226 



with equal rapacity upon this insect. From this particular species we 

 have reared no parasites, but in general the Aleyrodidse are quite sub- 

 feet to the attacks of Hyinenopterous parasites peculiar to them. We 

 have reared several species of these parasites from other species of this 

 tamily in this country, but we will leave their characterization and con- 

 sideration to a future article, in which we hope at the same time to de- 

 scribe several species of the family AleyrodidiTe found commonly upon 

 different trees in the United States. 



Fig. 25.— Psylla pyricola: full-grown 

 uympli, dorsal view— enlarged (after 

 Slingerlaud). 



THE PEAR-TREE PSYLLA. 



As an elaboraticm of the short paper published in No. 2 of the cur- 

 rent volume of Insect Life, and first read before the Association of 

 Economic Entomologists at Eochester, 

 Mr. Slingerland gives the results of his 

 observations upon this important ])ear 

 tree pest in one of the most creditable 

 and useful of the station bulletins* 



PsyJla injHcola is an old oftender and 

 its natural history has been repeatedly 

 treated both in Europe and America, but 

 n.ever before so thoroughly as has been 

 done by Mr. Slingerland. It appears from 

 his careful observations, made in 1892, 

 that the hibernating imagos emerge from 

 their winter retreats on the first warm 

 days of spring, copulate, and commence 

 to lay eggs about the middle of April. The eggs hatched about four 

 weeks later, and the imagos of this first summer generation appeared 

 from June 10 to June 15. The cycle of the second generation was 

 completed about one month afterwards, that of a third generation also 

 one month after the second (about August 20), and the 

 imagos of a fourth generation, which issued toward 

 the end of September, lived throughout the winter. 

 The development of the second generation Avas 

 carefully followed out with the following result : 

 Diiratiou of egg state from 8 to 10 days. 



First larval stage : duratiou six or seven days. Larva 0.013 

 iuch in lengtli, antenna; 3-jointed; wing-pads not visible; 

 general color pale translucent yellow, witlioiit luarkiugs; ab- 

 domen more opaque and darker. 



Second larval stage: duration about four days. Larva one- 

 third larger than first stage, but of same color, except tliat the 

 tii)s of autennie are black. Antenme 4-jofnted; segments of 

 abdomen more distinct, and wing-pads developing. 

 Third larval stage : duration about three days. Larva 0.027 iuch in length; black 



cola: adult— 



(after Slingerland). 



* Bulletin 44, Cornell University Agricultural Experiment Station, Entomological 

 Division. Ithaca, N. Y., October, 1892. 



