THE EELATIOX OF INSECTS TO SLASH DISPOSAL ^ 



The ordinary method of slash disposal, by burning, destroys only 

 the small, entomologically innocuous parts of the slash, and leaves the 

 parts most favorable for insect breeding. Any method of slash dis- 

 posal that will reduce the number of insects must take care of the 

 larger material. Even burning slash piled over stumps does not as 

 a rule sufficiently char the stump to prevent subsequent insect infesta- 

 tion. Thorough charring can be accomplished only by keeping the 

 fire close to the sides of the stump throughout the process of burning. 

 Thorough charring of stumps is too expensive to be practical. Bark- 

 ing is cheaper, but must be carried down to the mineral soil if satis- 

 factory results are to be expected. 



Unpublished results of experiments in Minnesota indicate that 

 heavy shade is unfavorable to most potentially injurious insect species. 

 In one experiment, piling the small parts of the slash over the stumps 

 very materially reduced the infestation. This experiment was on a 

 small scale and only about 20 stumps were used, but the results were 

 very clear cut. Pairs of stumps close together were selected; one 

 of each pair was covered with the smaller parts of the slash, the 

 other stump being left uncovered. The uncovered stumps were found 

 to contain an average of 40 mother tunnels of Bendroctonus valens 

 per stump, whereas the covered stumps averaged only 4 each. 



From the data at hand the writers are forced to conclude that slash 

 burning in the Lake States is unnecessary from the entomological 

 point of view. Covering the stumps and larger pieces of the slash 

 with the smaller pieces promises satisfactory results at a minimum 

 cost. 



WESTERN WHITE PINE IN THE NORTHERN ROCKY MOUNTAIN REGION 



The most serious insect enemy of the western white pine {Pinus 

 monticola) is the bark beetle Bendroctonus monticolae Hopk. This 

 species breeds successfully in cull logs from logging operations, and 

 also kills living trees. General observations by Evenden indicate 

 that during continuous logging operations the progeny of such beetles 

 as breed in the cull logs are absorbed in the new material made avail- 

 able, so that little damage results to standing trees. Because of the 

 value of this timber species very close utilization is practiced, and 

 ordinarily only a very small quantity of slash over 6 inches in diam- 

 eter is left in the woods. Occasionally, however, where a certain 

 quantity of such material is left in the woods at the close of a logging 

 operation, and no fresh material is provided, the insects which emerge 

 attack and kill standing trees in the vicinity, or seed trees left on the 

 area occupied by the slash. 



As these beetles do not breed in the sm.aller tops and limbs the 

 present methods of brush disposal by burning can have no possible 

 effect upon their number. And because of the close utilization of 

 the larger material other measures for preventing injury by insects 

 do not ordinarily appear to be justified. If, however, for any reason, 

 any quantity of large slash material is left in the woods and no fresh 

 material is provided to absorb the emerging broods, then as a pro- 

 tective measure the bark should be peeled from the infested cull logs 

 before the beetles emerge; otherwise some damage to standing trees 

 may result. 



Two smaller species of insects {Pityogenes carinulatus Lee. and P. 

 knecJiteli Sw.) breed in the smaller material from the tops. Occa- 

 sionally they breed in sufficient numbers to attack and kill small 



