
by knocking the young larvae of defoliators off the fohage of trees, 
or by drowning bark beetles during flight periods. Hailstorms, like 
rainstorms, beat insects off the foliage “of trees and effect a measure 
of control. The stones often bruise the upper side of branches, how- 
ever, causing lesions which become infiltrated with resin. This cuts 
off conduction and may sometime later cause the death of twigs on 
coniferous trees. 
Many bark- and wood-boring insects that are dependent on dead 
wood are kept well supplied with breeding material by broken 
branches, tops, or wind-thrown trees: and occasional tornadoes and 
hurricanes leave swaths of fallen timber. This material is quickly 
attacked by bark beetles and borers. Sometimes the bark beetles mul- 
tiplying in these logs attack and kill adjacent green timber. 
FIRE 
Fire-scorched or fire-killed trees have a marked attraction for 
certain insects, as they are especially favorable for the breeding of 
many species. Adults attracted into the area lay eggs in the dead 
and dying trees, and the insects increase enormously in ‘umbers. This 
attraction is so pronounced that every tree in suitable condition over 
the entire burn, often covering many square miles, may be attacked 
in a few weeks’ time. For the most part, insects attacking these trees 
