ORDER DIPTERA 239 



that have been deposited there by aphids or other insects. 

 They also suck nectar from flowers. Some of the female 

 Agromyzidae have a peculiar habit of making holes in the 

 leaves with their ovipositors and then turning about and 

 sucking the juice from the host. 



A Key to the More Common North American Leaf-Mining Diptera, 

 Based on Type of Mine Produced 



1 . Linear or serpentine mines, at least in part linear 2 



Blotch mines, the linear part becoming obscured immediately 17 



2. True linear or serpentine mines 3 



Linear -blotch mines 15 



3. Mines comparatively short, broad, seldom tortuous 4 



Mines long and more or less tortuous 10 



4. Mines occurring on upper side of leaf, the larva escaping through a 



crescent-shaped slit 5 



Mines on lower side of leaf, or alternating from upper to lower side ... 6 



5. Frass usually prominent, on Aster a prominent frass line, on Symphori- 



carpos ace?nosus and Heracleum lanatum not so prominent 



Phytomyza albiceps 

 Frass not prominent, scattered; mine varying from linear to linear- 

 blotch and blotch ; occurring on a large number of host plants 



Agromyza pusilla 



6. Mine on lower side of leaf, white, narrow at first, later becoming broad 



and almost blotch-like; frass in distinct spots; occurring on Populus 



species An undescribed species 



Mine distinctly visible from both surfaces of leaf 7 



7. Mine very broad, almost a blotch 8 



Mine narrow, thread-like 9 



8. Mine white, visible for its entire length from upper and lower side of 



leaf; occurring on Smilacina racemosa An undescribed species 



Mine alternating from upper to lower side of leaf, never visible from 

 both sides at the same time Agromyza parvicornis 



9. Mine deep, conspicuous, later becoming red in color, alternating from 



upper to lower side of leaf ; occurring on grasses . . Cerodonta femoralis 



Mine shallow, inconspicuous, white in color, alternating from upper to 



lower side of leaf; occurring on Iris Agromyza laterella 



10. Mine with a conspicuous central dotted frass line 



Phytomyza obscurella var. nigritella 

 Mine with or without a frass line, but never with a dotted frass line . .11 



11. Mine on under side of leaf, white in color; puparium formed in leaf; 



occurring on Lactuca scariola var. integrata. . . Phytomyza lactuca 

 Mine on upper side of leaf 12 



