A transgenic male-only strain of the New World screwworm for an improved control program using the sterile insect technique

Authors: CONCHA, CAROLINA - Us Embassy, Panama; PALAVESAM, AZHAHIANAMBI - Former ARS Employee; Guerrero, Felicito; SAGEL, AGUSTIN - Us Embassy, Panama; LI, FANG - North Carolina State University; PARDO, TRINIDAD - Us Embassy, Panama; HERNANDEZ, YILLIAN - Us Embassy, Panama; QUINTERO, GLADYS - Us Embassy, Panama; VASQUEZ, MARIO - Us Embassy, Panama; Phillips, Pamela; MCMILLAN, W. OWEN - Smithsonian Tropical Research; Skoda, Steven; SCOTT, MAXWELL - North Carolina State University

Submitted to: Proceedings of the Royal Society of London B
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/10/2016
Publication Date: 8/30/2016
Citation: Concha, C., Palavesam, A., Guerrero, F., Sagel, A., Li, F., Pardo, T., Hernandez, Y., Quintero, G., Vasquez, M., Phillips, P.L., McMillan, W., Skoda, S.R., Scott, M.J. 2016. A transgenic male-only strain of the New World screwworm for an improved control program using the sterile insect technique. Proceedings of the Royal Society of London B. 14:72.

Interpretive Summary: The New World screwworm (NWS) is a devastating pest that causes great economic losses to the livestock industry. A historic, 60-year eradication program succeeded in eliminating it from North and Central America with the Sterile Insect Technique (SIT). Presently, millions of male and female NWS are regularly mass reared, sterilized and released along the Panama-Colombia border to prevent re-introduction from South America. The Program would benefit from a male-only strain to increase its efficiency of population suppression and reduce overall costs. The first transgenic, male-only lines of NWS have now been developed and evaluated. Several lines produce only males when raised on diet that lacked tetracycline. Most of these male-only lines show production fitness parameters that are comparable to the currently mass reared strain. Males from some of the lines show high levels of sexual aggression and mating competitiveness, which are important parameters in the field. To facilitate the regulatory evaluation, we investigated longevity at cooler temperatures and outcrossing potential, two risks that have been identified for field testing of transgenic insects. We found that the transgenic lines do not live longer than the wild type strain nor can they outcross with its closest relative. One line has been selected for potential mass rearing and an application is pending for an open field test of sterile, transgenic males in Panama. Therefore, a major long-term goal of rearing male-only strains of this insect for SIT has been achieved.

Technical Abstract: The New World screwworm (NWS), Cochliomyia hominivorax, is a devastating pest of livestock endemic to sub-tropical and tropical regions of the Western Hemisphere. The larvae feed on the tissue of living animals, including man, and can cause death if untreated. Over 60 years ago the sterile insect technique (SIT) was developed with the aim of eradicating this pest, initially from Florida but subsequently from all of North and Central America. From the outset it was appreciated that SIT would be more efficient if only sterile males were released in the field, but this was not possible until now. Here we report the development and evaluation of the first sexing strain of C. hominivorax that produces only males when raised on diet without tetracycline. The transgenic lines possess a tetracycline repressible female-lethal genetic system. Ten of these lines show high female lethality at the late larval/pupal stages and two of them present dominant female lethality. Most of the lines were comparable to the wild type parental strain in several fitness parameters that are relevant to mass rearing in a production plant. Further, three lines performed well in male aggressiveness and male competition assays, suggesting they would be sexually competitive in the field. Consequently, two transgenic lines have been selected for evaluation under mass rearing conditions. A sexing strain will reduce production costs for the existing eradication program and provide more efficient population suppression, which should make a genetic control program more economical in regions were C. hominivorax remains endemic.