:W0 LEAFHOPPERS INJURIOUS TO APPLE NURSERY STOCK. 



19 



The foregoing experiments indicate that third-brood adidts of the 

 apple leafhopper, under Pennsylvania conditions, do not deposit 

 winter eggs, but merely feed on the foliage until the time arrives for 

 them to seek shelter for the winter. 



The daily temperature for the period of seasonal activity is given 

 in Table XIII. 



SUMMARY OF SEASONAL HISTORY. 



The apple leafhopper passes the winter in the adult stage under 

 rubbish in the nursery or more often under accumulations of leaves 

 in adjoining woodlands. In the spring the overwintered adults 

 make their appearance on the trees during the latter part of May 

 and they feed on the underside of the terminal leaves for about 10 

 days before mating. The females deposit their eggs in the veins of 

 the terminal leaves, the average length of the incubation period of 

 the first-brood eggs being approximately one week. The feeding 

 period of this brood of nymphs extends from May 30 until about 

 the middle of July, the nymphs being most abundant during the 

 third week in June. The length of the first-brood nymphal period 

 varies from 15 to 22 days, the average being 18.7 days. First-brood 

 adults continue to emerge from June 20 to July 20. (See fig. 2.) 



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Fig. 2.— Seasonal history of the apple leafhopper at West Chester, Pa., 1915. 



Second-brood eggs hatch from the latter part of June until about 

 August 1, the length of the incubation period being about one week. 

 The second-brood nymphs commence to appear about the last part 

 of June, the larger percentage having developed into adults by the 

 middle of August. The average length of the second nymphal period 

 is 15.8 days; the maximum and minimum, 17 and 15 days, respect- 

 ively. Second-brood adults appear on the trees from the middle of 

 July until about a month later. 



