Biology of the Membracidae of the Cayuga Lake Basin 413 



These figures show that only two species, Ceresa huhalus antl Ophiderma 

 puhescens, appeared earlier in 1915 than in 1914. Two others, Telamona 

 ampelopsidis and Entylia bactriana, appeared on the same dates in both 

 years, but each required a longer period for development in the colder 

 season than in the warmer. The evidence is thus fairly conclusive that 

 cold as well as dry weather is detrimental to the hatcliing of eggs. 



Like results were obtained in the study of the length of njaiiphal instars. 

 The record for Thelia bimaculata for 1914 and 1915 was as follows: 



Thelia bimaculata 1914 1915 



First instar 6-7 days 6- 7 days 



Second instar 5 6 



Third instar 6 6 



Fourth instar 6-7 7 



Fifth instar 7-12 9-16 



Total 30-37 days 34-42 days 



Since the year 1914 offered favorable conditions in moisture as • well 

 as in temperature, it is likely that the results obtained for that year were 

 influenced by both conditions and it is of course impossible to determine 

 the part played by moisture and temperature separately. The nearest 

 approach to such a determination seems to be the comparison with records 

 for some year in which normal conditions prevailed, which may })e used 

 as a check. The year that most nearly approached such conditions 

 during the period embraced by this study was 1912. The average annual 

 temperature for the basin, computed for a period of forty-one years 

 since 1876,^ has been found to be 47.2° F.; the average temperature for 

 1912 was 46°. The average annual precipitation for the same period 

 was 33.44 inches; for 1912 the precipitation was 32.95 inches. Taking 

 the year 1912 as a check, the field records show that the dates of first 

 collection of the nymphs of the various species mentioned are very regularly 

 between those of 1914 and 1915, while the length of the five instars of 

 Thelia himaculata averaged, respectively, 6, 5, 6, 6, and 12 days. 



Variations in temperature seem to have little effect on the adults except 

 that they appear more active in warm weather and remain later in the fall 

 when the months of September, October, and November are warm. Many 

 species have been collected in the field some time after the first few snows 



6 Monthly and annual meteorological summary and comparative data of Ithaca, N. Y. Weather 

 Bureau Office, Ithaca, New York. December 31, 1916. 



