Development of Sustainable Strategies for the Production of Insect Protein by Hermetia illucens

Abstract

Insects are not only on the menu of wild animals, but have been consumed by humans, their ancestors and related primates for thousands of years. Insects are suitable for sustainable commercial mass production due to their ability to convert side streams of agriculture and food industry with low nutritional properties into valuable insect protein in a short period. With regard to projections of global population growth and the associated rapid increase in protein demand, insects are coming into the focus of science as an alternative protein source for food and feed. Although previous studies have focused on the optimization of black soldier fly (Hermetia illucens, BSF) larval breeding conditions, little is known about light-dependent adult development. Since the mating only takes place under adequate lighting, artificial illumination systems are indispensable especially at latitudes with short days in autumn and winter months. In this thesis, the effect of broad spectrum (350–800 nm) light-emitting diode panels with color temperatures of 3,000, 4,000, and 6,500 K on the oviposition was examined. Mating occurred under all light panels, resulting in comparable preoviposition periods (16.8 ± 0.3 d) and the subsequent deposition of fertilized egg clutches. The oviposition period and performance were not affected by color temperature, ranging between 2–15 d and 4.7 ± 0.5 mg eggs per female, respectively. In contrast, oviposition peaked after 1–7 d and was positively correlated with increasing color temperature (r = 0.61). The intestinal microbiota of BSF larvae contributes heavily to dietary breakdown and enables the larvae to utilize a variety of organic substrates including fiber-rich plant-derived side streams. Therefore, BSF larvae were reared on palm kernel meal (PKM) and their bacterial and fungal gut communities were characterized in a culture-dependent approach. A total of 93 isolates could be generated, of which 74% belong to the bacterial phyla Actinobacteria, Bacteroidetes, Firmicutes, and Proteobacteria. Consistent with further studies and regardless of the diet composition and the rearing conditions, Klebsiella, Enterococcus and Sphingobacterium were identified as part of the larval core microbiome. With 75%, a majority of fungal isolates belonged to the phylum Ascomycota, followed by Basidiomycota, and Mucoromycota. Furthermore, representatives of the taxa Cellulomonas, Enterococcus, Pichia, and Fusarium have frequently been described to degrade lignocelluloses and they could accordingly have contributed to increase the digestibility of PKM. All isolates were subsequently screened for entomopathogenicity and putative candidates injected intracoelomally. The injection assay revealed that Alcaligenes faecalis caused no, Diutina rugosa weak, Microbacterium thalassium moderate, and Pseudomonas aeruginosa and Klebsiella pneumoniae high lethality. Fusarium solani injection resulted in 100% lethality one day post-infection. In addition, a combination of PKM with empty fruit bunches (EFB) – another side stream of palm oil production – was evaluated for its suitability as feed for BSF larvae. It was shown that larvae whose feed was fermentatively pretreated with Bjerkandera adusta (BAD) developed significantly faster and reached a higher final weight than those reared on the non-fermented reference (NFR) feed or on feed fermented with Irpex consors or Marasmius palmivorus. Amplicon sequencing revealed major differences in the larval gut microbiomes. While the NFR group was dominated by facultatively anaerobic, cellulolytic Enterobacteriaceae, BAD guts favored obligate anaerobic, cellulolytic taxa like Ruminococcaceae and Lachnospiraceae. Thus, B. adusta pretreatment led to lignin degradation and mycelia accumulation, resulting in a microbial adaptation that may have further enhanced substrate digestibility through cellulolytic breakdown of fiber residues. In summary, the results of this thesis underline the tremendous adaptability and bioconversion capacity of BSF larvae. The optimization of artificial lighting systems enables year-round breeding of BSF outside of (sub-) tropical regions with heavily fluctuating day lengths. Due to the fermentative pretreatment, not only PKM, but also the less nutritious EFB could be utilized by BSF larvae and upcycled into valuable insect protein. The intestinal microbiome seems to play an essential role in this process and general aspects of insect health.