Screwworm Eradication Program Research Articles

Swormlure-2 Baited Traps for Detection of Native Screwworm Flies1

A survey was conducted in 12 south Texas counties from Jan.–Apr. 1976 to evaluate swormlure-2 baited traps for detection of native screwworm flies, Cochliomyia hominivorax (Coquerel). In 6 of the 12 test counties, native screwworms were caught before the 1st screwworm case was confirmed. In 3 of the remaining 6 counties, native screwworm flies were captured within 10 days after the 1st case was confirmed. In the other 3 counties, screwworm cases were reported several weeks prior to the 1st capture of flies. The information provided by this survey was used by program officials in the operation of the ongoing screwworm eradication program.

Toxicity of Some Herbicides to the Screwworm1

Two recent events in the USDA Screwworm Eradication Program created the need to know whether certain herbicides were toxic to Cochliomyia hominivorax (Coquerel): Aircraft previously used to carry herbicides were being considered to distribute sterile screwworms. Also, an unusually high mortality observed among sterile flies packaged for release might have resulted from contact with supplies contaminated by certain herbicides.

A Brief Statistical Review of the United States-Mexico Screw-Worm Eradication Program

The first experiments which showed that native populations of the screw-worm fly, Cochliomyia hominivorax (Coquerel), could be reduced under practical field conditions through the release of laboratory-reared sterilized (irradiated) flies were made on Sanibel and adjacent islands off the coast of Florida in 1952–53 by one of us (G.W.E.) and co-workers (unpublished data). The first actual eradication of the fly was accomplished on the island of Curacao some 64 km off the coast of Venezuela (Baumhover et al. 1955). A more impressive demonstration of the effectiveness of the sterile-male technique was the eradication of the screw-worm fly from the southeastern United States (Knipling 1960, Baumhover 1966). A review of these programs as well as a report on the eradication program in the southwestern United States and Mexico during 1962–65 (Baumhover 1966) included statistics concerning numbers of flies released, screw-worm cases, program costs, losses caused by the fly, and savings resulting from the program's operation. The most recent review of the status of the screw-worm eradication program in the southwest and Mexico was given by Hightower (1970). Our paper deals mainly with areas of infestations, screwworm cases reported, and the numbers of sterile flies released in the United States and Mexico during 1962 through 1969.

Contour Maps of Infestation Incidence Useful in Epizootiology of Screw‐Worms, Cochliomyia Hominivorax (Coquerel)

Data collected during the Screw—Worm Eradication Program in the southwestern United States and northern Mexico provided opportunity for the development of contour maps to show the incidence of larvae of the screw—worm fly, Cochliomyia hominivorax (Coquerel), in animal wounds. An empirical technique was developed for choosing biologically meaningful contours and for actual contour plotting. This approach to the study of population dynamics should be useful in studies of other animals.

Susceptibility of Screw-Worm Larvae and Prepupae to Desiccation

In the search for improved techniques for the mass production of screw-worm flies (Cochliomyia hominivorax (Coquerel)) for irradiation and release in an eradication program, one of the more elusive problems has been mortality of pupae caused by desiccation. It was found that the critical period of susceptibility to desiccation exists during the larval and prepupal stages (0 to 48 hours after larvae leave the rearing medium), and that losses sustained in the past can be attributed primarily to delay in providing protection. Screw-worms exposed as full-grown larvae to 90° F. and 40% R.H. for 48 hours suffered a weight loss of 53.5% and only 19.6% survived, compared with a weight loss of only 24% and 94% survival for controls protected with sand cover and room conditions of 85% R.H. A 24-hour exposure after pupation resulted in 31.9% weight loss and 61.4% survival in contrast to weight loss of only 16.1% and 93.7% survival for the controls. Screw-worms protected for 24 hours after pupation suffered minor losses when transferred to conditions of low humidity. Clarification of this critical period of susceptibility to desiccation should greatly improve handling of screw-worms after larval crawl-off and establish a firm basis for avoiding the serious loss from pupal mortality that occurred during the screw-worm eradication program in the Southeast.

Mass Production of Screw-Worms (Callitroga hominivorax) for the Eradication Program in the Southeastern States

From January 1958 to October 1959 slightly more than 3¾ billion pupae were produced, utilizing approximately 6⅓ million pounds of horse and whale meat, during the screw-worm eradication program conducted in the Southeastern States, by the procedures described. The number of grams of eggs obtained from the stock colony and the grams required to meet the weekly fly production quota; the amount of horse and whale meat utilized in producing the minimum of 50 million flies weekly required for field releases; and the number of pupae produced in relation to the number of flies released are shown graphically.