The Cabbage Root Maggot. 



495 



THE ONION MAGGOT. 



Phorbia ceparuni^ Meigen. 



This Anthomyiian has been recognized as a formidable pest by- 

 onion growers, both in Europe and America, since the beginning 

 of the present century. It is probably as widely distributed, and 

 as destructive wherever it occurs, as is the Cabbage Root Maggot. 



The insect is par excellence the Onion Maggot, for it seems 

 never to have been recorded on any other food-plant. Its pres- 

 ence in an onion bed is indicated by the leaves becoming soft and 

 flaccid to the touch, often changing 

 to a yellowish color, and finally wilting. 



The maggot closely resembles the 

 Cabbage Root Maggot (Fig. 2) in size, 

 shape and color. 



The caudal segment, however, is quite dif- 

 ferent in the arrangement and number of its 

 fleshy tubercles ; figure 6, d and <?, represents 

 the caudal segment of the Onion Maggot as 

 seen from the side and from above. There 

 seems to be no difference in the size, number, 

 and arrangement of the dorsal and lateral 

 marginal tubercles in our common root-feed- 

 ing Anthomyiians ; there seems to be always 

 eight small ones. There is often a decided 

 diflference in the two ventral marginal tuber- 

 cles, however, as a comparison of ^, figure 6, 

 and a, figure 2, will show. In the Cabbage 

 Root Maggot these two are always bifid, 

 while in the Onion Maggot they are single 

 pointed. The latter also has, in addition to 

 the two tubercles justcaudad of the vent, two smaller ones on the venter 

 just cephalad of the two large ventral marginal tubercles ; the tips of these 

 small tubercles appear between the larger ones when the caudal segment is 

 viewed from above as shown at e in figure 6. The number of divisions of 

 the cephalic spiracle is usually ten, but sometimes eleven or twelve.* Thus 

 the Onion Maggot is easily distinguishable from the Cabbage Root; Maggot. 



The adult insect, the Onion Fly, closely resembles, but is slightly larger 

 than the Cabbage Fly. Both sexes of the Onion Fly are of ajlight grey 

 color, with the thorax of the male marked with four indistinct Ibrownish 



Fig. 6. — a, b, c, right hind leg of the 

 male of the Onion Fly, the Cab- 

 bage Fly, and the Ftinged Antho- 

 myian, respectively, d, side view 

 of caudal segment of the Onion 

 Maggot ; e, dorsal view of the 

 same. All are much enlarged. 



* I have not been able to compare fresh specimens of the OnionlMaggot ; with such 

 specimens, I presume other distinctive characters would appear. 



