Nov. 25, 1918 Biology of Fruit-Fly Parasites in Hawaii 439 



Although the mature fruit-fly larva is the stage most frequently at- 

 tacked by the parasite, younger larvae are often sucessfully parasitized. 

 On September 15, 191 6, a microscopical examination of the contents of 

 107 fruit-fly larvae in the second instar, removed from fruit collected in 

 Honolulu, gave interesting results. Twenty-four of these contained eggs 

 or larvae of either Diachasma tryoni or Opius hwrnilis. 



The female of Diachasma tryoni oviposits in larvae in fruit after it 

 has fallen to the ground and with equal facility attacks the larvae in the 

 fruit before it falls. The heaviest parasitism, however, probably occurs 

 while the fruit is still on the tree. In March and April, 191 7, a quan- 

 tity of fruit, infested with fruit-fly larvae known to be unparasitized, 

 was placed on the ground beneath fruit trees and left for periods of 

 24 to 48 hours. It was then collected and placed in glass jars. From 

 this fruit 208 individuals of D. tryoni were reared. A total parasitism 

 by D. tryoni of 27.1 per cent was secured during August, September, 

 and October, 1917, from 1,435 fruit-fly puparia coming from fruit col- 

 lected from the trees in Honolulu. From 15,907 fruit-fly puparia secured 

 from fruit collected from the ground during the same months a para- 

 sitism of 3 1. 1 per cent by D. tryoni was obtained. 



Of 83,304 fruit-fly larvae secured in Hawaii during 1916, 13.3 per cent 

 were parasitized by Diachasma tryoni. During 1917, as determined from 

 collections of 72,139 larvae, the parasitism by this species was 20.3 per 

 cent. 



Parasites confined in glass sterilizing tubes closed at one end, plugged 

 with cotton, and kept continuously in partial darkness usually will remain 

 alive and active for about two months. After eight or ten weeks of con- 

 finement the mortality is heavy. Only a few individuals have been kept 

 alive beyond 80 days. Females not permitted to oviposit generally out- 

 live the males. There is one record, however, of a male that lived for 125 

 days. Ovipositing females do not live in confinement much beyond 25 

 days even under the best of care. During May and June, 191 7, 98 females 

 were confined in small screened boxes kept in partial darkness and given 

 material in which to oviposit constantly. Of these, 87 lived from 12 to 

 18 days and only 1 1 lived from 20 to 24 days. These were fed daily with 

 a thin solution of honey and water placed in minute drops upon fresh 

 leaves. Brown sugar, diluted with water in a ratio of i part of sugar to 5 

 of water, is a satisfactory food, though the results of feeding with diluted 

 honey are better. A small portion of crushed apple or other fruit is rel- 

 ished by the parasites. Extract of beef added to the honey solution 

 has been tried with unsatisfactory results. Concentrated honey or sugar 

 solutions are also unsatisfactory. Parasites have been kept in a vigor- 

 ous state longest when given honey diluted with 4 or 5 parts of water 

 varied with a 3- or 4-hour period daily during which nothing but 

 water is given.* Without food and held in bright light, the majority 

 of the adults of this species under observation died in from 50 to 60 hours 

 after emergence. 



' For useful methods of confining parasites see Pembbrton and W11.1.AKO (,4). 



