INSECT PESTS OP OHIO SHADE AND FOREST TREES 223 



silken threads, and it has been long and well known that the larvae 

 would lower themselves by the spun thread if the tree or branch 

 was sharply jarred. However, it was not until recently that W. H. 

 Goodwin (See Monthly Bui. Ohio Agricultural Experiment Station 

 March, 1918), observed that the very tiny larvae have the habit of 

 spinning out a length of thread, letting all holds go and sailing away 

 in the breeze. At the end of the second day's feeding, however, 

 their bouyancy is so decreased that they are no longer able to float. 

 Some larvae were observed by Goodwin to float as far as 25 rods. 



The observations of Goodwin pertaining to the floating habit 

 of the larvae have done much to clear up the mystery of the spread 

 of the insect. Because of the wingless state of the female, spread 

 cannot be effected through the agency of adult flight, nor is it pos- 

 sible through the movement of egg masses ; nevertheless, in actual 

 field conditions the spread sometimes is appalingly rapid, and in the 

 drifting of the larvae lies by all odds the most logical explanation. 

 At the same time these observations have done much to alter con- 

 trol recommendations as will be pointed out later. 



From 4 to 6 weeks' time is occupied in larval growth, and at the 

 end of this period the worms descend to the earth, enter to a depth 

 of from 1 to 4 inches and pass to the pupal stage. 



From this point the life history of the two species is quite 

 different. The spring cankerworm, so far as is known, invariably 

 remains in the soil until the following spring, but under some con- 

 ditions the adults of the fall species may emerge in late fall, though 

 in Ohio it seems that most emerge in late winter or very early 

 spring. Weather conditions have much to do with the exact time 

 of emergence. According to Goodwin's observations, 5 to 8 succes- 

 sive days of temperature above freezing at night and in the neigh- 

 borhood of 50 F. during the day, usually will bring out the brood. 

 The entire brood, however, does not appear at once, but the spring 

 emergence may extend over a period of 6 weeks or more. 



Because of the wingless condition of the females they crawl up 

 the trunk of the tree, most of them preferring to make the journey 

 during the early hours of darkness. As the females ascend, the 

 males visit and fertilize them, adn egg deposition by the fall species, 

 takes place for the most part on the twigs high up in the top of the 

 tree but the spring species oviposits lower down on the trunk and 

 limbs of the host, tucking the eggs away in tiny clusters beneath 

 the flaky bark scales. 



