The Pear Tkee Pstlla. 235 



rious insects have been of incalculable value to the fruit growers 

 and farmers. In fact, were it not for such, observations upon the 

 life histories of insects, fruit growers and farmers would not now 

 be so successfully fighting manj^ of their insect foes. 



Of the life history of the Pear Psylla but little has been recorded 

 either in Eurox>e or in this country, although the insect has been 

 known here as a pest for nearly sixty years. As the attention of 

 this depar-tnient of the station was first called to this pest at the 

 beginning of winter, our study of its life history naturally began 

 witli the stage in which the insect was then hibernating. 



Hibernation. — Observers have differed in their statements in 

 regard to the stage in which this insect passes the winter. Dr. 

 Franz Low, speaking of the three Pear Psyllids (Terh. der Zool. 

 Bot-Ges. in Wien, 1886, p. 154) sums up the general European 

 opinion on this point in saying that the adults hibernate and lay 

 their eggs in the spring ; not in the fall and spring as translated in 

 Insect Life, IV, 127. Barnard, Thomas and Ashmead (see bibliog- 

 raph}- for references) in this country have doubted that the adults 

 of Psylla pyricola wait until spring to lay their eggs. Dr. Lintner 

 (Countiy Gentleman, August G, 1891) says the winter 'is pasised 

 in the egg state. Some species of Psylla, as P. mali, appear to 

 pass the winter in the egg state according to the observations of 

 Schmidberger (KoUar's Treatise, p. 278) and English observers 

 (Miss Onnerod's fourteenth report, p. 4, 1891). 



An examiaation of INIr. H. S. Wright's orchard in December, 

 1891, revealed a hibernating brood of adults. Notwithstanding 

 the great numbers in which the insect had appeared during the 

 summer, comparatively few of these adults could be found. Most 

 of them were hidden in the crevices under the loosened bark on 

 the trunk and large limbs of the tree; a favorite hiding place on 

 some trees was in the cavity formed by the bark growing about 

 the scar of a severed limb ; on account of its being quite warm at 

 the time, some adults were crawling about on the branches. The 

 adults were not easily seen as they were so minute and their color 

 so closely imitated the bark of the tree. Both sexes were found in 

 about equal nmnbers, and an examination of the females in 

 December showed no mature eggs. The trees were ex an lined sev- 



