PROTECTION FROM THE LOCUST BORER. 3 



Possible reasons for such iniinimity 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 tinpruned 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 thinl? 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 Pailroad right of ways were se- 

 lected and used as experimental plats. Some of these near Falls 

 Church were pruned while others were left as the}^ were found. The 

 history of plantations along the Pennsylvania Eailroad 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, 

 tulix3, 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 fovmd 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 b}^ the borer. 



2. Just across a road from the tract described above is an old 

 orchard which is used as a j)asture. About two dozen locusts of the 



