2 BULLETIN 787,, U. S. DEPARTMENT OF AGRICULTURE. 
the borer and grown profitably on a commercial scale if the locusts 
are planted in thick stands or mixed with other trees so as to produce 
a densely shaded condition and natural pruning during the first 10 
to 15 years of growth. 
HISTORICAL. 
The great variation in the extent of injury by borers to both 
planted and natural stands of black locust has been noted by many 
writers. In fact, as early as 1821, Pickering (2) 1 stated that trees 
of natural growth in groves were much less liable to injury than were 
transplanted trees. Schwarz (3) in 1890 observed that the insect 
lives in large colonies affecting all trees of small groves, while long 
hillsides full of locust are not infested. Cotton (5) observed that in 
Ohio injury was greater in single trees and plantations of consider- 
able size than in natural forests. Hopkins (6) remarked that " Favor- 
able conditions for the destructive work of the borer appear to be 
found in the presence of isolated trees and groves in the open. . . . 
Unfavorable conditions are found in forest growth or large areas of 
pure stands, or mixed stands where the locust predominates ; also, in 
plantations and groves where resistant varieties prevail, and where 
there is no goldenrod or other favorite food for the beetles." Dear- 
born (1), Kellogg (4). and Garman (T) also call attention to this 
fact. 
OBSERVATIONS BY THE WRITER. 
In examining locust plantations during the last few years, the 
writer was greatly impressed with the absolute destruction of some 
tracts, while others, or parts of the same tracts, were thrifty and un- 
marred by borers. This was convincing evidence that the trees 
could be grown so as not to be injured by the locust borer. Many 
tracts, therefore, both planted and natural, were studied with the 
idea of securing evidence that might be applicable in a practical 
way. As far as possible the accurate history of many locust stands, 
both pure and mixed, was obtained and factors that might be respon- 
sible for the presence or absence of injury were weighed. As a re- 
sult of such study, it was found that the amount of destruction was 
unquestionably greater in those tracts which had been pruned oc- 
casionally, closely grazed, or in which fire had gone through from 
time to time, killing out the underbrush and destroying the natural 
shade produced by weeds or shrubbery. The denser the growth, par- 
ticularly weeds and undergrowth about the stem of the tree, the 
less was the amount of borer work and vice versa. Pure stands in 
open fields, where the trees were growing from 2 to 3 feet apart, were 
seldom injured, while near-by isolated trees were riddled by the borer. 
1 Reference is made by number in parenthesis to " Literature cited," p. 12. 
