PKOTECTION FROM THE LOCUST BORER. 3 
Possible reasons for such immunity in dense stands were discussed 
with Dr. A. D. Hopkins in several letters during May, 1910. In a 
letter of May 11 Dr. Hopkins wrote : 
Perhaps with the unpruned trees there is more shade and, since the beetles 
are sun-loving and active during the day, the more open and light conditions 
found in the pruned groves may serve as the attractive influence. This is the 
only thing I can think of that would make the difference. Observations should 
be made during the period of flight to determine the relative number of beetles 
found on trees under shaded and sunny exposures. 
If this should lead to a solution of the problem and shaded conditions are 
favorable, then mixed planting with some quick growing tree like catalpa might 
be advisable. 
This seems a very plausible theory to account for the immunity of 
unpruned and natural growths, and it is substantiated in the experi- 
ments conducted. No other factors considered seem to cover the con- 
ditions in the many localities where trees were examined. 
INVESTIGATIONS AND EXPERIMENTS. 
Natural growths of locust in the vicinity of Falls Church, Va., and 
plantations along the Pennsylvania Railroad right of ways were se- 
lected and used as experimental plats. Some of these near Falls 
Church were pruned while others were left as they were found. The 
history of plantations along the Pennsylvania Railroad as to plant- 
ing and subsequent management has been furnished ,by the office 
of the forester of the railroad, which also provided facilities for the 
study of these plantations. 
NATURAL GROWTH IN THE VICINITY OF FALLS CHURCH, VA. 
1. On Miners Hill there is a stand of mixed growth of reproduction 
averaging 3 to 5 inches in diameter. The aspect is a westerly slope, 
the trees extending from the crest more than half way down the hill. 
It contains about an acre and is composed chiefly of oak, chestnut, 
tulip, persimmon, hickory, sassafras, maple, and locust. It is thickly 
undergrown with weeds and briers which now are dying out. The 
locust composed about 5 per cent of the stand. In the fall of 1915 
these locusts were from 2 to 3 inches in diameter and contained no 
borers. In January, 1916, one end of this plot, constituting about 
one-tenth of the area, was pruned; all trees, except the locust, were 
cut out. The following fall adult beetles were observed ovipositing 
on the trees thus isolated, and examination in the spring of 1917 
showed from 3 to 10 borers in each tree. Again in 1918 these trees 
were found to be heavily infested. In the remainder of the stand 
(that which is still growing naturally) about 1 tree in 10 can be 
found containing one or rarely two defects made by the borer. 
2. Just across a road from the tract described above is an old 
orchard which is used as a pasture. About two dozen locusts of the 
