This study was conducted to investigated ecological character and life cycle of Black Soldier Fly(BSF), Hermetia illucens, to determine effects of BSF on composing ability to waste-food. The distribution of BSF was defined in all parts of the country in Korea. Its main habitat was found to be areas near cattle sheds, manure sheds, living waste dump grounds, and food waste dump grounds.
Observed characteristics of BSF by developmental stage may be summarized as follows: eggs were a long oval shape of 886.9±19.7 ㎛ in major axis and 190.1±9.7 ㎛ in minor axis; they were 24.0±1.6 ㎍ in
weight. One adult insect laid 1001±247 eggs in quantity; days to hatch from eggs (27℃, 60% R.H) were 81.3±12.5 days. Larvae which were hatched appeared to be close to white and turned into pale yellow as being last instar larva. Last instar larva ranged from 20.7±1.1 mm in size, the length of larval stage was approximately 15~20 days. Pupae exhibited red brown, 19.2±1.1 mm in size; pupal state lasted 15.5±1.4 days for female, 14.7±1.4 days for male, exhibiting the tendency of males having shorter period than females. Adult insects were sized about 13~20 mm and colored black.
Life span of adult insect by developmental period is 5~8 days for the 1st generation (June~July), 7~10 days for the 2nd generation (Aug.~Sept.), and 13~18 days for the 3rd generation (Sept.~Oct.), exhibiting the tendency of females to have longer life span than males. Mating started 2days after emergence and was most active during the 3rd day. Mating mostly occurred between 10:00 and 16:00 during which light intensity is high. Laying eggs started 3 days after emergence and was most frequent during days 4~6. Time of laying eggs during the day was similar to copulation time, showing the highest laying rate between 10:00 and 16:00.
In order to develop artificial indoor rearing techniques, plans for BSF collection and indoor rearing protocol by each growing stage were established. BSF collection was conducted between June and October at 1month intervals. For the imago attractant, calf feed and food waste were most effective; trap installed area located in shady spot compared to sunny place demonstrated higher collection rate; highest collection was obtained in August and September.
As the egg-laying medium for artificial egg collection, calf feed and food waste were most effective; appropriate number of medium inserted into egg-laying net(W*D*H = 4*2*2m) was 8 and adult insects 2000; two inlet showed the highest egg-laying rate. For egg-laying materials, flower foam and wood with holes were used; holes sized 3~5mm in diameter, 7~10mm in depth were most preferred for egg-laying. Larvae raised in 2∼4 head / ㎠ density demonstrated superior practical traits than those raised in overcrowded environment (6∼10 head / ㎠). As an appropriate pupal protection condition, medium (sawdust) should be used to provide a hiding place most appreciated degrees of humidity in sawdust was 20∼40% Adult insects should be used immediately after emergence; however, emergence timing was adjustable with about 10 day after pupation was 93.3%; emergence timing was adjustable with about 10 day flexibility.
In the examination of the ability of BSF to decompose food waste, volume of the food waste decreased by 42.9%, weight 67.6% 5 days after larcal introduction capacity of decomposing food by a single larva was 2.2.±0.8g.
Also, We investigated the biochemical properties of digestive enzymes released from the salivary gland and gut of the black soldier fly. Because the gut extracts of the black soldier fly larvae had high amylase, lipase and protease activities, we suggested that the black soldier fly might belong to the polyphagous insect group. In addition, a strong trypsin-like protease activity was observed in the gut extracts of the black soldier fly larvae. Higher activities of leucine arylamidase, α-galactosidase, β-galactosidase, α-mannosidase and α-fucosidase were observed from the gut extracts of the black soldier fly larvae compared with those of house fly larvae. These findings may explain previous reports that the black soldier fly larvae can digest food wastes and organic materials more efficiently than any other known species of fly.
To investigate the molecular scavenging capabilities of the larvae of Hermetia illucens, two serine proteases (SPs) were cloned and characterized. Multiple sequence alignments and phylogenetic tree analysis of the deduced amino acid sequences of Hi-SP1 and Hi-SP2 were suggested that Hi-SP1 may be a chymotrypsin- and Hi-SP2 may be a trypsin-like protease. Hi-SP1 and Hi-SP2 3-D homology models revealed that a catalytic triad, three disulfide bonds, and a substrate-binding pocket were highly conserved, as would be expected of a SP. E. coli expressed Hi-SP1 and Hi-SP2 showed chymotrypsin or trypsin activities, respectively. Hi-SP2 mRNAs were consistently expressed during larval development. In contrast, the expression of Hi-SP1 mRNA fluctuated between feeding and molting stages and disappeared at the pupal stages. These expression pattern differences suggest that Hi-SP1 may be a larval specific chymotrypsin-like protease involved with food digestion, while Hi-SP2 may be a trypsin-like protease with diverse functions at different stages.