MONTANA EXPERIMENT STATION. 145 



sented by the feeding- grounds; the caterpillars often continue their 

 activity until llu' ni(irnin>;- is well advanced. They attain to a lenj^th 

 (.)f between 8 and lo nnu. before retirinj^ for the sec(Mid sherklin^ of 

 the skin. It became evident then that this ])eri()d would be especial- 

 ly favorable for the first experiment in spraying-. Accordin^c^ly, on 

 May 25th a limb of the tree containino;- 90 hibernacula by actual 

 count was g'ixcn a thorou^ih coat of .\rsenate of Lead in al)ont the 

 proportion of 5 pounds to 50 "gallons of water. .V tarred band was 

 placed about the base of the limb to prevent mi<^ration to other 

 parts of the tree and the ground l)eneath was covered l)y a sheet 

 to ascertain whether or not the worms would drop to the ground, 

 either as a means of escape or when overcome by the poison. After 

 about two days it was evident that they were not pursuing their 

 usual habits. Late in the day there were a nund^er moving about 

 on the leaves as though still in search of desirable food ; many of 

 these were on the under side of the leaves which were not so heavily 

 coated with poison. They did not feed here, however, and e\'en the 

 customary haunts did not show signs of having been visited. The 

 worms did not grow and soon began to show the effects of their 

 abstinence ; some very evidently died of poison and others shrivelled 

 and died in the cocoons. About a fourth of the cocoons were 

 empty and a small per cent of the larvae were found to drop to the 

 sheet, these however were entirely those suft'ering from poison so 

 that they were unable to attach their threads to the leaves. 



Many ants, beetles and spiders were running al)out over the sheet 

 ?nd some were even seen carrying larvae away. .\n estimate of 

 75 per cent was recorded in the notes for the insects destroyed by 

 this spraying, and there was no appreciable damage done to the 

 foliage l)y the insects after it was applied. A final examination' 

 was made after pupation had begun and it was found that only a 

 single worm had attained to the pupa stage. 



Pupation began June 7th and by the loth about a third of the in- 

 sects were in this stage. It was often undertaken in the last hi- 

 bernacula but it was especially noticeable that as many as half of 

 the worms constructed new cocoons. These were almost entirely 

 the product of the spinnerets, were constructed in the same way and 

 attached in the same places as the winter hibernacula. Often the 

 old winter quarters themselves were reconstructed and utilized for 



