New York Agricultural Experiment Station. 437 



what extended if cold days prevail soon after deposition takes place. 

 On the other hand warm weather seems to hasten the development 

 of the eggs. The retardation and acceleration of the incubation 

 period because of weather conditions perhaps explains the almost 

 simultaneous hatching of psylla eggs which we have observed in 

 orchards in western New York during April or May of the years 

 1911 to 1913. The records during these years are as follows: 1910, 

 April 19; 1911, May 2; 1912, May 4; 1913, April 10. 



INFLUENCES OF NATURAL AGENCIES ON NUMBERS OF HIBERNATING 



" FLIES " AND THEIR EGGS. 



Fungus disease. — During the spring of 1911, small numbers of 

 the hibernating brood of psylla " flies " died soon after emergence. 

 Dead and inactive adults from orchards in Niagara county showed 

 upon examination the presence of a parasitic fungus, Empusa sp. 

 Collections of the " flies " taken at random from the trees showed 

 that about 2.5 per ct. of them were affected by the disease. Casual 

 observations have indicated that the fungus normally has but little 

 influence on the numbers of the psylla. 



Egg parasites. — A number of breedings have been made to 

 determine if the eggs of this insect are subject to parasitism, but our 

 studies so far have failed to find evidence of an egg parasite. It 

 would appear that parasites of psylla eggs, if they occur, are unimpor- 

 tant and these observations are included chiefly as a matter of record. 



Infertility of eggs. — Numerical counts were made to determine the 

 percentage of hatching of psylla eggs. The eggs used for this 

 purpose were those laid on the bud spurs and they were hatched 

 under natural conditions. The following figures show the number 

 of collapsed eggs as compared with fertile ones in these counts: 



Table X. — Showing Results of Counts as to Comparative Numbers of 



Fertile and Infertile Eggs. 



Sound eggs. Collapsed eggs. Infertile eggs. 



No. No. Per ct. 



2522 175 6.4 



685 65 9.0 



1628 123 9.8 



1000 80 7.4 



2763 225 7.6 



