Development and evaluation of screwworm, Cochliomyia hominivorax, transgenic sexing strains with embryonic gene promoters for a genetic control program

Authors: Arp, Alex; VARGAS LOWMAN, AIDAMALIA - Universidad De Panama; CONCHA, CAROLINA - Copeg; YAN, YING - University Of Giessen; MARTINEZ, ANDREA - Latin University Of Panama; QUINTERO, GLADYS - US Department Of State; VASQUEZ, MARIO - US Department Of State; SAGEL, AGUSTIN - US Department Of State; SCOTT, MAXWELL - North Carolina State University

Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/6/2025
Publication Date: 11/1/2025
Citation: Arp, A.P., Lowman, A.V., Concha, C., Yan, Y., Martinez, A., Quintero, G., Vazquez, M., Sagel, A., Scott, M.J., 2025. Development and evaluation of screwworm, Cochliomyia hominivorax (Diptera: Calliphoridae), transgenic sexing strains with embryonic gene promoters for a genetic control program. J Econ Entomol. toaf295
DOI: https://doi.org/10.1093/jee/toaf295

Interpretive Summary: The New World screwworm, Cochliomyia hominivorax, was eradicated from North and Central America through the first application of the sterile insect technique. The sterile screwworm adult fly releases were mixed sex, but experience with other flies suggests that releasing only males could be up to five times more effective. To achieve male-only screwworm releases, we developed strains of transgenic screwworm that were expected to be female lethal in the embryonic stage in the absence of doxycycline. All strains were female lethal but doxycycline transfer rescued female offspring if the previous generation was fed diet containing doxycycline too late in larval development, reducing any cost savings associated with female embryo lethality. In mating evaluations one type of strain was less successful mating than others. Overall these strains have potential for use in screwworm eradication programs and our experiments show the importance of proper doxycycline dosages when using these genetic control systems.

Technical Abstract: The New World screwworm, Cochliomyia hominivorax, was eradicated from North and Central America through the first application of the sterile insect technique. The sterile screwworm adult fly releases were mixed sex, but experience with other flies suggests that releasing only males could be up to five times more effective. Here we describe screwworm transgenic sexing strains (TSSs) with expected embryo lethality developed using the Tetracycline-off (Tet-off) system with the Lucilia cuprina nullo (DR6) or C. macellaria CG14427 (DR7) gene promoters and a tTA activated effector to promote female lethality. The TSSs expressed tTA highest in 2-3 h embryos and low in larvae and adults. However, most strains showed high expression in pupae. Evaluation on two doxycycline (Dox) regimens found that inclusion of Dox in the last larval feeding rescued females of the subsequent generation, likely by maternal Dox transfer to embryos. All TSSs produced only males on a reduced Dox feeding regimen but the female lethal period for the DR6 TSS was too late in development to save diet costs. Production parameters were met by all strains in colony, but strains had lower male fly survival than current production strains after removing Dox. In non-competitive mating success trials DR6 strains performed poorly, but DR7 performed equally to production strain males. However, males from all TSSs faired poorly in mating competition tests against production males. Our study highlights the importance of tightly-regulated gene promoters and suitable antibotics feeding schemes for the development and evaluation of TSSs based on Tet-off system.