New York Agricultural Experiment Station. 427 



STUDIES OF THE HABITS AND OVIPOSITION OF 

 HIBERNATING "FLIES." 



time of transformation of hibernating adults. 



The abundance of psyllas during the years 1909-1913 afforded 

 ample opportunity to watch the activities of the hibernating brood of 

 this insect. Transformation to winter adults occurred in late Septem- 

 ber or October of each year as shown in the accompanying table. 



Table I. — Time of Transformation of Psylla Adults in the Fall. 



First appearance of "flies" of winter brood 



Average greatest abundance 



Latest appearance of nymphs of summer 

 brood 



1913. 



Sept. 29 

 Oct. 20 



Oct. 30 



CONDITIONS UNDER WHICH " FLIES " HIBERNATE. 



Pear trees of all varieties were equally sought by the adults as 

 food, and sheltered the largest number of these insects. Other 

 kinds of fruits on which hibernating psylla " flies " were often 

 observed were apple, cherry, peach and plum, but the infestation 

 of these fruits was apparently due to their nearness to infested 

 pear plantings. Many adults were also found each year under 

 leaves or other rubbish, and in tufts of grass. In 1912 large numbers 

 of them collected about the " collar " and in some instances in 

 fissures in the soil near the trunks of the trees. Other objects 

 such as fence posts and out-buildings were sometimes found to harbor 

 the " flies " which presumably had crawled to them after having 

 been blown from the trees or having become numbed from the 

 cold and dropped to the ground. 



RELATION OF TEMPERATURE TO THE ACTIVITIES OF HIBERNATING 



" FLIES " IN THE FALL. 



The movement of " flies " to winter quarters during the years 

 1910-1912, of which data are shown in Tables II and III, began 

 with the continued freezing temperatures of October and November. 

 As indicated in Table III this movement was less marked during the 



