THE AIRPLANE IN CATALPA SPHINX CONTROL 133 



dust can be fairly estimated. After this is done a "trial puff" of 

 the powder can be made and the "range" secured. Using the trial 

 puff as a basis for correction the actual work of dusting can be be- 

 gun with a fair degree of confidence that the cloud will settle where 

 desired. 



THE EFFECT ON THE CATERPILLARS 



The morning following the application of the dust some dead 

 caterpillars were to be found in the grove and many were ailing. 

 Forty-six hours after the poison was applied evidence of the whole- 

 sale slaughter of the insects was apparent on every hand. Every 

 part of the grove was literally polluted by the dead and dying lar- 

 vae. Their bodies were hanging in every conceivable position on 

 the trunks, branches, and foliage of the trees, fence posts, and 

 weeds; and they were lying in the greatest profusion xm the refuse 

 of the forest floor ; while still others had sought seclusion beneath 

 fallen leaves, twigs, etc. Not a single step could be taken without 

 crushing numbers of them. 



The large as well as the small caterpillars were killed. Pre- 

 vious to the test it was feared that the full grown horn-worms 

 might be able to withstand the treatment, since it is well known 

 that the large horn- worms are rather difficult to kill. 



The most careful and painstaking observations indicated that 

 the poison had destroyed at least 99 percent of the caterpillars 

 present at the time of its application. Unfortunately, however, as 

 indicated previously, some individuals of the caterpillar brood had 

 already passed into the soil and pupated when the work of dusting 

 was done. These formed the basis for a third brood of worms 

 which appeared in September and again defoliated the grove. 



The effect on the trees of the two complete defoliations in June 

 and September and the 75 percent defoliation of July coupled with 

 the rigors of an abnormally dry summer proved fatal to many trees 

 and the grove is being cut for market at this time. Had it been 

 possible to have made the application of dusting a week earlier, 

 much of the second crop of foliage would have been preserved and 

 it seems reasonable to believe that the numbers of the third brood 

 of caterpillars would have been greatly lessened. The writer con- 

 fidently believes that if it had been possible to give the trees this 

 bit of assistance they would have emerged from their experience 

 with the caterpillars with sufficient vitality to leaf out this spring 

 and continue growing. 



