Pathogenic Bacteria of Black Soldier Fly Larvae “Soft Rot” Isolated and Identified from Mass Production Facilities and its Incidence Characteristics

Abstract

The black soldier fly larvae (BSFL) can transform organic waste into high-end proteins, lipids, chitin, biodiesel, and melanin at industrial scale. This species' production capacity is growing but scaling up entails health risks to reared insects. This analysis found that soft rot might impact BSFL development and health in mass production facilities. The pathogenic bacteria GX6 was isolated from industrial soft rot samples and identified to be Paenibacillus thiaminolyticus. The spores had no impact on BSFL growth under regular feeding conditions, but the inclusion of GX6 vegetative cells in medium (1×106 cfu/g) increased 6-day-old BSFL mortality to 29.33% ± 2.05% and inhibited BSFL development. Higher temperature increases BSFL mortality and suppress its growth, whereas higher moisture content in the experimental substrate reduces mortality. When infected BSFL guts were dissected and examined, middle intestine swelled and became transparent. Transmission electron microscopy (TEM) indicated that GX6 destroyed the peritrophic matrix and intestinal microvilli and damaged the intestinal epithelial cells of BSFL gut. The sequencing and analysis of the 16S rRNA gene revealed that the composition of the gut bacteria of BSFL infected with the GX6 strain was significantly different from that of the control group. It was observed that Morganella, Fermentomonas, Perfumeria, and Prowitteria bacteria were more numerous in the intestines of GX6-infected BSFL compared to controls. This study will lay the foundation for the control of soft rot and promote healthy development of the BSFL industry to contribute to organic waste management.

Keywords: black soldier fly, Soft rot, Paenibacillus thiaminolyticus, Mass production, Entomopathogen, Hermetia illucens