TROPICAL FRUIT-FLY MENACE — CHRISTENSON 443 



Sanitation measures, including the picking up and destruction of 

 infested fruits and vegetables and the bagging of individual fruits 

 to prevent infestation, also produced some benefits. 



Man's attention soon turned toward parasites and predators in the 

 hope that these might reduce tropical fruit-fly mfestations to a toler- 

 able level. Repeated worldwide searches for natural control agents 

 in areas wdiere tropical fruit flies are indigenous revealed many prom- 

 ising species. When these were introduced into areas with unusually 

 serious tropical fruit-fly problems, some became established, but none 

 has reduced infestation to a level where it would no longer be of some 

 concern to those who grow highly susceptible fruits and vegetables 

 for profit. Yet the benefits from partial control by these natural 

 control agents have more than justified the expense of parasite explora- 

 tions and research. A cooperative biological-control program against 

 the oriental fruit fly {Dacus dorsalis Hendel) in Hawaii, in which 

 Federal, State, and private research agencies participated, has been 

 a noteworthy example. 



At the conclusion of World War II the oriental fruit fly was acci- 

 dentally introduced into Hawaii — how, no one know^s exactly. En- 

 tomologists searched throughout the tropical and subtropical w^orld for 

 effective parasites. About CO species were sent to Hawaii, where they 

 were studied under quarantine conditions to make certain that no sec- 

 ondary parasites — these are parasites of parasites — would be intro- 

 duced. Several dozens of the introduced parasites were released, and 

 a dozen or so became established. Some of the new natural control 

 agents were immediately successful, but too often this control was only 

 fleeting. Only one parasite, Opius oophilus Fullaway, a species that 

 attacks both the eggs and young larvae of the oriental fruit fly, has been 

 able to maintain significant sustained effectiveness. Before 0. oophilus 

 was introduced, nearly all fruits of preferred hosts of the oriental 

 fruit fly in Hawaii were infested. The new parasite reduced this 

 infestation by at least half, and the number of fruit-fly maggots in 

 individual infested fruits was much less. The result was the saving 

 of large quantities of fruits and vegetables growing in backyard gar- 

 dens and on farms. With fewer adult fruit flies near transportation 

 centers where they might enter airplanes or ships, there was much less 

 opportunity for these flies to be transported to lush breeding grounds 

 in citrus orchards in continental United States. This was an impor- 

 tant quarantine benefit. 



Fruit growers in continental United States, and most of the people 

 who purchase finiits and vegetables in supermarkets, would not coun- 

 tenance the amount of infestation the introduced parasites still permit 

 in Haw^aii. Nevertheless, we are grateful for the good they have 

 done. There is still hope that someday a completely adequate bio- 

 logical-control complex can be attained. Our growing knowledge of 



