2 CIRCULAR 10 9, XJ. S. DEPARTMEITT OF AGRICULTURE 



and the chalcid Tetrastichus giffardianus Silvestri were imported^from 

 South Africa, and the braconid Diachasma tryoni Cameron was intro- 

 duced from Austraha. Other parasites were introduced, but the 

 four mentioned were the only ones that became estabHshed. The 

 uniform climate of Hawaii and the constant abundance of host 

 maggots resulted in a rapid dispersal of these parasites, and within 

 three years after liberation they were firmly established on the main 

 islands of the Territor}^ and were parasitizing between 30 and 50 per 

 cent of the fruit-fly larvae. 



Since these parasites became established the Bureau of Entomology 

 of the United States Department of Agriculture has compiled a com- 

 prehensive series of records which show the amount of parasitism 

 accomplished by each species and the degree of infestation of host 

 fruits by the fly. These records have been obtained by m_aking almost 

 daily collections of host fruits about the city of Honolulu and securing 

 from them the maggots as they emerged. These maggots were held 

 in rearing jars and the numbers of emerging flies and parasites care- 

 fully recorded. In this manner the eft'ectiveness of each species of 

 parasite has been determined over monthly and yearly periods since 

 1914 for the various host fruits. The results of these observations 

 up to and including 1921 have already been published (1, 2, 4, 6, 

 8,9,10). 



During the first few years after the parasites were liberated m 

 Hawaii yearly reports of their activities were of much interest. In 

 that period there was considerable yearly variation in the effectiveness 

 of each species and in the total parasitism by all species. Conse- 

 quently, during the years from 1915 to 1921, inclusive, these records 

 for each year were published separately, excepting those for 1919 and 

 1920 which were published together in one paper (9). The records 

 for the last five years of this period, however, show that the work of 

 the parasites has become more or less stabilized and that there is 

 much less variation over yearly periods. Consequently, much of the 

 necessity for yearly reports has disappeared, and a 3-year reporting 

 period has been adopted and put into effect in this circular. It is 

 believed that the reader can get a more thorough and comprehensive 

 idea of the relationship and actual work of these parasites if the 

 information for the period is included in one report instead of three. 



RECORDS OF INFESTATION 



In connection with the recording of parasitism, an attempt has 

 been made to note any increase or decrease in abundance of Ceratitis 

 capitata in the field. In making this attem.pt the following hypothesis 

 was adopted: An increase or decrease in the number of maggots in 

 infested fruits will indicate that there has been an increase or decrease 

 in the number of adult flies. As all fruits collected for records of 

 parasitism were held in the insectary long enough to allow all maggots 

 to emerge, and as records of the numbers of all fruits and of the 

 maggots emerging from them were kept, the average infestation per 

 fruit for each species of host can be computed from these records. 

 Tables 1 and 2 give the residts of these observations and computations. 



