SUSCEPTIBILITY TO SPRAYING MIXTURES OF 

 HIBERNATING PSYLLA ADULTS 

 AND THEIR EGGS.* 



H. E. HODGKISS. 



SUMMARY. 



Investigations of failures to control the psylla in pear orchards 

 led the Station to inquire into the susceptibilities of the hibernating 

 adults and their eggs to spray mixtures. 



Studies of the seasonal history and habits of the insect showed 

 that the pear psylla passes the winter as an adult or " fly," and 

 that it deposits its eggs in the spring within a short period after its 

 emergence from hibernating quarters. The psylla was observed 

 to winter over on various fruit trees such as apple, cherry, plum 

 and peach, but the largest number of the " flies " sought hiberna- 

 tion in the rough bark of pear trees. 



The behaviour of the hibernating "flies" in the fall was quite 

 different from the movements of the insects in the spring. During 

 a period in late fall or early winter when the weather moderated 

 it was observed that few of the " flies " remained in hiding and 

 that they largely clustered in the center of the trees. At such times 

 the adults walked but were sluggish in their movements and rarely 

 attempted to jump or fly. On the contrary, during the spring, as 

 a result of constantly increasing temperatures and the daily effective- 

 ness of sunlight, a few hours of time proved sufficient to induce 

 great activity among the adults. It was not uncommon for them 

 to jump or fly directly after emergence from their winter retreats. 



If moderate temperatures prevailed eggs were largely deposited 

 within a few days after the emergence of the hibernating adults 

 in the spring. Oviposition continued for several weeks, especially 

 if the weather was variable, but usually most of the eggs were 

 deposited before the last of April. Some ova were laid on foliage, 

 but it appeared that these normally are comparatively few in numbers 

 and result in little or no serious infestation of the foliage. 



* Reprint of Bulletin No. 387, May; for Popular Edition see p. 938. 



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