14 
BULLETIN 100, IT. S. DEPARTMENT OF AGRICULTURE. 
The maximum number of aphides found on a single leaflet through- 
out the counts was 90, of which 64 were sexual females. This oc- 
curred on the first date of collection. 
It will be noticed from Table V that on the first two dates the ovi- 
parous forms were predominant but that on all later dates these were 
outnumbered by the viviparous individuals. On the date of the 
fourth collection (October 7) numerous sexual females were found on 
the limbs of the tree, and their number was more and more augmented 
each succeeding week. About October 1 the males appeared in num- 
bers, very few of them having been in evidence previous to this time, 
although the first male of the season was noticed July 10. Table VI 
indicates the preponderance in numbers of the sexual female over 
the male. 
Table VI. — Preponderance of the sexual female of Chromapkis juglandh-olaover ihemale. 
Date of collection or count. 
Number of 
sexual 
females to 
each male. 
Date of collection or count. 
Number of 
sexual 
females to 
each male. 
62 
71 
October 24 
13 
23 
November 2 
28 
30 1 24 
9 
5 
( x ) 
October 7 7.3 
14... 5.3 
16 
23 
1 None of either sex seen on leaves. 
Table VI was compiled from the same material as that used for 
Table V. On November 9 nearly all the sexual females were clus- 
tered on the limbs, and two weeks later they and all other plant lice 
at the experimental trees succumbed to a severe frost, which had 
at the same time withered all the leaves. This clustering of the 
sexual females or sexuparse about the limbs explains the small per- 
centage of this form as compared with the males on November 9 
and 16. 
Copulation seems to occur only on the leaf, and the females are*not 
fertilized until they have passed through the last molt. A single 
male may fertilize several females — probably quite a large number 
when it is considered that the latter sex so greatly outnumbers the 
former and that very few eggs prove infertile. Copulation in all 
instances observed by the writer occupied some 30 seconds of time — 
a very short poxiod for an aphis. If the male be disturbed, he will 
immediately retract his genital organ and move off. In 1912 the 
males appeared in comparative abundance in the vicinity of San 
Jose as early as August 26. 
In general appearance the adult oviparous female differs from the 
viviparous form in that it is wingless, has a wider body, and bears 
three conspicuous transverse brown or black bands on the dorsum 
of the abdomen. The male is greenish-yellow, winged, with black 
