Releases of Sterile Screw-Worm Flies in Northern Veracruz, Mexico, Measured by Recovery of Sterile Egg Masses1

Abstract

During 1964 and 1965, aerial releases of sterile screwworm flies, Cochliomyia hominivorax (Coquerel), were made in field tests in northern Veracruz, Mexico, at the rate of 4000 flies per square mile, by using invariable flight lanes 8 and 12 miles apart. The effect was evaluated on the basis of the numbers of sterile egg masses recovered from wounded sheep penned in the area. Although about 70% of the collected egg masses were sterile when populations of wild flies were low, the sterile flies were not effective in preventing wild fly increases when the weather favored their activity. Effective control could not be demonstrated in persistent population centers nor in unisolated populations. However, sterile flies released this far apart when the density of native populations is low may be of value in areas where wild populations are low and scattered for extended periods.