BULLETIN 263 



SYRPHIDAE OF MAINE. 

 SECOND REPORT: LIFE HISTORY STUDIES.^ 



C. L. Metcalf.2 



The investigation of the biology, ecology, and economic 

 status of the Flower-flies of Maine, the first report of which ap- 

 peared as Bulletin 253 of this station, has been continued during 

 the summers of 1916 and 1917. The data secured on the follow- 

 ing species seems of sufticient interest to warrant publication at 

 this time. 



The species discussed below are all aphidophagous, depend- 

 ing for growth and development on aphids, which are ravenous- 

 ly devoured during the larval stage of the fly. They must there- 

 fore be recognized as beneficial insects and their presence in any 

 locality must be looked upon as an agricultural asset of no mean 

 importance. To illustrate, — in an experiment with one of the 

 species described below (see page 156) the writer found that, in 

 five hours less than two days, three larvae had devoured a total 

 of 325 plant-lice, or an average of not less than 54 a day for each 

 larva. There is no reason to believe that this record is in any 

 way exceptional. In fact in this case the thoroughness with 

 which the aphids were devoured indicated a still greater capacity 

 of the larvae. 



So far as I am aware no previous record has been made of 

 the metamorphoses of these species. 



The species, Syrphus oronoensis, appears to be an impor- 

 tant predator of the aphids affecting stone fruits ; the species 

 Xanthogramma divisa and Syrphus knabi are, so far as observed, 

 of more benefit to certain shade and forest trees ; while the cho- 

 sen food of Platychirus perpallidus has not been determined. 



The latter species is of faunistic interest since it is not hith- 

 erto recorded outside of Britain. I have also taken the follow- 



^Papers from the Maine Agricultural Experiment Station: Entomol- 

 ogy No. 94. 



"Member of the Station Summer Staff. 



