50 PROCEEDINGS OP THE NATIONAL MUSEUM vol. 68 



way on the keel of the median stylet, so prominent in Thompson 's 

 figure, are lacking in my specimens. In the buccopharyngeal appa- 

 ratus, the same parts occur, and in very nearly the same relative 

 size and conformation as in the various species of Senotainia. The 

 cuticula is found to possess, on every segment, an anterior band of 

 flat, nearly transparent microscopic scales followed by a wider band 

 of longitudinal corrugations, as in Senotainia. There are no heavily 

 chitinized spines on the cuticula at any point. The uterine larvae 

 are about 0.8 mm. long and the buccopharyngeal apparatus is one- 

 fourth the length of the body. The other larval instars and the 

 puparium of this species have not been studied. 



The adults frequent sunlit, barren spots on low fertile soil sur- 

 rounded by luxuriant herbaceous vegetation, such as denuded 

 spots in a weedy field, or in such crops as rape and cowpeas. In 

 such places the adults may be found in large numbers, darting 

 about just above the surface of the soil, alighting now and then on 

 the soil or on short dry sticks arising from the ground. They are 

 not known to be attracted to flowers. On one occasion they were 

 found in great abundance on rape, apparently attracted by a flow 

 of honeydew from the heavy infestation of plant lice present. 



M. leucocephala has been reported parasitic in the nests of the 

 "sweat bees," on Halictus sexcinctus in Pomerania ^^ and on H. 

 pruinosus in Massachusetts.-" The latter record is by Melander and 

 Brues, who state that the adult fly chooses ''the moment when the 

 incoming bee pauses at her threshold, quickly and quietly to oviposit 

 on her pollen mass and thus infect her offspring." This species has 

 also been observed hovering over the burrows of Chlorion atratum 

 Lepeletier while the latter was digging in sand " and Adams is 

 credited with the observation that the larvae of Chlorion ichneu- 

 moneum are devoured by the Metopia maggots.^^ Bezzi states that 

 in Europe, M. leucocephala has been reared from Bembix, Halictus 

 and Philanihus?^ 



METOPIA OPACA, new species 



Male. — Front 0.39 of head width (measurements of five 0.37, 0.38, 

 0.40, 0.40, 0.40); vertex and upper part of parafrontals dull black, 

 sharply defined from the dull leaden gray pollen of the anterior 

 portion of parafrontals w^hich is continuous down over face and 

 bucca; frontal vitta black, not obliterated anteriorly, but narrowed 

 to near base of antennae where it is nearly as wide as ocellar triangle, 

 at level of lowest orbitals it is third width of parafrontal; about eleven 

 bristles in frontal row which extends to below insertion of arista, 



» Ridel, Allg. Zeitsch. f. Ent., vol. 6, p. 152. 



2« Biol. Bull., no 5, p. 20, 1903. 



27 Adams, 111. Nat. Hist. Surv. Bull., no. 11, p. 195, 1915. 



2' Rau and Rau, Wasp Studies Afield, p. 197, 1918. 



20 Bezzi and Stein, Kat. Pal. Dipt., vol. 3, p. 511, 1907. 



