THE CANADIAN ENTOMOLOGIST 53 



OBSER\ATIONS ON THE MORE COMMON APHIDOPHAGOUS 



SYRPHIU FLIES. (DIPT.). 



BY C. HOWARD CURRAX, 

 Dominion Entomological Laboratory, Vineland Station, Ontario. 



During 1913 at Guelph, 1914 at Orillia, and 1915 and 1919 at Vineland, 

 thf immature stages of many species of Syrphidie, but more especially the 

 aphidophagous or aphid-eating forms, have been studied by the author. As 

 the study of these flies is of considerable interest to the fruit grower and gardener, 

 owing to their beneficial habits, the observations made chiefl\' concern such 

 species as were found to be of the greatest economic importance 



Species belonging to four genera, Syrphus, Allograpta, Sphterophoria, and 

 Paragus have been especially studied with the view of obtaining information 

 as to their importance in the natural control of aphids injurious to farm crops. 

 No suggestion is made here that any one species is of greater importance than 

 another, although it is quite evident that the species discussed are of more 

 importance than others, due to the fact that they are, for the most part, very 

 common. 



It has been found that Syrphid larvae of all species are more or less heavily 

 parasitized, some years much more severely than others. During 1919 parasites 

 were over twice as numerous as during 1915. 



Difficulties occur in the study of these larvae, such as the almost complete 

 absence of food at some periods of the year. Thus, during the past season, 

 Svrphid larvae were particularly numerous on small aphid colonies early in the 

 summer, but it was found to be impossible to secure sufficient aphids for food, 

 as some species cannot thrive, except on a particular type of aphid. But during 

 the early part of the past season: even general feeders, such as Syrphus ameri- 

 canns, could not be reared successfully. 



The eggs of aphidophagous Syrphidae are laid singly on the leaves or stems 

 of plants, either in or near an aphid colony. They are creamy-white, but in 

 many cases become grayish after one or two days. They vary in size according 

 to the size of the fly. 



The larvae are more or less flattened beneath, without true legs, and often 

 with fleshy, spine-like protuberances. They vary in shape, colour, size and 

 convexity, according to species. 



The pups of our common species resemble each other to a considerable 

 extent. Pupation, however, may take place either in the soil, or on the plant. 

 In one case, at least, it occurs in either place. 



The more important species are dealt with regarding their feeding habits 

 and abundance. 



Allograpta obliqua Say. This is one of our most common syrphus flies 

 and is common during the whole season, from May until October. 



The larva is a very general feeder, having been found during the past season 

 fn Aphis brassiccB, A. rumicis, A. cardui, A. pomi, A. gossypii, Myziis cerasi, 

 Macrosiphum, sp. on wild lettuce (Lactiica canadensis) and Macrosiphuni sp. 

 on wild aster [Aster spp.). 



On all hosts except Aphis pomi this species was very abundant. In the 



March, 1920 



