Effects of temperature and diet on black soldier fly, Hermetia illucens (L.) (Diptera: Stratiomyidae), development

Biowaste treatment using black soldier fly larvae: Effect of substrate macronutrients on process performance

Black soldier fly larvae (BSFL) process is emerging as a promising alternative for the treatment of biowaste. Process performance (such as survival rate - SR and waste reduction efficiency - RE) depends on several factors (e.g. nutritional quality of the substrate) which need to be controlled. The nutritional quality of the substrate can be related to the overall concentration and relative abundance of dominant macronutrients, such as proteins (P), non-fibre carbohydrates (NFC), and lipids (L). Assessing how these substrate quality parameters influence the process performance is fundamental to determining the suitability of a given substrate to be treated by using BSFL and to optimise the process performance. The aim of this study was to gather, integrate, and elaborate published literature to present a comprehensive understanding of how the nutritional substrate quality, impact the process performance in terms of RE and SR. A systematic literature review was conducted by using the PRISMA methodology. The results were graphically elaborated to obtain a simple tool useful for a rapid prediction of the individual substrate suitability to BSFL process and for the evaluation of optimal mixture of different substrates to achieve desired outcomes. A good nutritional quality of substrate (when SR>80% and RE>40%) can be generally identified based on the relative abundance of macronutrients (XP, XNFC, and XL), when XL < 0.6, XP > 0.05, and when XP > 0.5 if XNFC>0.2. Additionally, when XP ranges between 0.05 and 0.15 a good quality substrate occurs if XNFC > XL.

Bioconversion of Poultry Litter into Insect Meal and Organic Frasstilizer Using Black Soldier Fly Larvae as a Circular Economy Model for the Poultry Industry: A Review

Poultry litter waste management poses a significant global challenge, attributed to its characteristics (odorous, organic, pathogenic, attracting flies). Conventional approaches to managing poultry litter involve composting, biogas generation, or direct field application. Recently, there has been a surge of interest in a novel technology that involves the bioconversion of organic waste utilizing insects (known as entomoremediation), particularly focusing on black soldier fly larvae (BSFL), and has demonstrated successful transformation of various organic waste materials into insect meal and frass (referred to as organic frasstilizer). Black soldier flies have the capacity to consume any organic waste material (ranging from livestock litter, food scraps, fruit and vegetable residues, sewage, sludge, municipal solid waste, carcasses, and defatted seed meal) and convert it into valuable BSFL insect meal (suitable for animal feed) and frass (serving as an organic fertilizer). The bioconversion of poultry litter by black soldier flies offers numerous advantages over traditional methods, notably in terms of reduced land and water requirements, lower emissions, cost-effectiveness, swift processing, and the production of both animal feeds and organic fertilizers. This review focuses on the existing knowledge of BSFL, their potential in bioconverting poultry litter into BSFL meal and frass, and the utilization of BSFL in poultry nutrition, emphasizing the necessity for further innovation to enhance this sustainable circular economy approach.

Deeper insight into the storage time of food waste on black soldier fly larvae growth and nutritive value: Interactions of substrate and gut microorganisms

Biological treatment of food waste (FW) by black soldier fly larvae (BSFL) is considered as an effective management strategy. The composition and concentrations of nutrients in FW change during its storage and transport period, which potentially affect the FW conversion and BSFL growth. The present study systematically investigated the effect of different storage times (i.e., 0-15 d) on FW characteristics and its substantial influence on the BSFL growth. Results showed that the highest larvae weight of 282 mg and the shortest growth time of 14 days were achieved at the group of FW stored for 15 days, but shorter storage time (i.e., 2-7 d) had adverse effect on BSFL growth. Short storage time (i.e., 2-4 d) improved protein content of BSFL biomass and prolonged storage time (i.e., 7-10 d) led to the accumulation of fat content. The changes of substrate characteristics and indigenous microorganisms via FW storage time were the main reasons for BSFL growth difference. Lactic acid (LA) accumulation (i.e., 19.84 g/L) in FW storage for 7 days significantly limited the BSFL growth, leading to lowest larvae weight. Both the substrate and BSFL gut contained same bacterial communities (e.g., Klebsiella and Proteus), which exhibited similar change trend with the prolonged storage time. The transfer of Clostridioides from substrate to BSFL gut promoted nutrients digestion and intestinal flora balance with the FW stored for 15 days. Pathogens (e.g., Acinetobacter) in BSFL gut feeding with FW storage time of 7 days led to the decreased digestive function, consistent with the lowest larvae weight. Overall, shorter storage time (i.e., 2-7 d) inhibited the BSFL digestive function and growth performance, while the balance of the substrate nutrients and intestinal flora promoted the BSFL growth when using the FW stored for 15 days.

