Research On The Artificial Diet Water Content Optimization And Enzyme-secreting Bacillus Subtilis Of Black Soldier Fly (hermetia Illucens)

Black soldier fly (Hermetia illucens L.) is an important non-pest insect. Its larvae and prepupae, abundant with protein and fat, can be used as feed for variety of animals, including fish, swine and chicken. Additionally, its larvae has been reported to have promising prospects in manure management system, such as house fly control, manure accumulation reduction and the reduction of Escherichia coli and Salmonella enterica in manure. In this essay, the effects on the selected life-history traits of black soldier fly of diets with different water content were studied in order to optimize the rearing conditions. Ten Bacillus strains with protein and organophosphorus metabolic ability were isolated from the gut and skin of black soldier fly larvae to help this insect to utilize the nutrition of diets. Their effects on the selected life-history traits of black soldier fly reared on sterilized hen manure which was inoculated with these Bacillus were studied. At the same time, the effects of these Bacillus on the nitrogen and phosphorus utilization by black soldier fly larvae were tested.The effects of diet water content on the growth and development of black soldier fly were studied. It was found that reared on 75% and 80% water content diets, the larval weight, prepupal weight and total prepupal harvest of black soldier fly were higher, while development time from egg to prepupae or to adult were longer than those reared on 65% and 70% water content diets.Ten Bacillus strains with protein and organophosphorus metabolic ability were isolated from black soldier fly larval gut and skin. Strain S14, S15, S16, S19 and S20 were from larval gut, and strain T2, T4, T6, T7 and T8 from larval skin. The 16S rDNA sequences of these 10 strains were cloned. BLAST analysis results showed these strains were Bacillus subtilis closely related species. Phylogenetic tree based on the BLAST results with gyrB(gyrase B domain) gene sequences identified these strains all as B. subtilis. Phylogenetic tree based on the gyrB gene sequences of these 10 strains, B. subtilis subsp. subtilis str.168 and strain BCRC 10255 showed these 10 B. sbutlis strains had different phylogenetic relationships at species level.These 10 B. subtilis strains were tested in two separate experiments. In the first round experiment, gut companion strains S14, S15, S16, S19 and a control strain B. natto D1 were employed. They were inoculated to the sterilized hen manure at the concentration of 104cfu/g and 108cfu/g. Larvae reared on sterilized hen manure not treated with the bacteria served as the controls. The results showed that all the treatments inoculated with gut strains not only increased the prepupal weight, total prepupal harvest and larval survivorship, but also the nitrogen and phosphorus mass utility efficiency of manure, in comparison to that of control. The results also showed that the same microbe inoculated at different concentration output similar results. In this experiment, strain S15 inoculated at the concentration of 104cfu/g had the best effects among all the treatments.In the second round experiment, skin-attaching strains T2, T4, T6, T7 and T8 were employed. They were inoculated to the sterilized hen manure at the concentration of 104cfu/g, 106cfu/g and 108cfu/g. Larvae reared on sterilized hen manure not treated with the bacteria served as the controls. The results showed that treatments inoculated with skin-attaching strains not only increased the total prepupal harvest and larval survivorship, but also the nitrogen and phosphorus mass utility efficiency of sterilized hen manure, compared with control. The treatments inoculated with skin-attaching strains did not have a significant influence on the development time from egg to prepupae or to adult, and showed significantly negative effects on the individual prepupal weight, the adult body length and longevity, compared with control. The results showed discrepancy among the three treatments of the same strain. In this experiment, Strain T2 inoculated at the concentration of 104cfu/g had the best effects among all the treatments.