W. M. DAVIDSON 47 



abruptly so on the anterior end, behind descending in an 

 even curve to the cauda; venter gently concave; body narrowing 

 caudad so that at the base of the posterior respiratory tubes its 

 width is half that at the widest part-anterior third. 



In Mfiy 1920 three individuals passed the pupal stage respect- 

 ively in sixteen, sixteen, seventeen days. 



The cycle, egg to adult, occupied about forty-two days for 

 this species. This cycle is about as long as that of M. chaetopoda 

 but shorter than that of M. stegnuin Say. 



The cjuestion as to whether the larvae of IMelanostotnae are 

 normally entomophagous has been referred to above. Prof. C. 

 L. Metcalf found that in Maine those of Melanostoma mellinum 

 Linnaeus readily ate the aphids Mrjzus persicae Sulzcr and Aphis 

 cornijoliae Fitch, but refused several other species"'. ]\Ir. C. 

 Howard Curran in a letter to the writer stated that in Ontario 

 he found that the larvae of M. obscurum Say consumed both 

 aphids and decomposing chickweed, and that they were more 

 successful on the latter diet. In this connection it can be said 

 that from the writer's observation the young larvae of the well- 

 known aphidophagous syrphid Allograpta obliqua Say, are alile 

 to sustain themselves at least through the first few days of their 

 larval life on ]ilant food. In the cages at Alhambra there? was 

 no decomposing plant matter and the female Mclanosto)na 

 flies deposited all their eggs on the plants, indicating some at- 

 traction to the aphids or to the healthy plants. While the in- 

 dividuals of M. stegnum raised on a diet of aphids Ijccame uiuKm-- 

 sized imagines, those of the other two species bccime normal 

 adults. It is possil:)le that several of the species of Melanostoma 

 are both ])hytophagous and entomophagous in tlie larval stag(% 

 and even that these are inidergoing a transition in hal)i1, chang- 

 ing from plant- to insect-feeders. The nocturnal hal)it of teed- 

 ing and desiie for concealment suggests that it may not have been 

 so long ago that the larvae normallN' lived in obscurity inside 

 plants, or in the open in darker situations than growing i)lan(s 

 normally afford. 



Explanation of Plate I 



Fig. D. — E{>;gs of Mdnnodnnxi slcgnuin Willi.ston on I)c;in leaf. Photn- 

 graph taken at Alhaml)ra, California, March '20, 1920. 



Fig. E. — Melanosloina obscurum Say, var. ro.slrahau I5i!j;<)l. I'lill giown 

 larvae. Photograph taken at Alluunhra, California, Ajiril 27, l',)20. 



3JMe. Agr. Exp. Sta.. Bull. 253, "Syrphidae of Maine." 



TRANS. AM. ENT. SOC, XLVIH. 



