32 SOME INSECTS INJURIOUS TO FORESTS. 



increasing in size and very active, so that by May 20 some of them 

 were more than half grown. They continued actively feeding and 

 growing until after the middle of July, when the} T began to trans- 

 form to pupa? and continued transforming during August until all had 

 transformed, probably by the 1st of September. The pupae begin 

 transforming to adults about the 1st of August and continue trans- 

 forming probably into September, although the principal transforma- 

 tion is in August. 



ACTIVITY OF THE ADULTS. 



The adults begin to emerge as early as the 7th of August, and con- 

 tinue emerging until the last of September, the greater number com- 

 ing out during the last part of August and the first half of September. 

 Evidently all beetles are out by the first week in October. 



The females begin to deposit eggs within a few hours after they 

 emerge. The principal period of oviposition appears to be between 

 the middle of August and middle of September, but oviposition con- 

 tinues until in October. The eggs hatch within eight or ten days 

 after they are deposited, and the young larva? excavate their hiber- 

 nating cells and remain dormant until the following spring. 



VARIATION IX SEASONAL HISTORY BETWEEN DIFFERENT LATITUDES 



AND ALTITUDES. 



Phenological investigations of plants and insects by the writer a 

 during the past ten } T ears indicate that the average difference in the dates 

 of occurrence of the different stages of Cyllene robinidd at different 

 latitudes and altitudes in the eastern United States will not be far 

 from four days later for each degree north of latitude 39° and for 

 each 400 feet of altitude above Washington at the same latitude, or 

 four days earlier for each degree south of latitude 39° at the same 

 altitude. 



Thus, at latitude 43° in central New York, or central Michigan, with 

 altitude the same as at Washington, the dates would be about sixteen 

 days later, and at altitudes of 1,000 feet at latitude 43° they would be 

 about twenty-six days later; at the same altitude as that of Washing- 

 ton at latitude 35° in southern North Carolina and Tennessee they 

 would be about sixteen days earlier or at 1,600 feet elevation about 

 the same. Thus we would have about thirty-two days' difference 

 between localities at the same altitude in central New York and 

 southern North Carolina. We would also have thirty-two days' differ- 

 ence between Washington and localities at latitude 39° and altitudes 

 of 3,200 feet in the mountains of Virginia and West Virginia. 



a Bull. 50, W. Va. Agric. Exp. Sta., 1898, pp. 17, 18, and Bui. 67, 1900, pp. 241- 

 248, with map. 



