June, '15] 



RICHARDSON: THE CORN-FEEDING SYRPHUS FLY 



341 



Along midrib, upper surface of leaf 

 Along midrib, lower surface of leaf . 

 On blade of leaf, upper surface . . . . 

 On blade of leaf, lower surface .... 

 At tip of corn ear 



31 pupae. 



4 

 13 



1 " 

 5 " 



Other pupae were found at later dates in the axils of the leaves, and 

 in the sheath surrounding the ear, but they were invariably more 

 numerous on the upper surface of the leaf. Sanderson and Met calf 

 have observed many pupae on the tassels, but this was certainly not 

 the preferred place for pupation at Jobstown. 



Natural Enemies. — The most important enemy of the corn-feed- 

 ing Syrphus fly was a disease which appeared to be particularly fatal 

 to mature larvae. Dead individuals were to be seen on nearly every 

 corn leaf and on the stalks in places where the larvae were particularly 

 numerous. Sanderson mentions an apparently similar epidemic in 

 Delaware. 



While a larva of Megilla fuscilahris was found but once in the act of 

 devouring a pupa of M. polita, there can be no doubt that it was an 

 active enemy of the corn-feeding Syrphus fly because of its abundance 

 in the corn fields and the large number of pupal remnants which showed 

 the visitation of a predaceous insect. 



Although a large number of pupae were reared and many dissected, 

 no internal parasites were found. In a few cases, eggs placed on 

 leaves showed holes through which egg parasites had escaped. 



Discussion. — Mesogramma polita has apparently never been inju- 

 rious to corn in New Jersey or Delaware. Reports of injury have 

 come, however, from Florida and Missouri and it seems that the feed- 

 ing habits of this species will require closer attention in many localities 

 before its exact economic status can be determined. 



The observations of Folsom are particularly important because they 

 indicate a hitherto unknown feeding habit for this species.. If M. polita 

 proves to be commonly predaceous then Metcalf's acceptance of it as 

 a purely phytophagous species cannot be upheld. The close relation- 

 ship of the genus Mesogramma with the aphidophagous genera, Syrphus 

 and Sphcerophoria as indicated by Riley and Howard ^ and the general 

 resemblance of the larva to other predaceous Syrphid larvae suggest 

 its derivation from predaceous ancestors. This conception is further 

 strengthened by the fact that Mesogramma marginata Say ^ is also 

 predaceous in habit. 



Loc. cit., 1888. 

 2 Folsom, loc. cit. 



