88 BULLETIN 536, IT. S. DEPARTMENT OF AGRICULTURE. 



DlACHASMA TRYONI CAMERON. 

 HISTORY. 



Diachasma tryoni Cameron (Plate XXI, fig. 2) is primarily a para- 

 site of the Queensland fruit fly (Bactrocera tryoni) and was first reared 

 by Brooks and Gurney in New South Wales during 1908, and described 

 as a new species by Cameron in 1911. Of 1,5 75 pupse of Bactrocera 

 tryoni secured by Gurney from 18 different lots of fruits during the 

 period from January, 1910, to February, 1911, 30.2 per cent were 

 parasitized; the highest percentage of parasitized being 52.2 per cent 

 of 136 pupa? secured at Narara during February, 1910. During 

 April, 1913, at Gosford the parasitism equaled 70 per cent. While 

 Diachasma tryoni in Australia attacks principally the Queensland 

 fruit fly, it has been definitely reared there from 

 Ceratitis capitata under field conditions, and the 

 indications are strong that it may attack also the 

 island fruit fly, Trypeta musae Frogg. It was 

 the opinion of Gurney that this parasite might, 

 upon occasion, become a valuable check upon 

 C. capitata. 



While en route to Honolulu from West Africa, 

 Silvestri, aided by Gurney, secured pupa? of Dacus 

 tryoni in New South Wales. From these pupae 

 Silvestri reared adults of Diachasma tryoni, of 

 which he succeeded in introducing at Honolulu 4 

 female and 3 male specimens on May 16, 1913. 

 Silvestri soon found in his rearing experiments in 

 Honolulu that the progeny were largely of the 

 male sex, hence 4 females, with males, were liber- 

 ated June 12 in the Kona coffee district of Hawaii, 

 3 females, with males, on July 4 at Waianae, and 

 9 females, with males, on July 11 in Kona, Hawaii. 

 As all the progeny of the remainder of the material held at the 

 insectary were males, the specimens of this parasite now in Hawaii 

 are the progeny of 24 females liberated during June and July, 1913. 

 The first recovery of Diachasma tryoni was made by Ehrhorn during 

 August, 1914, from C. capitata pupse from the Kona district of 

 Hawaii. During October, 1914, a systematic collection of infested 

 coffee cherries throughout this district proved tryoni to be thoroughly 

 established. Although 3 females were liberated at Waianae, Oahu, 

 on July 4, 1913, no specimens were liberated in and about Honolulu 

 until early in 1915. Yet by October, 1915, this parasite was being 

 reared x in small numbers from C. capitata pupse obtained in various 

 parts of the city. 



1 Back, E. A., and Pemberton. C E., Parasitism among the larvae of the Mediterranean fruit fly 

 ( C. capitata) in Hawaii during 1915. Jour. Econ. Ent., v. 9, 1916, p. 306-311. 



Fig. 21.— Opius humilis: 

 Lateral view of pupa. 

 Greatly enlarged. 

 (Original.) 



