190 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION. 



on May 30th. About twenty eggs were laid on the vines within this 

 period and the time for hatching noted. About half of these eggs 

 were enclosed in individual cages and an accurate record kept on the 

 whole number. The first nymph hatched on June 17th and the last 

 June 20th, thus requiring a period of from seventeen to twenty days 

 for the hatching period. 



The above records were made on eggs laid by the hoppers which had 

 remained over winter and on the dates given. There was a great 

 difference however in the time required for hatching of the eggs from 

 the spring brood. The observations were made during July and August 

 and included records on two or three hundred eggs. The period 

 required for hatching here was from eight to twelve days, all of the 

 two or three hundred eggs coming within this limit. We can account 

 for the difference only in the higher temperature of the later months 

 or in the character of the eggs from the two broods. There was not 

 much difference between the temperature in June and July in the 

 Lodi section, hardly enough to account for all the difference in embry- 

 onic development. It may be possible that the vigor of the adults and 

 the increased development of the egg when laid will account for this 

 difference over the spring brood. 



The time required for the eggs to mature in the ovaries was de- 

 termined as from five to seven days A number of pairs in coitu were 

 liberated in the cages and the first eggs laid in five to seven days later. 



Percentage of Eggs that Hatch. The table indicating rate of ovipo- 

 sition on page above shows that of the first sixty-three eggs laid every 

 one hatched. The hatching was less accurately kept for the remainder, 

 but we are quite sure that every egg laid by this particular hopper 

 brought forth a nymph. In the case of forty eggs laid by another 

 hopper, all hatched. With the layings from most of the hoppers in our 

 breeding cages a very high percentage of the eggs matured. This was 

 not true of all, however. In one case a hopper laid a total of thirty-five 

 eggs, scattered along over a period of three weeks, and only five out 

 of the thirty-five hatched. In another case fourteen eggs were laid by 

 an individual and none hatched. This experience in the laboratory 

 of a very large percentage of mortality in some layings was also 

 observed in the field. On one side of a particular vineyard where 

 hoppers were exceedingly abundant in 1907, the worst infested field 

 seen during the season, there was a very great mortality in the egg 

 stage. On a single leaf taken from this particular area we have 

 counted a total of seven hundred and forty-seven eggs that failed to 

 mature. These could be very readily detected on the leaf by the dead 

 epidermis covering them, which was dark brown to black in color. 

 The leaf was thoroughly sprinkled with these black areas, and showed 



