HORSE-FLIES AND WESTERN AGRICULTURE. 



31 



lateral fringe of bristles on anal segment normal. Ventral fringe on this 

 segment interrupted on median line. Terminal teeth on anal segment nearly 

 equidistant. Lateral teeth only slightly more prominent than the others. 



Described from reared specimen under Bishopp No. 7652, Br. 2, 

 larva of which was collected by J. L. Webb near Topaz, Calif. 



Both larva and pupa described with the aid of a binocular micro- 

 scope. 



CHRYSOPS spp. 



Two or three specimens of the genus Chrysops, known commonly 

 as deer flies, are common in the region covered by this investigation. 

 (PI. IV, F.) They are, however, less important as pests than true 

 horse-flies of the genus Tabanus. They attack horses and men quite 

 readily in the higher altitudes, but do not appear to bother cattle 

 to any great extent. 



The eggs and larvae are rather abundant in Antelope Valley, but 

 for some unexplained reason adults are not found there in the 

 same proportions. Eggs are deposited on vegetation above the 

 water, or sometimes on the leaves of a water plant which lie flat on 

 the water. The larvse are to be found in the mud under the water. 



NATURAL ENEMIES OF TABANIDS. 



PARASITES, 



Hymenopterous parasites reared from egg masses of Tabanus 

 punctifer were identified as Prophanurus emersoni Girault. 8 Prac- 

 tically every T. punctifer egg mass collected was infested. This 

 little parasite was observed crawling over a mass of T. punctifer eggs 

 before the parent female had completed the oviposition. 



The total developmental period of this parasite was determined 

 in three masses. 



Table 6. — Developmental period of Prophanurus emersoni. 



Tabanid egg-mass No. 



Date of 



oviposi- 

 tion of 



tabanid 

 and 



parasite 

 eggs. 



Date 

 unin- 

 fested 



tabanid 

 eggs 



hatched. 



Date 

 parasites 

 began to 

 emerge. 



Incuba- 

 tion 

 period 

 of host. 



Develop- 

 mental 

 period of 

 parasite. 



4093. Br. 1 



Aug. 9 

 9 

 9 



Aug. 23 

 20 

 23 



Sept. 1 

 Aug. 31 

 Sept. 1 



Days. 

 14 

 11 

 14 



Dans. 

 23 



7694. Br-1 



22 



7694. Br- 2 



23 







Egg mass No. 7694 Br. 1, from August 16 to August 20, was in 

 direct sunlight out of doors. This shortened the incubation period 

 of T. punctifer 3 days and the developmental period of the parasite 

 only 1 day. 



Males of this parasite would congregate around the holes from 

 which the females were to emerge, and when the female emerged 

 mating took place immediately. 



The few egg masses of T. phaenops found in nature were not 

 infested. An egg mass of T. phaenops was infested with Pro- 

 phanurus emersoni in captivity. On August 5, 1918, an egg mass 



8 Determination by S. A. Rohwer. 



