Readdressing methods for evaluating New World screwworm (Diptera: Calliphoridae) strain performance

For the sterile insect technique to successfully control New World Screwworm (NWS), Cochliomyia hominivorax (Coquerel, 1858), released sterile males must be healthy and reproductively competitive with wild populations. In mass-rearing, daily evaluations of developmental and physical metrics are used to evaluate production efficiency, output, and to identify problems with production processes. These observations can detect major strain or production issues, but they may not be sufficient to evaluate how a strain will perform in the field. Here we evaluate novel mating assays, locomotor activity monitors, and flight mills to assess strain performance. Standard production parameters and a non-competitive mating assay were unable to identify differences between outbreak and production strains. When placed in open choice mating tests, the outbreak strain mated with nearly double the number of females as the production strain, implying production males may have reduced mating success when used in sterile releases. Only slight differences were observed in the temporal ("circadian") locomotor activity between males, but outbreak strain females were more active than outbreak males and the previous production strain males and females. In flight mills tests the outbreak-based production strain flew farther on average than the previous production strain and data showed that flight ability was not strongly correlated to fly physical parameters. Overall, our novel tests were able to detect differences in strain quality that were not apparent in the physical measurements or tests typically used to evaluate strains in production.