Trials on variants of the Sterile Insect Technique (SIT) for suppression of populations of the Queensland fruit fly in small towns neighbouring a quarantine (exclusion) zone

Abstract

Seven small unquarantined towns in the central western district of New South Wales were used to compare variants of the sterile insect technique with respect to their suitability for suppression of populations of the Queensland fruit fly, Bactrocera tryoni (Froggatt). Two towns were treated with weekly releases of immature sterile flies at rates varying from 48 000 to 115 000 sterile males per km2. Evidence for suppression was poor (from comparison with 2� untreated towns) and the ratio of sterile to wild flies caught in monitoring traps never exceeded 80 : 1 in the last 4�weeks of any season or 40 : 1 during other parts of any season. However, the recapture rates of the sterile flies and estimates of their survival rates were often as good as the best that have been reported previously. Two other towns were treated with weekly releases of mature flies at rates of 5000–12 000 sterile males per km2. The recapture rates and estimates of survival rates of flies released when mature were unexpectedly low and the ratios of sterile to wild flies were often less than 1 : 1 and never exceeded 12 : 1. The results are discussed in terms of the relatively harsh climate of these towns (located in a region of average annual rainfall of 450–600 mm) and lack of quarantine.