Nov. 25, 1918 Biology of Fruit-Fly Parasites in Hawaii 463 



taining about 100 females of P. duhius and left until December 2. They 

 were then removed and on December 7 and 8 dissected and carefully 

 examined. Thirty-one contained a dead larva or pupa of D. tryoni on 

 which was feeding a mature larva of P. duhius; 73 contained a dead 

 larva or pupa of O. humilis on which fed a larva of P. duhius; 2 con- 

 tained a dead larva of D. fullawayi on which was a larv^a of P. duhius; 

 22 contained from 3 to 31 larvae of T. gifjardianus, some of which were 

 in each case dead and on which fed a larva of P. duhius; 30 contained 

 decomposed fruit-fly pupae parasitized by P. duhiits alone. Of the re- 

 maining 183 puparia, 46 were unparasitized, 88 were parasitized by only 

 O. humilis, 31 by only D. tryoni, and 18 by only T. gifjardianus. 



Again, on October 23, 50 fruit-fly puparia containing developing 

 larvae of O. humilis and D. tryoni were exposed to attack by G. silvesirii 

 for one day. On October 30 they were placed in a jar containing females 

 of P. duhius and left for two days. They were then opened and ex- 

 amined on November 10 with the following interesting results: Thirty- 

 five contained dead larv^ae of G. silvestrii lying in dead larvae of O. hu- 

 milis or D. tryoni, on the whole of which was feeding in each case a larv^a 

 of P. dubius. 



The relation of the P. duhius to T. gifjardianus is also of interest. 

 Very frequently a puparium containing 15 or 20 larvae or pupas of T. 

 gifjardianus and exposed in the laboratory to attack by P. duhius will 

 yield a normal adult of P. duhius and several normal adults of T. 

 gifjardianus. On November 23 and 24, 83 fruit-fly larvae were para- 

 sitized by T. gifjardianus in the laboratory. The 83 puparia forming 

 from these were then placed with adults of P. duhius and left for three 

 days. On December 8 the puparia were opened and examined. In 23 

 cases examined, from 4 to 20 dead larvae of T. gifjardianus were found, 

 and on these in each case was feeding a mature larva of P. duhius; in 

 30 puparia from i to 10 living pupae of T. gifjardianus occurred together 

 with from 3 to 20 dead larvae of that species upon which were feeding 

 larvae of P. duhius, one in each instance; in the remaining 33 puparia 

 from 7 to 19 individuals of T. gifjardianus were developing in the ab- 

 sence of individuals of P. duhius. 



In conclusion, it should be borne in mind that G. silvestrii is not known 

 to be established in Hawaii as yet, and that P. duhius probably only 

 parasitizes a fraction of i per cent of the fruit-fly puparia in the field, 

 but that the relations between these and the other fruit-fly parasites, as 

 detailed in the foregoing pages, can be expected as a natural sequence if 

 they ultimately adapt themselves to Hawaiian conditions and become 

 thoroughly established. 



