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 I 
