194 



UNIVERSITY OF CALIFORNIA EXPERIMENT STATION. 



From the above table it will be seen that the shortest time required to 

 go through the five nymphal stages is sixteen days, and the longest 

 period nineteen days, the average being about eighteen days. 



Summarizing the duration of each of the stages as given above, 

 it will be, disregarding fractional days, as follows: 



The total length of the nymphal life of the grape leaf-hopper in 

 New York, as worked out by Slingerland, 1 is from thirty to thirty-three 

 days. This is a difference of about two weeks from that of the same 

 species in California. Climatic conditions probably account for this 

 difference, although so far as temperature is concerned, there is not 

 much difference between the section about Lodi in June and July and 

 that of New York in the same months. 



Molting. As a preliminary step to the actual shedding of the skin, 

 the nymph becomes quiet for a short period, then the old skin splits 

 on the thorax and the nymph with its new covering makes its way 

 out. The actual working out from the old skin required about ten 

 minutes, and in a very short time thereafter it is. able to move about 

 as usual. Immediately after emerging from the old skin the insect is 

 white in color and fairly transparent. The tracheal system can be 

 followed very readily, especially in the younger nymphal stages, after 

 emerging from its old integument. During the process of emerging 

 the old skin seems to be held on to the leaf by the claws of the feet, 

 and these often remain for some time attached to the leaf. The last 

 nymphal skin, however, is much more firmly attached than the earlier 



Cornell Exp. Sta. Bull. No. 215, p. 92. 



