﻿THE GRAPE LEAPHOPPER IN THE LAKE ERIE VALLEY. 



27 



record made of the date of each molt. During this operation the 

 moisture was wiped from the inside of the watch glass. 



The period covered by these rearing experiments was from June 

 22 to October 13. During this time 348 newly hatched nymphs were 

 placed on grape leaves confined in cages similar to those just described. 

 Many of the nymphs either died or escaped before they completed 

 all of the nymphal stages. Nevertheless, complete records of the 

 length of the five stages were secured for 114 nymphs. The greater 

 number of fatalities occurred among the young nymphs during the 

 early part of the rearing season before the leaf cage most suitable for 

 the purpose was secured. After the double thickness of velvet was 

 adopted fewer fatalities occurred. 



The lengths of the several stages for the different individuals 

 show a great variation, but it will be noted by an examination of 

 Table XI that the variation of the total length of the five stages for 

 a number- of nymphs hatching on the same date is not very great. 

 Changes in temperature appear to be the important factor in deter- 

 mining the length of time required to complete the entire nymphal 

 period. 



In the last column of Table XI the average daily temperature 

 for the entire nymphal period of each of the 114 nymphs is given. 

 These average temperatures are computed from the average daily 

 temperatures given in Table XII. The average daily temperatures 

 given in Table XII are derived from daily readings of a maximum 

 and minimum thermometer, located in the garden of the laboratory 

 at North East, Pa., only a few yards distant from the grapevines 

 bearing the individual cages in which the nymphs were reared. 



Table XI. — Length of each of the five nymphal stages of the grape leaf hopper for 114 

 nymphs recorded from June 22 to October IS, 1912. 



si 

 1 























03 



a 

 ft 



v e r a g e daily 

 temperature for 

 entire nymphal 

 period. 



I 







jj 



© 









a) 







fl ■ 



ea 



A 











a 



CD 



SO 

 03 



4^ 







a 



•■a 







03 



-ti 

 a 

 



a 



-d 



.60 

 03 

 03 



d 



O 



a 

 a 

 3 



03 

 A 



a 



SO 



03 



A 



s.8 



, fH 



03 ft 



03 



.§ 



■U 







A 



A 







5 



W 







p 



f* 



h 



03 



m 



& 



H 



Ph 



fR 



fc 



h 



H 



< 



1912. 



1912. 



Dys. 



1912. 



Dys. 



1912. 



Dys. 



1912. 



Dys. 



1912. 



Dys. 



Dys. 



°F. 



June 22 



June 28 



6 



June 30 



2 



July 4 



4 



July 7 



3 



July 11 



4 



19 



74.90 



July 5 



July 9 



4 



July 10 



1 



July 13 



3 



July 16 



3 



July 25 



9 



20 



76.60 



July 9 



July 12 



3 



July 15 



3 



July 20 



5 



July 25 



S 



Aug. 8 



14 



30 



69.97 



Do... 



July 15 



6 



July 18 



3 



...do 



2 



...do 



5 



Aug. 7 



13 



29 



70.10 



Do... 



...do 



6 



July 17 

 July 15 



2 



July 21 

 July 20 



4 



July 28 

 Aug. 2 



7 



Aug. 8 

 Aug. 12 



11 



30 



69.97 



Do... 



July 12 



3 



3 



5 



13 



10 



34 



70.04 



Do... 



July 13 



4 



July 16 



3 



July 21 



5 



July 27 



6 



Aug. 9 



13 



31 



70.03 



Do... 



...do 



4 



July 17 

 do.... 



4 



July 19 

 July 21 

 July 19 



2 



July 25 



July 28 



do.... 



6 



Aug. 7 

 Aug. 10 

 Aug. 9 



...do.... 



13 



29 



70.01 



Do... 



...do 



4 



4 



4 



7 



13 



32 



70.11 



Do... 



...do 



4 



do... 



4 



2 



9 



12 



31 



70.03 



Do... 



...do 



4 



...do 



4 



...do 



2 



...do 



9 



12 



31 



70.03 



Do. . . 



July 12 



3 



July 15 



3 



...do 



4 



July 25 



6 



Aug. 8 



14 



30 



69.97 



Do... 



July 13 



4 



July 17 



4 



July 21 



4 



July 27 



6 



...do 



12 



30 



69.97 



Do... 



July 14 



5 



July 18 



4 



July 23 



5 



July 29 



6 



Aug. 10 



12 



32 



70.12 



Do... 



July 13 



4 



July 16 



3 



July 21 



5 



July 28 



7 



Aug. 9 



12 



31 



70.03 



