40 BULLETIN 640, U. S. DEPAETMENT OF AGEICULTTTBE, 
abundance of the fruit fly. To-day no batch of infested fruit can be 
collected from which fruit-fly parasites can not be reared. 
Only a beginning has been made in determining the effectiveness 
of parasites as a control factor against the fruit fly in Hawaii. The 
rapidity of establishment and the increase of the parasites have been 
very gratifying, yet the data already published recording the per- 
centages of parasitism during the years. 1914, 1915, and 1916 indicate 
that while parasitism in thin-meated fruits, such as coffee (see (fig. 30), 
may be consistently very high, in thicker fruits, like the orange, it is 
consistently very low. Thus the parasitism among larvae developing in 
coffee may range between 90 and 100 per cent, while that among larvae 
of the Chinese orange is more likely to range from almost nothing 
to 30 j)er cent. High parasitism among larvae in such fruits as coffee 
is due to the fact that the larvae are within reach of the parasite. 
On the other hand, the larvae within such fruits as the orange may 
feed about the seeds and therefore remain safe from attack so long 
as they stay at the core, and are subject to attacks only when they 
come to the surface of the fruit. 
Since adult fruit flies can live many months and lay eggs quite 
regularly, they have been able, with the aid of the unprecedented vari- 
ety and abundance of host fruits in Hawaii, thus far to keep such an 
ascendancy over their parasites that they cause the infestation of 
practically all fruits ripening. It would appear that unless effective 
pupal and egg parasites are introduced, or more care is given to the 
elimination of host fruits which more thoroughly protect the larvae 
from parasite attack, or to the planting of fruits which make possible 
the reproduction of large numbers of parasites, little practical value 
will result from the work of the parasites from the standpoint of ren- 
dering host fruits free from attack. 
Though it seems evident that the favored host fruits will always be 
well infested if present cultural conditions continue, it is hoped 
that the efficiency of the parasites may be sufficiently enhanced 
to free from attack such fruits as the avocado and the better varieties 
of mangoes. In Kona, Hawaii, where the percentage of parasitism 
in coffee cherries (see fig. 30) has been phenomenally high for three 
years, it has not been high enough to free more than an occasional 
cherry from attack. The control exerted by parasites has, however, 
effected a benefit to coffee growers which probably already has repaid 
the Territory of Hawaii for all money expended in the introduction 
of parasites. 
The general effectiveness of control by parasites can be increased 
best by the discovery and introduction of a good egg parasite. 
