We need more precise quantitative information on the natural population density, 

 especially during periods of scarcity, for such insects as the tobacco budworm ( Heliothis 

 virescens (F.))» the corn earworm, cabbage looper, pink bollworm, the southwestern 

 corn borer ( Zeadiatraea grandiosella (Dyar)), house flies, and certain mosquitoes, just 

 to name a few. Techniques such as the Lincoln index have been developed for making 

 reasonably good estimates. Radio-tagged and released screw-worm flies were employed 

 in early work conducted by R. C. Bushland, A. H. Baumhover, and their associates to 

 obtain information on the natural population density of this insect. Various colored 

 marking materials can be used to advantage. L. F. Steiner and associates of the Hawaii 

 fruit fly laboratory have conducted much research on population density estimates of 

 tropical fruit flies. By releasing a given number of marked flies, in a given area, over 

 a certain period of time, and then determining the ratio of unmarked to marked insects 

 recaptured in male lure traps, good estimates have been made. F. R. Lawson and 

 associates have followed similar procedures in estimating the natural population density 

 of the tobacco homworm moth. Light traps were used for recapture of marked moths 

 and for the capture of moths of the natural population. By emplo3dng such procedures it 

 should be possible to make good estimates of the natural population density of many other 

 insects. 



Importance of Information on Current Losses and Current 

 Control Costs in Estimating the Practicability of 

 Rearing Insects for Release 



In the final analysis, the practicability of utilizing a new method for complete popu- 

 lation control of a pest will depend on the cost of such method in relation to current 

 control costs, plus the losses caused by the pest, or its importance as a pest of man, or 

 vector of human diseases. Consideration of these factors is essential in appraising the 

 practicability of using the sterile-insect-release method, or any other method, for 

 control or eradication. A few examples might be cited to emphasize this point. 



Tsetse flies in Africa are of major importance as vectors of trypanosomiasis in 

 livestock and man. Yet, based on the judgment of authorities in this field, economics 

 will not justify eradication efforts in many areas. The current cost of eradication is too 

 high in relation to the current economic returns that will accrue to agriculture to warrant 

 eradication expenditures. The cost of methods now employed varies considerably in 

 different situations, and constant improvements are being made. However, as a yard- 

 stick, the writer has used a cost figure of $500 per square mile as a reasonably valid 

 estimate of current costs for eradication. Tsetse fly experts and economists in Africa 

 consider this cost justifiable at present, from an agricultural viewpoint, in certain areas, 

 but not in others. Any reasonable chance of reducing current eradication costs by using 

 the sterile-release method would seem to justify a determined research effort. The 

 relatively high current costs for tsetse fly eradication, and estimates of natural popu- 

 lation densities of the insects in various situations, were the two major elements 

 considered by the writer in appraising the possible role that sterile-male releases might 

 play in tsetse fly eradication efforts. 



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