Effects of Disinfectants on Larval Growth and Gut Microbial Communities of Black Soldier Fly Larvae

SIMPLE SUMMARY: Swine manure is a significant source of agricultural organic waste, and in recent years, it has been shown that black soldier fly (BSF), Hermetia illucens (L.), (Diptera: Stratiomyidae), is effective at treating manures or compounds based on them. African swine fever virus (ASFV) infections have significantly modified the preventative procedure, including the disinfection of manure with various disinfectants, since 2018 when they first became a serious issue in the Chinese swine production industry. However, there is not any research discussing the influences of disinfectants in manures on black soldier fly larvae (BSFL). Therefore, this study examined the effects of the disinfectants contained in pig manure on the growth of BSFL and the reduction of waste. Additionally, the disinfectants might not only eliminate important pathogens but also alter the microbial composition of the gut of the larvae; thus, investigations of the intestinal bacterial communities of the BSFL-fed manures, which were mixed with various disinfectants, were conducted. These findings will be helpful in providing a better treatment of swine manures with BSFL. ABSTRACT: The use of the black soldier fly has been demonstrated to be effective in the treatment of swine manure. Since the outbreaks of ASFV, prevention procedures, including manure disinfection, have changed dramatically. Glutaraldehyde (GA) and potassium peroxymonosulfate (PPMS) have been shown to be effective in the prevention of this pathogen and are thus widely used in the disinfection of swine manures, etc. However, research on the effects of disinfectants in manures on the growth of BSFL and gut microbiota is scarce. The goal of this study was to determine the effects of GA and PPMS on BSFL growth, manure reduction, and gut microbiota. In triplicate, 100 larvae were inoculated in 100 g of each type of manure compound (manure containing 1% GA treatment (GT1), manure containing 0.5% GA treatment (GT2), manure containing 1% PPMS treatment (PT1), manure containing 0.5% PPMS treatment (PT2), and manure without disinfectant (control)). After calculating the larval weight and waste reduction, the larval gut was extracted and used to determine the microbial composition. According to the results, the dry weights of the larvae fed PT1–2 (PT1: 86.7 ± 4.2 mg and PT2: 85.3 ± 1.3 mg) were significantly higher than those of the larvae fed GT1–2 (GT1: 72.5 ± 2.1 mg and GT2: 70 ± 2.8 mg) and the control (64.2 ± 5.8 mg). There was a 2.8–4.03% higher waste reduction in PT1–2 than in the control, and the waste reduction in GT1–2 was 7.17–7.87% lower than that in the control. In a gut microbiota analysis, two new genera (Fluviicola and Fusobacterium) were discovered in PT1–2 when compared to GT1–2 and the control. Furthermore, the disinfectants did not reduce the diversity of the microbial community; rather, Shannon indices revealed that the diversities of GT1–2 (GT1: 1.924 ± 0.015; GT2: 1.944 ± 0.016) and PT1 (1.861 ± 0.016) were higher than those of the control (1.738 ± 0.015). Finally, it was found that both disinfectants in swine manures at concentrations of 1% and 0.5% may be beneficial to the complexity and cooperation of BSFL gut microbiota, according to an analysis of microbial interactions.