6 
Journal of Agricultural Research 
Vol. XXV, No. I 
Diachasma. In 1917 and 1918 * * * 6 it was greater during two months; and 
in 1919 and 1920, for one month out of each year. The control exerted 
over O. humilis by Diachasma, reducing parasitism by the former as that 
of the latter increases, is clearly shown in Table IV. In 1915 O. humilis 
destroyed 31.5 per cent of all Ceratitis capitata larvae under observation, 
or 83.1 per cent of the total parasitized larvae. In 1920 its parasitism 
was only 9.4 per cent of all larvae, and 18.1 per cent of the total para¬ 
sitized larvae. This great decrease in the numbers of O. humilis over a 
period of six years is due almost entirely to the cannibalistic habits of 
D. tryoni and D. fullawayi. Tetrasiichus giffardianus probably destroys 
small numbers of O. humilis , as well as D. tryoni and D. fullawayi . 
Studies of the interrelations of these parasites 7 show that T. giffardianus , 
which does not resort to cannibalism, is capable of destroying opiine 
parasites occurring in the same host larva, probably by starvation. 
This parasite deposits about 10 eggs at one time in a single fruit-fly larva. 
The larvae hatching from these eggs usually have no more than one 
opiine larva to contend with, and they absorb the food material of the 
host so rapidly that the opiine larva usually dies. Before death, however, 
the opiine larva often destroys many of the T. giffardianus larvae, but 
no instance has been observed where the opiine larva survived, although 
such a case may be possible. Should T . giffardianus continue in numbers 
and effectiveness, it will doubtless cause a decrease in the numbers of 
the opiine parasites; and it will be interesting to note what effect the 
new proportions of parasitism will have on the amount of infestation 
by C. capitata. 
The records of fruit-fly parasitism for 1919 and 1920 have shown 
several interesting facts in connection with the efforts to control the 
Mediterranean fruit fly by introduced parasites. The continued activi¬ 
ties of these parasites during the past six or seven years, and the fact 
that they have destroyed approximately 50 per cent of the fruit flies 
developing during the past four years, have caused a noticeable decrease 
in the infestation of some of the most preferred host fruits of the fly. A 
great check has been exerted on the activities of Opius humilis by the 
two species of Diachasma until, in 1920, it was the least effective of the 
three opiines and parasitized a smaller percentage of larvae than during 
any year since its introduction. Diachasma fullawayi and Tetrastichus 
giffardianus have increased greatly in value, and have proved their ability 
to attack fruit-fly larvae in almost any fruit. While the use of parasites 
does not control the Mediterranean fruit fly in Hawaii, it has met with 
a large degree of success, as compared with other methods of combat¬ 
ing this pest, and has decreased the infestation of many edible fruits to a 
marked extent. 
e Pemberton, C. E., and Willard, H. F. work and parasitism op the mediterranean fruit fey 
in Hawaii during 1917. In Jour. Agr. Research, v. 14, no. 13, p. 605-610. 1918. 
Wieeard, H. F. work and parasitism of the mediterranean fruit FLY IN HAWAII during 191S. 
hi Jour. Agr. Research, v. 18, no. 8, p. 441-446. 1920. Literature cited, p. 446. 
7 Pemberton, C. E., and Wieeard, H. F.. interrelations of fruit-fey parasites in Hawaii. In 
Jour. Agr. Research, v. 12, no. 5, p. 285-296, pi. 10-13. 1918. 
