In a pilot eradication experiment conducted on Rota in 1961-62 by the Division's 

 Hawaii laboratory, failure to adequately overflood the natural population of the oriental 

 fruit fly ( Dacus dors alls Hendel) resulted in failure to achieve eradication. Allowing for 

 some loss in competitiveness of the irradiated flies released, the effective ratio of 

 sterile to fertile insects was probably less than 5 : 1. A marked delay in seasonal 

 buildup of flies was apparent when compared with previous records, but trapping records 

 indicated a trend not unlike that shown in model 4 for the h5^othetical population sub- 

 jected to the release of sterile insects. Failure to achieve the objective in this case was 

 not a failure of the principle of control by the use of sterile insects. The results were in 

 line with those that could have been expected imder the circumstances. Research 

 resources were inadequate to produce the number of sterile flies required in this case. 

 However, the failure emphasized the necessity of assuring an adequate rate of over- 

 flooding of the natural population with sterile insects. Based on this experience, 

 additional experiments using sterile-insect releases for eliminating populations of the 

 melon fly (Dacus cucurbitae Coquillett) and the oriental fruit fly were undertaken under 

 conditions that assured adequate overflooding rates, and under these conditions the 

 method proved highly successful. 



Trends of an Insect Population Subjected to an Integrated Program of Sterile- 

 Insect Releases and Conventional Methods of Control 



When an insect population is too high to manage with sterile releases, even at the 

 lowest level in the normal seasonal cycle, consideration should be given to first reducing 

 the natural population by conventional means to a level that would make it practical to 

 adequately inundate the natural population by the release of sterile insects. Theoretically, 

 this approach offers the greatest potential for employing the sterile-insect-release method 

 for practical control or eradication programs , In the first oriental fruit fly experiment 

 on the Island of Rota already alluded to, it would have been practical without too much 

 cost or effort to substantially reduce the natural population with protein hydrolysate bait 

 sprays or by the use of methyl eugenol for male annihilation before initiating sterile- 

 insect releases. In line with the earlier discussion, these methods would be highly 

 efficient when the population is high, but progressively less efficient when it is low, so 

 that a combination of the chemical control and sterile-insect releases would have been 

 the most practical procedure to follow. 



It is the writer's view that the potentialities of an integrated program involving the 

 use of sterile insects, has not been given due consideration by scientists when estimating 

 the value of sterile insects for the control of any given insect species. It may be 

 desirable, therefore, to consider certain hj^othetical models in an effort to explore the 

 theoretical advantages of the combined approach. One procedure, although not necessar- 

 ily the best one, would be to institute an intensive program of control by conventional 

 methods so as to reduce a high population to levels that could then be managed more 

 economically by the subsequent release of sterile insects. 



