148 MONTANA EXPERIMENT STATION. 



' must be coated with poison before they were fastened together and 

 on July 15th, before a large per cent of the worms had begun to 

 fasten the leaves together, a part of the tree was given a thorough 

 spraying of arsenate of lead in nearly twice as strong a solution as 

 that formerly applied. Special attention was given to coating the 

 nnder side of the leaves. 



Il v\;is r.aturnlh- so'r-'^ time before the efifect of this spraying be- 

 came evident, smce il •■•.as not until about July 30th that the process 

 of fastening leaves together in the construction of the so-called 

 houses, Vi-hich has been so thoroughly discussed in previous publi- 

 cations, began to come into prominence on other parts of the tree. 

 It was now noticeable that these transformations were not going on 

 in the sprayed limbs. A careful examination of the larvae here 

 showed that while they were largely still active, bewteen 5 and 10 

 per cent only being found dead, yet their ravages had been confined 

 almost entirely to the leaves upon which they had hatched, and that 

 even here the feeding was far down tmder the coating of poison and 

 not extended as in other parts of the tree. On August 6th the 

 per cent of dead larvae on the sprayed limbs had increased consid- 

 erably and there was very little noticeable extending of the feeding 

 grounds. By August i8th the condition was still more aggravated, 

 and when on the 22nd a final examination was made the effect of the 

 poison was very evident. On unsprayed parts of the tree the 

 leaves were largely turning brown as a result of the ravages of the 

 worm and the '"Houses" consisted of from 2 to 5 leaves. The spray- 

 ed parts were practically free from clusters of leaves fastened toge- 

 ther, and the foliage was still fresh and green. Though a small 

 per cent of the worms were still alive they were not developing as 

 rapidly as the others and, judging from the observations taken at 

 the first spraying, would never live to go into winter quarters. 



The summer was unusually dry and only two heavy rains had 

 takn place since the first spraying on May 25th. That limb w^as 

 now, on August 22nd, by far the freshest on the tree and most free 

 from attack, ai.d still retained a considerable film of the Arsenate of 

 L. ad. 



While the experiments given above were limited in their applica- 

 tion they certainly show that the range of control of this pest is 

 much wider than was formerly supposed. The fact that the larva 



