342 The Ohio Naturalist. [Vol. XI, No. 7, 



outlined extending practicalh' the full length and var^'ing 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 1(J. 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 up until about the middle 

 of Octol:)er. At this time larvae were j^lentiful 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 tonus. 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 the 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 abtnidant on cabbage. Confined larvae 

 readih' 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 lar\'al skin contracts to form a 

 puparium. The body becomes shorter, more oval, expanded 

 dorsally in front and of a darker color. Length S-S.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). 



