Klammsteiner, T. | Search bioRxiv

bioRxiv2023

Frass fertilizers from mass-reared insects: species variation, heat treatment effects, and implications for soil application

Insect farming has gained popularity as a resource-efficient and eco-friendly method of managing organic wastes by converting them into high-quality protein, fat, and frass. Insect frass is a powerful organic fertilizer, enriching the soil with essential plant nutrients and enhancing plant defense mechanisms through chitin stimulation. Given the importance of frass commercialization for many insect farmers and the use of increasingly diverse organic wastes as insect feedstock, the need for legal guidelines to enable clean production practices has emerged. The recent introduction of a legal definition for frass and heat treatment requirements by the EU commission marks a significant step towards standardizing its quality. However, frass composition is influenced by numerous factors, and little is known about the processes shaping its nutritional profiles and contributing to its maturation. Here, we analyzed the physicochemical, plant-nutritional, and microbiological properties of black soldier fly, yellow mealworm, and Jamaican field cricket frass from mass-rearing operations and assessed the impact of hygienizing heat treatment. Frass properties varied significantly across insect species, revealing concentrations of plant available nutrients reaching as high as 7000 {micro}g NH4+, 150 {micro}g NO2-NO3--N, and 20 mg P per g of total solids. Heat treatment affected microbial activity by reducing basal respiration and microbial biomass carbon, but also reducing viable counts of pathogenic E. coli and Salmonella sp. In terms of microbiome composition, alpha diversity showed no significant differences between fresh and heat-treated frass samples within each insect species, but significant distinctions were observed across the three insect species. The soil application of frass reactivated and boosted soil microbial activity, suggesting no long-term detrimental effects on microorganisms. These results further highlight the potential of insect frass as nutrient rich organic fertilizer, with promising benefits for soil health and nutrient cycling. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=83 SRC="FIGDIR/small/559882v1_ufig1.gif" ALT="Figure 1"> View larger version (46K): org.highwire.dtl.DTLVardef@1935756org.highwire.dtl.DTLVardef@4af4d6org.highwire.dtl.DTLVardef@1104318org.highwire.dtl.DTLVardef@a4e568_HPS_FORMAT_FIGEXP M_FIG O_FLOATNOGraphical abstract:C_FLOATNO Physicochemical and microbiological assessment of frass from black soldier fly (BSF), yellow mealworm (YMW), and Jamaican field cricket (JFC) and the impact of heat treatment. TS = total solids, VS = volatile solids, TDS = total dissolved solids, BR = basal respiration, Cmic = microbial biomass carbon, MQ = metabolic quotient. n.s.: p > 0.05, *: p <= 0.05, **: p <= 0.01, ***: p <= 0.001, ****: p <= 0.0001, o.o.R. = out of range, b.d.l. = below detection limit. C_FIG

microbiology↗

bioRxiv2022

Decrypting the microbiota on the black soldier fly's (Hermetia illucens L., Diptera: Stratiomyidae) egg surface and their origin during development

The increasing global population leads to a soaring demand for protein for food and feed, and also challenges in organic waste management are growing. All this leads to environmental stress, causing biodiversity loss and an increase in greenhouse gas emissions. Alternative and sustainable animal protein sources are needed to reduce the negative environmental impact of food production. In the last years, the black soldier fly (BSF) has been proposed to substitute animal protein, since BSF may consume and reduce a variety of waste organic matter. Successful industrial rearing of BSF depends on a flourishing reproduction of adults, which is influenced not only by environmental but also by physiological factors. The BSF female oviposits single eggs into clutches close to decomposing organic matter and conspecific eggs. Studies have shown that microbes play a significant role in the oviposition of BSF eggs. In this study, we focus on the surface microbiota of the egg and its origin. We investigated if the microbiota is inoculated before, during, or actively after oviposition. For this purpose, we analysed the microbiota in the larval haemolymph and the gut of larvae raised on sterilized and non-sterilized feed, the pupal cell pulp, the wash of the egg-laying apparatus and the eggs directly collected after oviposition, the ovarian eggs and the empty female abdomen, the eggs with contact to adult BSF, and sterilized eggs. The bacterial communities were identified through 16S rRNA gene sequencing to assess the stage in BSF development during which the microbial colonization of the egg surface occurs. We demonstrated that bacteria differ among life stages resulting in a shift during BSF development from dominance of Enterobacteriaceae during the larval stage to dominance of Burkholderiaceae spp. in all analysed eggs. A predominant microbiota is present before oviposition and persists through all life stages, however, the overall populations structure successively shifts during development. A better understanding of egg surface microbiota and oviposition attractants could significantly increase egg production and facilitate the mass harvesting of BSF larvae. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=125 SRC="FIGDIR/small/520758v1_ufig1.gif" ALT="Figure 1"> View larger version (32K): org.highwire.dtl.DTLVardef@1faf08borg.highwire.dtl.DTLVardef@1c66b02org.highwire.dtl.DTLVardef@19b5658org.highwire.dtl.DTLVardef@141b369_HPS_FORMAT_FIGEXP M_FIG O_FLOATNOGraphical abstract.C_FLOATNO Illustration of the sampling procedure to assess egg surface microbiome of black soldier fly and its origin: Larval fed with unsterile (GU) and sterile (GS) feed and the larval haemolymph of GS (LH), the pupal cell pulp (CP), and from the female adults after mating, a wash of the egg-laying apparatus (WS) and the afterwards placed eggs of the egg-laying apparatus (EA), eggs collected from the ovary (EO) and the empty female abdomen (FA), eggs collected from a fly cage after forced exposure to adults (EC) and sterilized (ES). C_FIG

microbiology↗