Differential effects on ploidy levels and underreplication of Cochliomyia macellaria as a function of electron beam energy and gamma radiation sources.

Cochliomyia hominivorax (Diptera: Calliphoridae) is an obligate parasitic species and a source of major public health concern as an agent of myiasis in humans, livestock, and wildlife systems, causing millions of dollars in agricultural losses annually. A major approach for screwworm control and eradication is the sterile insect technique (SIT) using gamma radiation. Electron beam (eBeam) radiation is a safer and potentially less expensive alternative ionizing radiation source being explored for SIT. To test this method, late-stage pupae of Cochliomyia macellaria, a sister species of C. hominivorax, were exposed to low energy electron beam (LEEB), high energy electron beam (HEEB), and Cs-137 radiation. Treated pupae were allowed to develop to adulthood, and male flies had their testes dissected and analyzed using flow cytometry to evaluate differences in ploidy impacts of each radiation type. Results indicated that the ploidy and abundance of highly polyploid nuclei, most notably 32C nuclei, significantly increased in flies irradiated with HEEB and Cs-137. Flies treated with Cs-137 also had increased amounts of underreplicated nuclei that were not typically seen in control flies or in flies treated with LEEB or HEEB. Results from a small sample size of frozen C. hominivorax adults treated with similar doses of Co-60 indicated similar trends of increased 32C and underreplicated nuclei, but more sampling is needed to investigate species and/or radiation type effects. These results indicate that eBeam can induce ploidy changes in treated flies and highlight the potential of flow cytometry as a biological dosimetry tool given further testing.