40 BULLETIN 640, U. 5. DEPARTMENT OF AGRICULTURE. 



abundance of the fruit fly. To-day no batch of infested fruit can be 

 collected from which fruit-fly parasites can not be reared. 



Onl}' 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 per 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 five 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. 



