76 
Sanderson, in Delaware, found almost all the piiparia of Allo- 
grapta obliqua to be parasitized by Bassus Icetotorius Fab., and from 
several puparia which seemed to have been parasitized by the Bassus 
were bred the chalcid Pachyneuron syrphi Ashm. B. Icetotorius is also 
])arasitized by Isocratus vulgaris Walk., according to Fletcher. 
A. obliqua is a common species in Illinois, where the larva feeds 
on M. pisi as well as on other aphids. 
Syrphus aniericanus Wied., one of the largest species of the 
family, has conspicuous bands of black or yellow, and buzzes like a bee 
when on the wing. The larva is greenish or mottled brownish, at- 
tains a length of half an inch or more, and pupates on the plant or 
a little below the surface of the ground, as Johnson noted. The 
species deposits a single small oval white egg in a colony of plant-lice, 
and one of the larvae has been observed to eat t\yenty-five plant-lice in 
as many minutes, according to Sanderson. In Delaware, he found it 
to be extremely abundant as an enemy of M. pisi; in Illinois, it feeds 
on the same species and is frequent but not conspicuously numerous. 
Syrphus ribesii L. is reported from Canada, by Fletcher, as an 
abundant foe of the aphid, and as being attacked by Bassus Icetotorius, 
which, in turn, falls prey to the chalcid Isocratus vulgaris. S. ribesii 
occurs with us, but I have never happened to take it in the clover field. 
Sphcerophoria cylindrica, a small syrphid named by others as 
aflfecting M. pisi, is rather common here in aphid-infested clover fields. 
Mesogramma politum (Fig. 7, 8) is frequent in our clover fields, 
the green larva feeding on the clover-louse. A full-grown larva found 
on the ground March 27, made its puparium the same day, and the fly 
issued indoors April 8. 
Fig. 7. 
Fig. 8. 
Syrphus-fly, Mesogramma politum: Fig. 7, adult; Fig. 8 (a), larva, 
(b) puparium. (Riley and Howard, U. S. Dept. of Agriculture.) 
Mesogramma marginatum has similar habits and is common. A 
puparium found on a clover leaf June 21 yielded the adult June 22. 
Platychirus quadratus, a small and frequent species, and the less 
common Ocyptamus fuscipennis, I have taken in sweepings, along with 
the abundant M. pisi. It is probable that their larvae feed on the 
clover-louse. 
