THIRD REPORT 
Of the Colorado Biological 
Association. 
EDITED BY THE SECRETARY. 
NEW MEMBERS. 
(22.) Win. H. Ashmead, Jackson- 
ville, Florida. 
INJURIOUS INSECTS OF CUSTER COUNTY. 
The Cabbage Aphis, (Aphis brassi 
cae.) — Quite frequently, on the leaves, 
anri especially the outer leaves, of 
cabbages, are found masses of dull 
greyish Aphides or plant-lice, crowd 
ed together as close as possible, and 
living upon the juices of the plant. 
If one of them is examined carefully, 
it is seenv'o have a long, oval body, 
in^color dull greyish-green, but ap- 
pearing whitish because covered with 
a white mealy substance, which is 
readily removed by a drop of alcohol. 
The legs and head are dark grey- 
green — in alcohol they look black. 
Most of these plant -lice are wingless, 
but here and there a specimen will be 
found having wings, whi^h are trans- 
parent, with conspicuous veins. 
The rate 2 which Aphides mul- 
tiply, is something prodigious: 
Dr. C. V. Riley has calculated 
that a single female of the hop-aphis 
may give rise, in a single summer, to 
f trillic s of these insects. He writes: 
•‘Each parthcgenetic female is capa- 
ble of producing on an average one 
hundred young, at the rate of one to 
six, or an average of three per day, 
under favorable conditions. Eeach 
generation begins to breed about the 
eighth day after birth,. so that the 
issue from a single individual easily 
runs up, in the course of the summer, 
to trillions, the issue from a single 
stem-mother may, under favoring 
circumstances, blight hundreds of 
acres in the course of two of, ®ee 
months.” *-'W 
This refers to the hop-aphis, but 
probably the cabbage aphis is not 
much less prolific, and did not nature 
herself provide a. remedy there can 
be no doubt the cultivation of cab- 
bages would become impossible, owing 
to the ravages of " these Aphides. 
There are several parasites which at- 
tack the cabbage aphis, and so effect* 
ually keep it in check; and although 
none of these have yet been observed 
in Custer co.d.°y, there can be no 
doubt that some occur, and will be 
discovered as soon as a iittle patient 
attention is given to the matter. In 
the eastern states and in Europe, 
where the cabbage aphis is also abun- 
dant, the most note worthy of these 
parasites is called Trionyx rapse, a 
small ichneuman fly which lays its 
eggs, one in the body of each Aphis, 
and from these come grubs, which 
live upon the juices of the aphides, 
and eventually turn to flies, which es- 
§ 
I 
