726 RoBert MATHESON 
1914 the earliest date on which stem mothers became mature was May 16, 
and this corresponded with the first unfolding of the blossoms. 
The mature stem mothers are very inactive. They settle down and 
content themselves with pumping out the plant juices and producing 
young at a most phenomenal rate. When disturbed they quickly remove 
the proboscis from the plant tissues and seek out another spot in which 
to continue their operations. 
Reproductive period 
The stem mothers become mature in about two weeks after hatching; 
the length of time depends largely on weather conditions, tho under the 
most favorable circumstances nearly two weeks are required. The pro- 
duction of young usually begins in two or three days after the last molt, 
and continues without interruption for over a month. The stem mothers 
are remarkably hardy and their productive capacity is wonderful. As 
the warm, sunny days of spring come on, the plant louse seems to turn 
into a reproducing machine, and each morning the worker is filled with 
astonishment as he carefully removes and counts the overnight progeny, 
seemingly greater in bulk than that of the mother. This rate of produc- 
tion continues day after day, as may be seen by consulting Reproduction 
Chart II. In these experiments the average daily production thruout 
the productive period was 5.45 for four individuals. The greatest 
number produced in one day was 33, while the average length of the 
productive period was 33.5 days. The total production of young by the 
various individuals varied from 131 to 244, with an average of 184. 
In the case of this species the period of reproduction extends from about 
May 10 to June 20 or later. As the eggs of this species hatch over a period 
of ten or more days, undoubtedly the last stem mothers to hatch are 
still producing during the last week of June. However, the maximum 
period of productive activity is during the last week of May and the first 
week of June, that is, while the young fruits are beginning to set and start 
active growth. 
Description of stages 
First instar (Plate XVIII).— Average length 0.6 mm.; average width 
0.3mm. (There is considerable variation in these measurements, depend- 
ent on the age of this instar.) 
