Research On The Prospect Of Insect Agriculture

Planting and animal husbandry production are the main factors causing nitrogen pollution,especially the source of agricultural waste represented by livestock and poultry manure nitrogen will be released to the environment,resulting in the continuous deterioration of human living environment.Black soldier fly larvae（BSFL,Hermetia illucens）bioconversion technology shows great advantages and application potential in improving nitrogen management and achieving nitrogen recovery.However,there are few research reports on the nitrogen conversion mechanism in the BSFL bioconversion system.Clarifying the main factors affecting nitrogen flow is conducive to the improvement of protein production efficiency and the development of insect agriculture represented by black soldier fly.This study aims to investigate the nitrogen response characteristics of BSFL bioconversion system to different media and evaluate the application prospects of insect agriculture represented by black soldier fly,and the main research contents and results are as follows:（1）For feed protein production,three BSFL bioconversion systems for livestock and poultry manure（pig manure,chicken manure and cow manure）were constructed,and a control group without BSFL was set up to investigate the effect of BSFL on nitrogen conversion in livestock and poultry manure.The nitrogen-rich chicken manure BSFL bioconversion system was the most prominent,with the highest protein yield of 4.00±0.30g,and only 1.56±0.11g and 0.94±0.07g of insect protein were harvested in the pig manure and cow manure groups,respectively.In the BSFL bioconversion system of pig manure,chicken manure and cow manure,the cumulative release of ammonia（NH₃）decreased by 31.95%,15.43%and 18.16%compared with the control group,respectively,and there was no significant difference in the cumulative release of nitrous oxide（N₂O）compared with the control group.In the chicken system,the introduction of BSFL increased the abundance of amo A gene in the nitrification pathway and the nar G,nir S,nor B and nos Z genes in the denitrification pathway,and the enhancement effect weakened as the growth rate of BSFL slowed.The emission of N₂O in the BSFL bioconversion system of chicken manure was positively correlated with the amo A gene of the nitrification pathway and the nor B and nos Z genes of the denitrification pathway,and the larval growth rate was positively correlated with the abundance of functional genes of nitrification and denitrification.（2）For edible protein production,a clean chaff medium BSFL bioconversion system was constructed.Using chaff+glucose+water+BSFL as the control group,and the experimental group added different types（ammonium chloride,sodium nitrate and soybean protein）and different doses of nitrogen sources to the control group to investigate the bioconversion ability of BSFL to different nitrogen sources.Under the optimal nitrogen source dosages,the yields of BSFL protein in the ammonium chloride（NH₄⁺）group,sodium nitrate（NO₃^-）group and soybean protein（Org）group reached 2.01±0.09g,2.44±0.06g and 3.36±0.13g,nitrogen use efficiency（NUE）reached 0.69±0.08,0.55±0.03 and 0.32±0.02,respectively.And the cumulative NH₃release was335.9mg,559.3mg and 981.1mg,cumulative N₂O release was 0.54mg,10.36mg and0.16mg,respectively.Org group got the highest protein yield,but the lowest NUE,and NH₃release is the largest;NH₄⁺group got the lowest protein yield,but the highest NUE;NO₃^-group got the largest release of N₂O.BSFL significantly reduced the bacterial richness in the matrix,and the microbial community structure in the matrix of the NO₃^-group and the Org group was similar,while the microbial composition of the NH₄⁺group matrix was significantly different from other groups.On the 6th day of bioconversion,the abundance of Firmicutes in the NH₄⁺group reached 46.8%,which was significantly higher than that in the NO₃^-group and the Org group.On the 12th day of bioconversion,the abundance of Actinobacteriota in the NH₄⁺group reached 83.2%,which was significantly higher than that in the NO₃^-group and the Org group.The growth rate of BSFL in the chaff medium conversion system was mainly negatively correlated with matrix moisture content and conductivity,positively correlated with matrix p H,and extremely positively correlated with the abundance of Brevundimonas.（3）Based on the study of clean inorganic nitrogen（NH₄⁺-N and NO₃^--N）BSFL bioconversion system,the nitrogen use efficiency（NUE）,land use（LU）and greenhouse gas emissions（GHGs）of insect agriculture represented by black soldier fly were calculated,and compared with traditional planting and animal husbandry.The NUE of insect agriculture was 0.52-0.72,which was higher than that of planting（0.22-0.48）and animal husbandry（0.07-0.55）.LU is 1.39-1.54m²/kg DM,which is lower than planting（1.18-12.58 m²/kg DM）and animal husbandry（19.38-467.35m²/kg DM）;GHGs emissions were 5.88-6.59kg CO₂eq/kg DM,which was higher than that of planting（0.27-3.26kg CO₂eq/kg DM）,but still much lower than that of animal husbandry（10.66-211.07kg CO₂eq/kg DM）.The essential amino acid content of BSFL protein can reach 40.19%-42.25%,which is higher than that of plant protein（33.31%-38.18%）,and comparable to animal protein（41.37%-43.48%）.Insect agriculture has a shorter production cycle than planting and animal husbandry,and is not limited by extreme weather and organic nitrogen sources.This study showed that BSFL helped reduce NH₃release in the process of converting livestock and poultry manure to produce feed protein,and larval growth rate was positively correlated with the abundance of nitrification and denitrification functional genes,which indicated that BSFL accelerated the nitrogen conversion process.BSFL can synthesize insect protein using soy protein,NH₄⁺-N and NO₃^--N,but the NUE of BSFL to convert organic nitrogen（soy protein）is too low,resulting in serious nitrogen loss,so the two types of inorganic nitrogen may be more suitable for BSFL-derived edible protein production.BSFL can inhibit the microbial diversity of the substrate and may be mutually beneficial symbiotic with Brevundimonas.In the multi-dimensional comparison of insect agriculture,planting and animal husbandry,the insect agriculture has more advantages.