Jan., 1908.] Notes on the Aphididae. I. 247 



great number of aphids had died or migrated the Philotria began 

 to grow again and soon furnished an abundance of food, the 

 return of which was accompanied by the appearance of dark 

 colored aphids. This cycle has been repeated about twice since 

 the middle of October and has not been interfered with or con- 

 trolled in the least. 



In the second series of observations food and temperature were 

 the best that could be provided. In order to have some uniform 

 system of elimination (as all of the individuals of ten successive 

 generations reared would amount to millions) the first individ- 

 ual of each brood was all that was kept. These invariably 

 developed into dark, almost jet black apterous viviparous 

 females. From observing this set of aphids the following 

 points in the life history were noted: The insect requires 

 about twelve days to reach maturity. The first molt occurs 

 about fifty hours after birth; the second two hundred after 

 birth; the third two hundred and thirty; and the fourth three 

 hundred or about twelve days after birth, depending somewhat 

 on the food conditions. For an hour or so before molting 

 the insect crawls about seemingly seeking a dry place in 

 which to molt, but returning at once to the food plant after 

 molting. Immediately following the fourth molt the adult begins 

 producing young which continues from ten to twelve days. 

 This makes the entire life of the individual twenty to twenty- 

 four days, although occasionally an aphid will live several days 

 after it ceases reproducing. By the time the adult dies her young 

 have begun to bear offspring. About five are brought forth 

 every twenty-four hours. This makes fifty offspring for one 

 individual, two thousand five hundred for the second generation 

 and over six million for the fourth generation. This of course 

 is only under the best food and climatic conditions. However, 

 under normal, or even poor food conditions, at least twenty-five 

 individuals from each female will reach maturity if not molested 

 by parasites. 



In summing up the effect of environment on the life cycle 

 under the most favorable food conditions, dark, apterous, vivi- 

 parous females constitute by far the majority of individuals pro- 

 duced, and it seems that the first offspring of a brood always 

 develop into this form, although winged forms may be among the 

 last offspring produced. Under poor food conditions but normal 

 temperature by far the large majority of aphids are winged, the 

 apterous individuals when present being very light in color or 

 only showing faint markings of black. The character and num- 

 ber of the offspring under given conditions is practically the 

 same in the winged or wingless forms, although probably more 

 individuals are produced by the apterous female. Unfavorable 

 food conditions do not call forth the sexual individuals and L 



