Adult Reproductive Tract Morphology and Spermatogenesis in the Black Soldier Fly (Diptera: Stratiomyidae)

Abstract

Large-scale production of the black soldier fly [Hermetia illucens (L.) (Diptera: Stratiomyidae)] for use as aquaculture and poultry feed has developed into a global industry. Successful commercialization of the black soldier fly relies on optimizing the production of fecund adults. However, current mass-rearing protocols result in variable production of fertile eggs. To help lay a foundation for a better understanding of factors that may play a role in this variability, the morphology of the black soldier fly male reproductive tract and spermatozoa, associated spermatogenesis process, impact of age on the process, and the female spermatheca morphology were examined with various microscopic techniques (e.g., scanning electron microscope, transition electron microscope, and dissecting scope). The gross morphology of the male reproductive tract and female spermatheca appear to be similar to those found in other brachyceran flies. Male spermatozoa are long (~860 µm overall, ~8 µm head), apparently motile, and possess flagella with a typical 9 + 9 + 2 axoneme triplets. Germ cells go through incomplete mitotic divisions surrounded by somatic cyst cells in the testes. Spermatogenesis appears to be initiated during immature development (cryptocephalic pupa stage). From <24 h to 7 d post-emergence, male aging appeared to impact sperm production.