THE MEALY PLUM APHIS. - 9 
Antenne four-fifths as long as body, on frontal tubercles. Comparative 
measurements as follows: I, 0.08 mm.; II, 0.06; III, 0.405; IV, 0.26; V, 0.21; 
Vi, 0.48 (0.0 plus 0.88). Beak reaching a little beyond anterior border of 
mesosternum, 0.26 mm. long. Wings 2.5 mm. long. Cornicles faintly imbri- 
eated, shorter than in wingless female, barely twice as long as broad at base, 
slightly constricted near base, in length 0.08 mm. Style ensiform, 0.15 mm. 
long. Length of body, 1.61 to 2 mm.; width, 0.66 mm. 
Lateral tubercles as in wingless form; first antennal joint somewhat gibbous. 
Sensoria.—On III, 28 to 30; on IV, 4 to 10; on V, 1 to 2; on VI, usual apical 
group. Sensoria of unequal size, not at all arranged in longitudinal rows, but 
rather in spirals. 
DURATION OF NYMPHAL STAGES. 
Eight winged spring migrants developed in an average of 144 days, 
the developmental period ranging from 13 to 18 days. The winged 
form therefore develops more slowly than the wingless, due to the 
increased duration of the fourth instar. 
REPRODUCTION. 
The migrants commenced to reproduce on the cat-tail rush (Typha) 
a few days after they settled. In many cases migrants were found to 
settle, remain for several days, and finally die without reproducing 
and only a small percentage of those settling reproduced. Most of 
them remained a few days and then departed. Spring migrants in 
only one instance out of 76 deposited young on caged plums. In this 
instance the three young born refused to feed on the plum (Myroba- 
Jan). in this connection it might be said that all attempts to induce 
wingless forms of earlier generations to settle on Typha failed. Mi- 
grants placed in small dishes and provided with plum and cat-tail 
foliage in no instance deposited young and in extremely few instances 
did migrants placed on cat-tail deposit young. Unfortunately it was 
not possible to obtain Phragmites for similar tests. 
The migrants may remain on the winter host foliage for several 
days before taking flight, especially if the weather be cool and cloudy. 
Field observations indicated that the migrants produced young 
at the rate of about five every two days at first, and later at a slower 
rate. On Typha it appeared that the maximum number of young 
per migrant rarely exceeded 20 and, discounting all migrants which. 
failed to deposit, averaged not much over five. This must have been 
abnormal, as examination of individuals disclosed the presence of 
many more embryos than were extruded. It is possible that Typha 
does not prove an invigorating food for the migrant and this point 
is perhaps elucidated below in the paragraphs on migrations. 
MIGRATIONS. 
Phragmites and Arundo have long been known as alternate hosts 
of the mealy plum aphis; in fact the species has been described as 
new from both of these hosts. In California enormous infestations 
