10 



BULLETIN 438, U. S. DEPARTMENT OF AGEICULTURE. 



THE EGG. 



In California, in Santa Clara Comity, in 1912, eggs were first ob- 

 served on trees as early as March 23, and in Contra Costa County, in 

 1913, as early as Marcli 25. During the last few days of March in 

 both these years oviposition was observed. In Washington, in 1915, 

 numerous females were observed in the Zimmerman orchard on April 

 7, though none had been found 3 days before. None was seen to ovi- 

 posit on this date, and they were evidently all very recently emerged. 

 A week later the period of oviposition was at its height and by April 

 24 most of the adults had disappeared. The adults prefer to ovi- 

 posit on those varieties of pears which leaf out early and generally 

 select for oviposition a young leaf not yet unrolled. In California 

 the earhest adults generally find the Bartlett not far enough advanced, 

 and so the earhest eggs are deposited on other varieties. Ovipositing 

 females kept in a jar were provided with cherry and plum leaves, but 

 they refused these as hosts, although, in similar confinement, they 

 oviposited regularly in pear leaves. 



Table II indicates the incubation period in California for 85 eggs : 



Table II. — Incubation record of eggs of the pear leaf-worm, Walnut CreeTc, Cal., 1913. 



Number 



Date of 

 deposi- 

 tion. 



Date of 



Number 



Incuba- 



posited. 



hatching. 



batched. 



tion stage. 











Days. 



118 



Mar. 29 



Apr. 7 



23 



9 







Apr. 8 



6 



10 







Apr. 9 



21 



11 







Apr. 10 



£8 



12 







Apr. 11 



5 



13 







Apr. 12 



2 



14 



For this experiment 20 adults were confined in a cage in which a 

 growing pear limb was inclosed. The average incubation stage was 

 11.1 days. Out of 118 eggs deposited, 85, or 72 per cent, hatched. 



Table III indicates the incubation period, in Washington, of 23 eggs 

 deposited by a single unfertilized female on a pear twig kept in water. 



Table III. — Incubation record of eggs of the pear leaf-worm, Wenatchee, Wash., 1915. 



Number 

 of eggs 

 depos- 

 ited. 



Date of 

 deposi- 

 tion. 



Date of 

 hatching. 



Number 

 hatched. 



47 



Apr. 11-14 



Apr. 19 

 Apr. 20 

 Apr. 21 

 Apr. 22 

 Apr. 23 

 Apr. 24 



10 

 4 

 1 

 1 

 

 1 



