I04 Journal of Agricultural Research voi. xn. no. a 



established are contributing toward a control of the fruit fly. Such data 

 not only indicate the extent of fruit infestation from various localities, 

 but also the amount of parasitism among the larvae from month to month 

 and the seasonal efficiency of each parasite. 



Seasonal diflferences in the value and prolificness of certain species of 

 the introduced parasites have been most striking. This is suggested by 

 an examination of any of the parasite notes from almost any locality 

 and by a comparison of emergences of different species for each month 

 of the year. But most convincing proof that seasonal differences exist 

 is obtained by the inspection of records from fruit collected from the same 

 localities month by month. Some species of trees in Hawaii bear fruit, 

 normally a host of the fruit fly, almost continuously throughout the year. 

 The systematic collection of fruit from such trees and the filing of exact 

 data bearing on the extent of parasitism of fruit-fly larvae secured from 

 such individual trees throughout the year have thrown most light upon 

 the seasonal values of the different parasites. 



Mention of possible fluctuations in the abundance of different species 

 has already been made.^ The work of 191 6, wherein it has been possible 

 to concentrate parasites in fruit collections from individual trees,, has 

 most impressively shown the rise of the parasite Diachasma tryoni 

 Cameron in the summer and fall of the year and its certain decline during 

 the winter and particularly the spring months. Changes in temperature, 

 of no great magnitude, alone seem responsible for this. The parasite 

 Opius humilis Silvestri, more hardy and prolific than any of the other 

 introduced species, has been overshadowed by the other species, partic- 

 ularly by D. tryoni, and has had its seasonal rise and fall directly the 

 reverse and entirely dependent upon the rise and fall of this species of 

 Diachasrha. The slight seasonal changes have little visible effect upon 

 the activities of Opius humilis, however, for in the winter and spring, 

 with the decrease in abundance of D. tryoni, it rapidly ascends and be- 

 comes the most effective check upon the fruit fly (Table III). These 

 interrelations are treated elsewhere by the writers. 



The problem of control of the fruit fly in Hawaii through parasites is 

 only partially solved. The four species already established are accom- 

 plishing a certain control, particularly in the coffee districts, but a casual 

 survey of the extent of infestation of most host fruits as shown in Table I 

 will convince one of the continued destructiveness of this pest in Hawaii. 

 An average parasitism of 40 per cent of all of the larvae developing is, 

 numerically considered, of much importance; but from the standpoint 

 of the practical needs of the horticulturist it brings little relief. 



> Back, E. A., and Pemberton, C. E. parasitism among the larv.b of the mediterranean fruit 

 Fi,y (c. capitata) in Hawaii in 1915. /« Jour. Econ. Ent., v. 9, no. 2, p. 306-311. 1916. 



