430 Report of the Department of Entomology of the 



autumn of 1913, owing to unusually mild temperatures, and in 

 that year comparatively few " flies " sought protection from the 

 cold before the last days of December. 



While the weather was permanently cold during these months 

 the adults remained secluded. In 1910 and 1911 a warm period 

 of several days' duration occurred during the last week of November 

 of each year at which time the unusual warmth during the sunny 

 hours of each day caused myriads of " flies " to leave their hiding 

 places and gather on the bud spurs and tender growth in the center 

 of the trees where they remained although the temperatures at 

 night in the most instances were quite low. 



In preparing the tables, the influence of winds, rains and cold 

 storms was not considered, but these factors undoubtedly have 

 obscured the effects of temperature to a considerable extent during 

 some years. It appears from these records that some " flies " after 

 they have once hibernated became active again during the fall or 

 early winter at a mean temperature as low as 32° F., under some 

 conditions, but even at that temperature there was very little 

 activity if colder days had recently occurred. A mean temperature 

 in the fall of about 42° F. usually caused myriads of the "flies" 

 to appear in exposed positions on the trees. Beneath the bark, 

 movement on the part of the insects sometimes was observed at 

 lower temperatures than those indicated in Tables II and III. 

 After the " flies " emerged from shelter they remained semi-dormant 

 on the trees at temperatures less than those at which they emerged 

 from hiding quarters, but it appears from our studies that a mean 

 temperature of at least 40° F., is required to cause the "flies" to 

 leave their shelter during the fall or winter months. 



In the spring the susceptibilities of adult psyllas to slight increases 

 in temperature resulted in extensive movements of the insects, 

 very early each season, from their winter quarters to the limbs and 

 smaller branches of the trees. At this period the trees were dormant 

 and the development of the buds had not commenced. Under such 

 conditions the " flies " chose by preference the newer succulent 

 growth within the center of the trees, and the blossom bud spurs 

 about the lower branches. Within a few days, if warmth continued, 

 the " flies " scattered over the trees and disseminated through the 

 orchards. In March, 1910, adults began to jump and fly two days 

 after leaving their hiding places, but during 1911 these activities 



