292 Journal of Agricultural Research voi. xii, no. 5 



of O. humilis, 6 contained living larvae of D. jullawayi together with dead 

 larvae of O. humilis, i contained a dead larva of D. jullawayi together with 

 a living larv^a of O. humilis, and 90 were unparasitized. Here again is 

 striking evidence of positive suppression of the parasite O. humilis by the 

 other parasites, particularly by D. tryoni. Of the 618 puparia examined, 

 the O. humilis occurred 107 times in combination with a species of Dia- 

 chasma and won the struggle for existence in only 5 cases. 



The foregoing would tend to explain the very noticeable fluctuations 

 in the comparative abundance of the two principal species of parasites 

 at differenct seasons of the year, as shown in Table I. It is seen that the 

 extent of parasitism by Opius humilis is greatly influenced by the abun- 

 dance or scarcity of the parasite Diachasma tryoni, and, as elsewhere 

 discussed, the abundance of this latter parasite in Hawaii is very much 

 dependent upon seasonal conditions. This causes a seasonal rise and 

 fall in the effectiveness of 0. humilis. In the summer and autumn of 

 the year the ascendancy of the D. tryoni causes a great reduction in the 

 abundance of O. humilis. During the winter and spring seasons the 

 reduced activity of the Diachasma permits a rapid increase in parasitism 

 by O. humilis. This is particularly true in the elevated Kona coffee 

 district, where the winter temperatures are somewhat below those about 

 Honolulu. 



The results of the first series of dissections of fruit-fly larvae and puparia 

 on the island of Hawaii in January, 1916, led to further laboratory ex- 

 periments in Honolulu on a comprehensive scale, duplicating as closely 

 as possible the field conditions. Unparasitized fruit-fly lars^ae were ex- 

 posed within fruit to the attack of both Opius humilis and one or both of 

 the species of Diachasma for a few hours. The fruit-fly puparia thus 

 obtained were usually all parasitized, and no loss in time resulted from 

 examinations of unparasitized material. In this manner 393 cases were 

 obtained in which fruit-fly larvae were parasitized by both O. humilis and 

 D. tryoni. In 387 of these the Opius larvae were all killed and the Dia- 

 chasm.a survived. In only 5 of the puparia did the former succeed in 

 overcoming the latter and developing. 



Out of yj cases in which fruit-fly larvae were parasitized by both Opius 

 humilis and Diachasma jullawayi, in only 2 did the Opius develop. 

 In the remaining 75 the Opius larvae were all killed by the Diachasma 

 larvae. 



SUPPRESSION OF OPIUS HUMILIS BY TETRASTICHUS GIFFARDIANUS 



The fruit-fly parasite Tetrastichus gifjardianus Silvestri, a late introduc- 

 tion into Hawaii, has proved decidedly destructive to any of the opiines 

 when occurring in the same fly larvae or puparia with them. This 

 chalcid, seemingly of importance, has, after a two years' trial in Hawaii, 

 given but small promise of accomplishing any perceptible control of the 



