Tetracycline has no long-term effects on gut physiology and microbiome of the new world screwworm, Cochliomyia hominivorax, which has positive implications for transgenic male-only rearing systems.

Tetracycline repressible (Tet-Off) male-only sexing systems have great potential for improving the efficacy of sterile insect control programs in addition to reducing rearing cost. The relationship between insects and their microbial symbionts, as well as potential physiological stress caused by tetracycline class antibiotics, pose concerns that Tet-Off strains could have reduced fitness in nature. Here, we evaluated the biological performance, midgut microbiome, and midgut transcriptomes of wild-type screwworm, Cochliomyia hominivorax, reared in diet without Tc (control), with Tc (on-Tc), or a pseudo "male-only" condition where offspring of the Tc fed line were reared without Tc (post-Tc), like Tet-Off strains previously developed for this species. Biological performance was not significantly changed by the inclusion of Tc in the diet, and in most cases the flies reared with Tc were generally more fit than lines reared without Tc. The gut microbiome and transcriptome revealed interesting and similar patterns. In both surveys, the greatest changes were between both control and post-Tc treatments and the on-Tc treatment. Very few differences were observed between control and post-Tc treatments, suggesting that there are few negative persistent effects of Tc exposure to fly colonies, and flies revert to their natural state rapidly after the removal of Tc. These results suggest there are limited negative impacts of Tet-Off regulatory systems for use by the C. hominivorax eradication program, and differences observed in Tet-Off strain performance are likely not related to Tc exposure.