THE AIRPLANE IN CATALPA SPHINX CONTROL 



129 



4,815 in number, were planted twelve years ago for the growing of 

 post and pole timber. During that time growth had been satisfac- 

 tory, the trees having reached a height of from 25 to 30 feet and 

 averaging better than a post and a half per tree. 



CONDITION OF THE INSECT UNDER TREATMENT 



On June 30, 1921, when the writer first viewed the outbreak of 

 the catalpa sphinx in the Carver grove, the first brood of cater- 

 pillars was just reaching maturity and the trees were practically 

 devoid of foliage. During the 

 month of July the trees de- 

 veloped a second crop of foli- 

 age by the time the second 

 brood of caterpillars appeared. 

 The Engineering Division of 

 McCook Field made all pos- 

 sible haste to devise and man- 

 ufacture a poison distributor 

 and equip a plane with it, but 

 these arrangements were not 

 completed until August 2. By 

 that time the brood of worms 

 was about mature. Indeed, by 

 the following day when the 

 work was done, some had 

 passed to the soil and were in 

 the process of transforming to 

 the pupal stage. Thus these 

 were secure from the effects 

 of the poison treatment of the 

 foliage above. There remained 

 on the leaves, however, count- 

 less thousands of the larvae. 

 Had it been possible to do the 

 work just a few days sooner, 

 it doubtless would have made 

 a vast difference in the later 

 behavior of the trees. This 

 point will be considered more fully later on in the discussion. 



So plentiful were the numbers of this second brood of cater- 

 pillars that about 75 percent of the foliage had been destroyed by 



Fig. 8. The dark and light forms of 



the catalpa sphinx larva. 



Slightly enlarged 



