CORNELL UNIVERSITY EXPERIMENT STATION BULLETINS. 257 



late as it is safe to do so is usually secure from the attacks of the fall 

 brood of the Hessian fly, Cecidomyia destructor. By harvesting the first 

 crop of clover for hay early in June, the bulk of the first brood of the 

 clover-seed midge, Cecidomyia leguminicola, will be destroyed and the 

 second crop of seed be thus saved. Fall plowing destroys many ciit- worms 

 and the tender pupse and adults of wireworms which are hibernating. 

 Many similar instances might be given where a knowledge of the habits 

 of injurious insects have been of incalculable value to the fruitgrowers and 

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

 of insects, fruitgrowers and farmers would not now be so successfully 

 fighting many of their insect foes. 



Of the life history of the pear psylla but little has been recorded either 

 in Europe or in this country, although the insect has been known here as 

 a pest for nearly sixty years. As the attention of this department of the 

 station was first called to this pest at the beginning of winter, our study 

 of its life history naturally began with 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, 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 in this country have doubted that the adults of 

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

 winter is passed 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 and English observers. 



An examination of Mr. H. S Wright's orchard in December, 1891, 

 revealed a hibernating brood of adults. Notwithstanding the great num- 

 bers 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 fgrmed 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 num- 

 bers, and an examination of the females in December showed no mature 

 eggs. The trees were examined several times during the winter; the adults 

 remained in their hiding places, and none were seen in copulation, nor 

 were any eggs seen before April 7, 1892. It was thus evident that Psylla 

 pyricola does not pass the winter in the egg state, but that there is a hiber- 

 nating brood of adults whose eggs are not laid until spring. 



Oviposifion of the ivinter brood. — -A few days of warm spring weather 

 occurred about April 7, 1892, and many of the hibernating adults were 

 seen in copulation, and a few eggs were also laid. Spring then opened 

 and by April 18 a majority of the eggs had been deposited. The eggs were 

 placed in the creases of the bark, or in old leaf scars about the basis of the 



terminal buds of the preceding year's giowth; some 

 were seen about the side buds near the terminal ones. 

 They were usually laid singly but rows of eight or ten 

 Fig. 4. -Egg. were sometimes found. The eggs (Fig. 4} are scarcely 



visible to the unaided eye; it would take eighty of them placed end to end 

 •AS 



