138 MISC. PUBLICATION 174, U.S. DEPT. OF AGRICULTURE 



HOSTS AND LIFE HISTORY 



Besides the hessian fly, the only other known hosts for Pleurotro- 

 pis metallicus are Oscmetla frit (Linnaeus), first recorded by Collin, 

 and later mentioned by Meyer and Imms, and Mayetiola phalaris 

 Barnes recently recorded by Blunck. 



Little is known of the life history, but it is believed to be a 

 primary, solitary, internal parasite. McConnell states that he ob- 

 tained emergence of adults in cages from April to June, inclusive, 

 and from September to December, inclusive. Emergence is from 

 the puparium of the fly. 



DISTRIBUTION 



Apparently this species is widely distributed in Europe, having 

 been recorded from various parts of Russia, from Germany, and 

 from the British Isles. 



In North America, as has already been stated, Wade and Myers 

 listed 13 States in which it had been found up to 1921. These States 

 were Virginia, Maryland, Delaware, New Jersey, Pennsylvania, New 

 York, Ohio, West Virginia, Indiana, Michigan, Illinois, Oregon, 

 and Washington. Fletcher in 1900 and Treherne in 1916 recorded, 

 what was probably this species from Prince Edward Island, Canada. 

 So far as the writer is aware, no additional records have been secured 

 that would extend this knoAvn distribution. 



The presence of the species in most of the area indicated can 

 perhaps be accounted for by the supposition of natural spread from 

 the original points of introduction. Its presence in Oregon and 

 Washington, however, can hardly have come about in this way. There 

 is apparently no record of its intentional introduction into that area, 

 and a wide area in which the species is not known to occur intervenes 

 between these far Western States and the nearest point of intentional 

 release of it. Its presence in these States apparently must be ac- 

 counted for on the basis of accidental introduction, probably through 

 the agency of commerce. 



IMPORTANCE 



According to Hill and Smith this species ranks fifth in importance 

 as a parasite of the fly in the Middle Atlantic States. Over a period 

 of 10 years it showed an average of only 1.13 percent j^arasitization 

 of the fly, however, with a maximum in any one year of 3.59 percent. 

 These percentages are not sufficiently high to indicate that the species 

 is more than a rather minor factor in the control of the fly. 



TETRASTICHUS CARINATUS Forbes 



(Fig. 32) 



Tetrastichus carinatus Forbes, 111. State Ent. Rpt. (1884) 14: 48, 1885; Rilev. 

 U.S. Natl. Mus. Proc. (1885) 8: 421, 1886; Amer. Nat. 19: 1105, 1885; Amer. 

 Assoc. Adv. Sci. Proc. (1885) 34: 334, 1886; Lindeman, Bui. Soc. Nat. Moscou 

 (2) 1: 185, 1887; Cresson, Synopsis of the families and genera of the Hymenop- 

 tera of America, north of Mexico . . . , p. 245, 1887 : Osborn, U.S.Dept.Agr., 

 Div. Ent. Bui. (n.s.) 16: 28, 37, 1898; Dalla Torre, Catalogus hymenopter- 

 orum . . ., v. 5, p. 12, 1898; Sanderson, Del. Agr. Expt. Sta. Rpt. 12:207, 1901: 

 Ainslie, Ent. Soc. Wash. Proc. 10: 15, 1908; Folsom, 111. Agr. Expt. Sta. Bui. 

 134: 122, 1909; Headlee and Parker, Kans. Agr. Expt. Sta. Bull. 188: 109, 

 1913; Felt, N.Y. State Ent. Rpt. 28 (Mus. Bui. 165) : 39, 1913; Hill and Smith, 



