Screwworm Eradication Program

1930s. It was not until 1954-1955, however, that the first successful field test was achieved with the eradication of the primary screwworm Cochliomyia hominivorax on the island of Curacao (Netherlands Antilles). This entailed the mass production of sterile males from gamma-irradiated pupae which were then released to mate with wild females. Eggs resulting from these matings do not hatch, thereby reducing fly populations. Subsequent successes in eradicating C. hominivorax were achieved in the southeastern United States in 1959, in the rest of the United States by 1966, and in Puerto Rico in 1974. Following the establishment of the joint Mexico-United States Commission on Screwworm Eradication in 1972, a cooperative program was begun in 1975 to eliminate C. hominivomx in Mexico as far south as the Isthmus of Tehuantepee. Hundreds of millions of flies were mass-reared weekly in facilities at Mission, TX, and Tuxtla Gutierrez, Chiapas (Mexico), for aerial releases in the targeted areas. By 1985 the screwworm had been successfully eliminated from most of southern Mexico and Central America, with a sterile-male barrier being established at the Darien Gap, the isthmus at the border between Panama and Colombia. Efforts are underway to construct a new mass-rearing fly facility in Panama and to extend the eradication effort into Colombia and other South American countries. In the meantime, sterile males have been successfully used in areas where C. hominivomx has reinvaded former eradication zones and where it has been introduced for the first time. C. hominivoraxw&s detected for the first time in Libya in 1988, for example, where it was eradicated within a few months following the release of sterile males in 1991. For further details on the history of the screwworm eradication program, see Meyer (1996).

Another approach to screwworm control has been the development of an attractant called swormlure that simulates the odor of animal wounds (Cunningham et al., 1992; Snow et al., 1982). This has been combined as a bait with pesticides in a pelletized form that can be applied by aircraft to attract and kill gravid females. Called the Screwworm Adult Suppression System, this approach has been successfully used to complement sterile-male release efforts by killing wild female flies that have not mated with irradiated males.

The best approach to area-wide control of cattle grubs is integrated management programs enlisting the cooperation of all producers in the targeted region. The most effective method to date is use of the systemic, antiparasitic compounds known as avermectins. Unlike traditional systemic insecticides that kill only the migrating larvae of cattle grubs, avermectins are also effective in killing second- and third-instar larvae after they have formed warbles. Sterile-male release technology also has shown promise but is limited by inherent logistic problems in the mass rearing of Hypoderma species for this purpose. By combining the use of systemic compounds and sterile-male releases, cattle grub populations and the associated economic losses have been dramatically reduced in North America through the joint United States—Canada Cattle Grub Project initiated in 1982 (Klein et al., 1990; Kunz et al., 1984). Likewise, significant reductions in cattle grub problems have been achieved in Great Britain and several European countries (Boulard and Thornberry, 1984; Wilson, 1986). Although experimental vaccines against Hypoderma species have been developed, they have not been widely field tested. They may, however, play a greater role in the future as one more component of integrated management programs. For further information on the biology and control of cattle grubs, see Scholl (1993).

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