342 
The Ohio Naturalist. 
[Vol. XI, No. 7, 
outlined extending practically the full length and varying in 
width. At the approach to metamorphosis these adipose masses 
increase in extent sometimes covering nearly the entire dorsum 
except the blood-vessel. At times also the body fluid invades 
more or less the fatty bodies appearing as outlying pulsating 
pockets. 
This fly is abundant in this region and has been taken from 
April 1 to September 10. The stages have not been followed 
throughout the year and the egg has not been studied. 
The autumn generation of larvae appears on cabbage affected 
by plant lice usually during the latter half of September, becom- 
ing abundant from the first to the middle of October. During 
the fall of 1909 the study was not taken tip until about the middle 
of October. At this time larvae were plentiful and were found at 
the University farm until the first of November when the host 
plants were removed. When the writer returned to Columbus 
the middle of September, 1910, very few aphids or larvae of 
Syrphidae were to be found and none of Syrphus torvus. The 
latter appeared after those of other species, not becoming abund- 
ant until the first week in October. They were still fairly plen- 
tiful the middle of October. 
I have not determined die duration in the larval stage. Some 
larvae taken Octover 15 and kept on sparse diet remained 
unchanged December 3, showing their great tenacity of life. 
The larvae live on cabbage and related plants crawling about 
on the surface of the outer leaves and as far inward as is accessible 
without boring. The food of the larvae is usually the body juices 
of the cabbage plant-louse ( Aphis brassicae Linn). I have found 
some of this species on Sycamore feeding on Longistigma caryae 
but they are much more abundant on cabbage. Confined larvae 
readily change to the latter kind of food in absence of the cabbage 
aphids. The larvae are sometimes found on plants on which 
there are no aphids; but usually there is an abundance of prey at 
hand. 
The louse is seized by the hooks and jaws of the mouth of the 
larva and held in the air while the juices of its body are sucked out. 
I have found no particular enemies of this stage. They are often 
well protected from birds among the inner leaves. 
PUPA. 
In changing to the pupa the larval skin contracts to form a 
puparium. The body becomes shorter, more oval, expanded 
dorsally in front and of a darker color. Length 8-8.25 mm., 
width 3. 5-4. 3 mm., height 3.75-4 mm. Testaceous brown, naked, 
smooth except for slight remains of the transverse wrinkling of 
larva. (Fig. 14). Broadest in front of the middle, nicely rounded 
in front, descending rapidly at the posterior end to the projecting 
caudal spircales (Fig. 15). 
