436 Report of the Department of Entomology of the 



Table VIII. — Incubation Period of First Brood Eggs of Pear Pstlla under 



Artificial Conditions. 



Lot No. 



I. . 

 II.. 

 III. 

 IV. 



v.. 



VI. 

 VII 



Number 

 of eggs. 



207 

 44 

 100 

 100 

 64 

 45 

 38 



Date of 

 deposition. 



Mar. 30 



April 1 



April 6 



April 8 



April 13 



April 15 



April 12 



Date of 

 hatching. 



April 10 



April 11 



April 18 



April 19 



April 23 



April 25 



April 19 



Period of 

 incubation. 



12 days 



12 days 



13 days 

 11 days 

 11 days 

 11 days 



8 days 



The indoor temperatures in these tests were very favorable for 

 early hatching of the eggs. Out of doors in New York the normal 

 temperatures during April are apt to be low and consequently the 

 incubation period of psylla eggs is usually longer. According to 

 Slingerland's 12 observations eggs, of this species deposited on April 7 

 hatched on May 10. At Geneva some records were obtained on 

 the duration of the egg stage in 1911 under natural conditions which 

 are given in the accompanying table. 



Table IX. — Hatching of First Brood Psylla Eggs under Natural Conditions 



During 1910. 



Lot No. 



Period of 

 incubation. 



I.. 

 II. 

 Ill 

 IV 



V. 



18 days 

 18 days 

 18 days 

 15 days 

 12 days 



From this table it would appear that about eighteen days was 

 the usual incubation period for eggs deposited during the early 

 days of April, 1910, but the time required for the development of 

 the ova became less as the warm days of May approached. In 

 our observations over several years we have noticed that normally 

 psylla eggs hatch in about three weeks but this period is some- 



"Cornell Univ. Expt. Sta. Bui. 44:168. 1892. 



