THE MEALY PLUM APHIS, 7 
usually deposit young within a very few hours after shedding the 
final skin. 
A minimum-generation series of last-born aphids is indicated 
below: 
TABLE 111.—Development of minimum-generation series of the mealy plum aphis. 
Walnut Creek, Cal., 1916. 
Genera- 
s Date of | Develop- 
tion of | Date of | fourth | menta 
sada: birth. molt. | period. 
Taso tcc| boeken eee Mars Sisles ose. 5.5 
WELLE See are 21| May 3 12 
Tse ay 29| June 11 13 
TVS eee July 1) July 12 il 
These four generations were completed in about four months, or 
over a month longer than the seven generations of the first-born 
series. 
The period of reproduction as indicated in the foregoing table 
varied from 20 to 26 days. 
REPRODUCTION. 
Observations were made on the reproduction of individuals of 
wingless generations 2 to 5 inclusive. Adults of the second genera- 
tion, for a total reproductive period of from 4 to 5 weeks, averaged 
about 4 young daily, producing the first three weeks a daily average 
of 6 young. The later generations were less prolific, fourth and 
fifth generation individuals not averaging above 24 young per day. 
Ten young were deposited within 24 hours on several occasions, but 
on no occasion was this number exceeded. The rise and decline in 
fecundity was in the main similar to that found in the case of the 
stem mother. 
HABIts oF SPRING GENERATIONS. 
The aphids of the second generation, when newly born, dispose 
themselves in groups, close by the parent, on the underside of the 
leaf. After the first molt many remove to other leaves and this is 
the beginning of the migration from leaf to leaf and branch to 
branch. Second-generation larvee and adults prefer to suck the 
rib tissues of the leaf. Owing to the rapidity of reproduction and 
consequent crowding, the aphids of later generations have little choice 
of location and feed at any point on the lower surface of the leaves 
or on petioles. If the lower surface of a leaf is entirely occupied 
many larve will be found feeding on the upper surface, in some 
cases apparently in preference to seeking other less crowded leaves. 
