12 BULLETIN 805, U. S. DEPARTINIEXT OF AGRICULTURE. 



First Generation, 

 first brood of eggs. 



Lengtli of incubation period* — The adult females are very rarely 

 seen depositing eggs since they are very agile in their movements 

 and take flight at the slightest disturbance. Moreover, even though 

 a female is observed in the act of oviposition, the egg is seldom 

 detected, as it is inserted under the epidermis and is further hidden 

 by the downy pubescence of the leaf. For these reasons only approxi- 

 mate records of the length of the egg stage could be secured. 



Data on the incubation period were obtained by confining copu- 

 lating pairs of overwintered adults on a seedling tree in a globe cage. 

 The adults were removed after 24 hours and a daily record was kept 

 of the nymphs as they hatched. The length of the egg stage, together 

 with the average mean temperature for the entire period, is given in 

 Table III. The average incubation period was 7.5 to 9.5 days; 

 the maximum, 10 to 12 days; the minimum, 5 to 7 days. 



Table III. — Length of incubation period of first-brood eggs deposited by overicintered 

 females of the apple leaf hopper in confinement, West Chester, Pa., 1915. 



TWENTY PAIRS OF OVERWINTERED ADULTS PLACED ON APPLE TREE JUNE 13, 

 12 M.; ADULTS REMOVED JUNE 14, 12 M. 



1915, 



Date of removal of newly hatched nymphs. 



Number 



of 

 nymphs 

 removed. 



Length 

 of in- 

 cubation 

 period. 



Average 



tempera- 

 ture for 

 entire 

 period. 



1915. 

 June 20, 12 m 



2 

 47 



30 



10 



4 



1 



Days. 

 5-7 



6-8 



7-9 



8 -10 



9 -11 



10 -12 



79.56 



June 21, 12 m 



78.61 



June 22, 12 m 



77.00 



June 23, 12 m. 



75.90 



June 24, 12 m 



75.20 



June 25, 12 m 



75.07 











7. 5- 9. 5 76. 89 











FIRST BROOD OF NYMPHS. 



Length of stages. — The length of the nymphal stages and of the 

 entire nymphal period was obtained by conhning newly hatched 

 nymphs in the cork cages described on page 8. Each cage was 

 examined daily and a record made of the length of each stage, the 

 cast skins being removed from the cages after each molt. The 

 length of each stage and of the entire nymphal period is shown in 

 Table IV; the average mean temperature for each nymphal period 

 is also included. The average length of the nymphal period for 

 22 nymphs was 18.7 days; the maximum, 22 days; the minimum, 

 15 days. 



