BIOLOGICAL STUDIES ON THREE APHIDID^. 



161 



As shown in Table XI, a longer time was required to reach ma- 

 turity in the cooler parts of the season. The average number of 

 days required for development during the first of the season — that is, 

 to July 1 — was 15.9-|- ; during the warmer part of the year (July 1 to 

 September 1) it was 8.G+ ; while during the period between Sep- 

 tember 1 and 21 it was 10.3 days. Both the length of life and the 

 productive period vary in relation to temperature and season, being 

 longest in the cooler parts of the year. The maximum period for the 

 production of young, in my 79 experiments, was 52 days, while the 

 average Avas 27.6-1- days. The maximum length of life of individ- 

 uals in these same experiments was 101 days and the average was 

 49.6-f- days. Larger numbers of young are produced per day in the 

 warmer parts of the year than in the cooler and later months. The 

 total number of young produced by 79 females was 4,896 — an aver- 

 age of 61.9-|-. The largest number of young per single female was 

 89, and the average number produced in one day was 2.5-]-. The 

 largest number of young produced in one day by a single aphis was 

 9. Almost without exception, the mother aphis lived several days 

 after the production of the last young. The number of molts was 

 invariabl}^ 1, and, as will be seen in the accompanying table, they 

 occurred, almost without exception, every two days. 



Table XII. — Periods of molts of >^iplia flava, vii-iparous generation, 190G. 



Date of birth. 



August 9.. 

 August 4.. 



Do.... 

 August 12. 



Do.... 



Age at 

 birth of 



first 

 young. 



Days. 



OVIPAROUS GENERATION. 



The first individuals of the oviparous generation to be noticed 

 were born September 24, 1906, although in 1905 aphides of this gener- 

 ation were found as early as August 25. In all cases it required a 

 longer time for the individuals of this generation to become adults 

 than it did for those of the viviparous generations, excepting the 

 stem-mothers, this presumably being largely due to temperature, 

 groAvth being slower in the cooler parts of the year. The length of 

 the immature stages varied from 15 to 40 days, the latter time, how- 

 ever, being very exceptional in length. 



