2 CIRCULAR 18, U. S. DEPARTMENT OF AGRICULTURE 



control of the fly would be to collect the horsefly eggs and place them 

 along the streams in vessels which would allow the parasites to 

 escape but which would retain the fly larvae to be destroyed. This 

 circular reports some biological studies of the egg parasite and ex- 

 perimental work in horsefly control by egg collection and parasite 

 d.ssemination. 



DISTRIBUTION AND HOSTS OF THE PARASITE 



The parasite has been reared from the eggs of Tabanus hyalinipen- 

 nis Hine from the counties of Sutton, Edwards, Kinney, Menard, 

 Kimble, Kerr, Bandera, Keal, Uvalde, Zavalla, Medina, Bexar, 

 Comal, Kendall, Blanco, Gillesp e, Mason, Llano, San Saba, and 

 McCulloch in southwestern Texas. The parasite was found in most, if 

 not all, of these counties before general distributions were made. 

 Webb and Wells 3 reported it as parasitizing practically every egg 

 mass of T. punctifer O. S. at Topaz, Calif. Cameron 4 states that 

 eggs of Chrysops moerens Walker and C . mdtis O. S. were fairly 

 commonly parasitized by Trichogramma minutum (Rile} 7 ) and 

 Phanurus emersoni in western Canada. 



PHYSICAL AND CLIMATOLOGICAL CONDITIONS OF THE PARASITE 

 BREEDING GROUNDS IN SOUTHWESTERN TEXAS 



The contour of the south escarpment of Edwards Plateau may 

 be described as rather rugged. The elevation of the plateau is 

 about 2,300 feet above sea level, and the elevation of the stream 

 beds where they leave the valleys and enter the Gulf plains is about 

 1,000 feet. Some of the peaks and divides near the mouths of the 

 valleys are about 2,000 feet above sea level, and there are many high, 

 rocky cliffs. The parasite has been found to breed at elevations of 

 from 800 to approximately 2,000 feet. The escarpment is cut by 

 narrow valleys from 20 to 60 miles long, with many shorter tribu- 

 taries leading out. Nearly ail of these valleys have permanent 

 springs in the heads, and most of the main valleys have permanent 

 streams, some of considerable size. They all have heavy growths 

 of timber along the streams, and in places there are small swampy 

 areas with dense vegetative growths. The heads of the streams 

 are narrow and are more or less shaded, but in the lower parts of 

 the valleys they spread out over gravel beds 100 or more yards 

 wide ancl are exposed to the sun, since flood waters have stunted 

 the timber growth for some distance from the main channels. 



The climate of this area is semiarid. with hot glimmers, usually 

 dry, and mild winters. During the summer the max? mum tempera- 

 tures are generally near 100° F., the nights are cool, and the mini- 

 mum temperatures are usually about 70°. The minimum tempera- 

 tures during the winters are rarely below 20°. The annua) roinfall 

 at Uvalde lias varied from 12 to 40 inches, with an average of 

 approximately 21 inches. The annual rainfall increases toward 

 the east and diminishes westward. Usually more rain falls durmg 

 the months of May and September than during other months. 



a Webb. J L.. and Wells. R. W. horseflies: biolootes and relation to western 

 agriculture. U. S. Dept. Agr. Bui. 1218, 35 pp.. illus.. 1924 



±C.AMEROX. A. E. BIONOMICS OF THE TABVN'DAE (DIPTERA) OF THE CANADIA> PRAIRIE. 



Bul. Ent. Research 17 (pt. 1) : 1-42, illus., 1926. 



