AGROMYZID LEAF MINERS — FRICK 373 



All of the 10 Palaearctic subgenera are represented in North America 

 and there are no subgenera pecuHar to this continent. The numbers 

 of species found in each subgenus except Calycomyza are in about the 

 same proportions in the Palaearctic region as they are in North Amer- 

 ica. Subgenus Calycomyza contains only five Palaearctic species whUe 

 it has 17 in North America north of Panama. 



The arrangement of subgenera has always been somewhat arbitrary 

 and was originally based upon a combination of adult and larval char- 

 acters (Hendel, 1931). I have modified the position of two subgenera. 

 Subgenus Amauromyza is placed next to subgenus Nemorimyza and 

 therefore close to subgenus Phytobia. This puts the lai"ger, dark colored 

 species together into a gi'oup of less specialized genera. 



Subgenus Dizygomyza properly belongs with subgenus Icteromyza on 

 the basis of the form of the lunule and close to subgenus Poemyza, 

 according to the recent work of Groschke (1954) and my study of 

 Phytobia (Dizygomyza) thompsoni. Groschke has described species in 

 subgenus Poemyza that have a low lunule approaching those found in 

 subgenus Dizygomyza, while I found a very high lunule in Phytobia 

 (Dizygomyza) thompsoni (fig. 83). However, in spite of the height of 

 the lunule in the latter species, the lunule is in the plane of the frontal 

 vitta and is sharply raised above the mesofacial plate. The highly 

 modified forms of the posterior spiracles of the larvae also indicate a 

 close relationship between these three subgenera. 



Key to the subgenera of Phytobia 



1. Halter with knob white or yellow 2 



Halter with knob partially or entirely brown or black . . 5c. Amauromyza 



2. Lunule low, with height less than one-half the width of the lunule at the anten- 



nal bases (fig. 92) ; if higher, then either frontal vitta entirely bright yellow 

 (fig. 85) or lunule in the plane of the frontal vitta and abruptly raised above 



the mesofacial plate (fig. 83) 3 



Lunule higher, height more than one-half its width (fig. 78) ; frontal vitta at 

 least one-half brown or black and in the plane of the mesofacial plate, some- 

 what sunken below the frontal vitta 5e. Poemyza 



3. Antennal bases widely separated; lunule broad, large, semicircular above, in 



the plane of the frontal vitta, abruptly raised above the mesofacial plate 



(fig. 83) 4 



Antennal bases usually approximate, or if separated, then lunule flattened 

 above, angulate outwardly (fig. 65) ; or lunule smaller, in the plane of the 

 mesofacial plate, somewhat sunken below the frontal vitta (fig. 92) ... 5 



4. Frontal vitta primarily brown or black; frontal triangle not larger than ocellar 



triangle (fig. 83) 5f. Dizygomyza 



Frontal vitta bright yellow; frontal triangle reaching lunule (fig. 85). 



5g. Icteromyza 



5. Vein R4+5 ending nearest wing tip; prescutellar seta developed 6 



Vein Mi+2 ending nearest wing tip; prescutellar absent or not differentiated . 7 



