Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/28/2003
Publication Date: 10/1/2004
Citation: Rendon, P., Mcinnis, D.O., Lance, D.R., Stewart, J. 2004. Medfly (diptera: tephritidae) genetic sexing: large-scale field comparison of males-only and bisexual sterile fly releases in guatemala. Journal of Economic Entomology. 97: 1547-1553.
Interpretive Summary: Quality improvements in the mating efficiency of sterile flies in SIT programs is a very high priority for national and international program officials. The development of genetic sexing strains, in which males can be separated from females genetically, can produce all-male fly release strains in SIT programs. Preliminary tests in field cages or small-scale release areas showed that releases of all males was several times better than the normal bisexual releases, in that the target wild population was controlled faster and to a higher degree with all-male flies. However, a large-scale demonstration of all-male releases had not been performed until we conducted such a test during 1995-1997 in Guatemala. The results of three years of releases in separate evaluations showed the dramatic result of a several-fold advantage of all-male releases, as measured by the level of induced egg sterility in the wild populations of medfly. Significant levels of sterility were obtained in the males-only release zone at sterile : wild fly ratios of 100:1, while in the control zone of bisexual( male/female) sterile flies, very little sterility was induced even at very high sterile : wild fly ratios ( > 1,000:1).
Technical Abstract: The effect of releases of bisexual (males and female) and unisexual (male only) sterilized medflies was compared in three large field evaluations over a 3-year period (1995 - 1997) in southwestern Guatemala. The two strains tested were a genetic sexing strain, Vienna-4/Tol-94, carrying the temperature sensitive tsl gene to eliminate females in the egg stage, and the standard bisexual Petapa strain. Flies were mass-reared, sterilized by irradiation as pupae, shipped to a field center, and release by air as young adults over 2 km x 2 km core areas in the centers of separate 6 km x 6 km test plots. Strain performance was monitored weekly by trapping sterile and wild male adults in core and buffer areas, and by collecting eggs from coffee berries to determine induced sterility. Results indicated a several-fold advantage for the males-only strain as measured by the level of induced sterility, especially at the very high release ratios of 100:1 recorded in 1997. During that final test year, sterile-fly release rates were increased to provide high sterile:wild (S:W) fly ratios in the field, and egg sterility reached levels in excess of 70% in plots were the male-only strain was used. However, in the plots where the bisexual strain was released, induced sterility only reached 12% in spite of S:W ratios above 1,000:1.