Background
The growing global population increases the demand for protein, while the management of organic waste is becoming more challenging. Alternative protein sources are needed to reduce the negative environmental impact of food production. Lately, the black soldier fly (BSF) has been proposed as an ideal animal protein substitute due to its ability to consume and reduce diverse organic waste, thus solving two problems at the same time. Mass-rearing of BSF depends on flourishing reproduction, which is influenced by environmental and physiological factors. BSF females oviposit egg clutches near decomposing organic matter and conspecific eggs, with studies highlighting the crucial role of microorganisms in oviposition. In this study, we focus on the surface microbiota of the egg and its origin. We investigated if the microbiota are inoculated before, during, or actively after oviposition. For this purpose, we analysed the microbiota in the haemolymph and gut of larvae raised on sterilized and non-sterilized feed, the pupal cell pulp, the wash of the egg-laying apparatus and the eggs directly collected after oviposition, the ovarian eggs and the empty female abdomen, the eggs with contact to adult BSF, and sterilized eggs to assess the stage in BSF development during which the microbial colonization of the egg surface occurs.
Results
Our analysis revealed distinct bacterial profiles across life stages, indicating a shift from larval dominance of Enterobacteriaceae to a dominance of Burkholderiaceae on all analysed eggs. On genus level, larval stages were characterized by Morganella sp., Escherichia sp., and Proteus sp., transitioning later to less diverse communities in egg samples predominated by Burkholderia-Caballeronia-Paraburkholderia sp. While eggs from clutches and directly collected from the ovipositor generated viable offspring, surface sterilized eggs and eggs dissected from the ovary turned out to be nonviable. In microbiological cultivation trials, the established sterilization protocol was shown to be effective in removing viable microorganisms from the egg’s surface.
Conclusion
Our study reveals that while a predominant microbiota persists throughout all life stages, its composition undergoes a progressive transformation during maturation, particularly before oviposition. Gaining deeper insights into egg surface microbiota and the cues guiding oviposition has the potential to boost egg production and simplify mass harvesting of BSF larvae.