SYRPHIDAE OF MAINE. 213 



"The real importance of the Syrphus-fly larvae in the reduction of 

 the species [the pea-louse] was shown beautifully in southern Mary- 

 land, where they were so abundant the first and second weeks in June 

 as to almost completely destroy the lice." And quoting further from 

 his correspondent: "The insects (lice) started to disappear last 

 week and are now about all gone . . . The last few days I packed, 

 the separators sieved out about 25 bushels of green worms [larvae of 

 Syrphidae, chiefly Allograpta obliqua] which no doubt proves that they 

 destroyed the lice.' " 



Mr. Johnson states further that the Syrphid-flies did not save 

 the crop that year but calls attention to their probable value in 

 relation to future ravages of the pest. A conservative estimate 

 shows that twenty-five bushels of the larvae of Allograpta 

 obliqua could scarcely represent less than 3,000,000 individuals. 

 Presuming that the larvae lived ten days and ate on the average 

 twenty aphids a day (which I believe also to be a conservative 

 estimate) such a multitude of larvae would be responsible for 

 the destruction of over half a billion aphids. 



Another example of the extermination of aphid colonies by 

 these predaceous larvae is afforded by the attacks of Pipiza 

 pisticoides on the Woolly Apple Aphis. These aphids became 

 evident as above-ground colonies on apple, at Orono, about the 

 first of August. At the same time several species of Syrphid 

 larvae also made their appearance among them, chiefly the larvae 

 of Pipiza. m Shortly the Woolly Apple Aphis began to disappear, 

 the aphids becoming scarcer and scarcer and the predaceous 

 larvae more and more evident, until by early September I found 

 myself with many larvae on hand and almost no aphids any- 

 where to be found as food for them. Doctor Patch tells me 

 she has found this a rather common experience ; and that year 

 after year, the colonies of Woolly Apple Aphis on apple have 

 practically disappeared in the presence of these predaceous 

 larvae, by mid-September. See also page 224. 



The relentlessness of these enemies of aphids is illustrated 

 in a peculiar way by the experience of the Station Entomologist, 

 who for a number of years has been studying the aphids of the 

 State. It is an altogether too common experience that aphid 

 material mailed to her for study has been absolutely consumed 

 en route by Syrphid larvae, inadvertently introduced into the 

 package by the correspondent. 