Comparison of Growth and Composition of Black Soldier Fly (Hermetia illucens L.) Larvae Reared on Sugarcane By-Products and Other Substrates

Black soldier fly larvae (BSFL) can convert organic waste into high-quality biomass. In this study, we tested the potential of sugarcane by-products as a food source for BSFL and compared larval development and nutritional value with some other organic substrates. Seven different substrates were used, including carrot pomace (C), carrot pomace and leftover bread (CB) (50/50), bagasse and vinasse (BV), bagasse and molasses (BM), bagasse, vinasse, and molasses (BVM), a mixture of all the above treatments (MX), and university canteen leftovers (UCLs). The larval weight and length were measured for two weeks from day 5 to 19. Then, the BSFL were harvested and analyzed for dry matter, crude protein, oil, ash, mineral, and fatty acid composition. Larval weight and length varied depending on the feeding substrate provided. University canteen leftovers resulted in the BSFL having at least 18% greater length (17.00 mm) and 56% greater weight (3.15 g) compared to other treatments. The highest amounts of protein (38.9%) and oil (39.06%) were observed in the UCL treatment, while the BV treatment larvae had the highest quantities of ash (28.9%) and dry matter (28.0%). The fatty acid profile of the BSFL revealed three-times-higher levels of saturated fatty acids than unsaturated fatty acids in the UCL treatment and was at least twice as high in other treatments. Overall, the BSFL had the best growth on the UCL substrate, and the combination of bagasse and vinasse (BV) was the most appropriate substrate for BSFL development among the sugarcane by-products.

Genetic structure of black soldier flies in northern Iran

BACKGROUND

The black soldier fly (BSF), Hermetia illucens, is known for nutrient-recycling through the bioconversion of organic waste into protein-rich insect larvae that can be processed into an animal feed ingredient. However, information on species distribution and its genetic structure in Iran is scarce.

METHODS AND RESULTS

We directed a survey on the Caspian Sea coast, with a reconstructing demographic relationships study using two parts of mitochondrial cytochrome C oxidase 1 (COI) gene (barcode and 3' end regions) and nuclear internal transcribed spacer 2 (ITS2) to identify BSF' genetic diversity in retrospect to the global diversity and the potential origin of the Iranian BSF population. Larvae and adults were recovered from highly decomposed poultry manure, in May 2020. Sequence analysis of both regions of COI gene (about 1500 bp) revealed a single haplotype, identical to that of haplotype C, a worldwide commercial strain originated from Nearctic, Palearctic, or African biogeographic regions. However, the ITS2 locus was confirmed to be invariable across samples from diverse biogeographic regions.

CONCLUSION

The results proved the presence of BSF in north of Iran. However, it is not possible to determine with certainty when and where this species first established in Iran, and they have likely been released to nature due to the existence of companies importing and breeding such flies. Due to heavy international trading, the introduction and settlement of this fly in the southern coasts of the country is highly suggested.

Larval diet impacts black soldier fly (Diptera: Stratiomyidae) thermal tolerance and preference

Thermal tolerance and preference are key parameters impacting agricultural production systems. In this study, the impact of larval diet on black soldier fly thermal tolerance and preference across life-stages and sexes was examined. Larvae were fed either a low-protein high-carbohydrate synthetic diet (i.e., P7C35), a high-protein low-carbohydrate synthetic diet (i.e., P35C7), or the Gainesville diet (i.e., C) as a control and reference. Our results demonstrate that the impacts of larval diet on black soldier fly thermal tolerance and preference could be stage and sex specific. The mean heat knockdown temperatures (HKT) ranged between 46.6 and 47.9 °C. Synthetic diets resulted in greater HKT and the difference decreased form larvae (e.g., ∼1 °C) to adults (e.g., ∼0.2 °C). The mean chill-coma recovery time (CCRT) ranged between 8.3 and 21.6 min. Not much differences were detected between diets, but CCRT became longer from larvae to adults. The mean thermal preference ranged between 13.6 and 29.5 °C. Larvae fed synthetic diets preferred much lower temperatures than the control diet. A bimodal distribution was observed for adults regardless of sex. Differences on body mass, lipid, and protein contents were detected among diets; however, more research should be done before any conclusions can be linked to their thermal traits. These findings highlight the importance of considering the ingredients and nutritional makeup of larval diets when optimizing temperature management protocols for mass production of black soldier flies. Conversely, specific diets can be developed to promote survival under extreme rearing temperatures.

Performance of feeding black soldier fly (Hermetia illucens) larvae on shrimp carcasses: A green technology for aquaculture waste management and circular economy

Over 944 thousand tonnes of shrimp carcasses are produced worldwide during the shrimp production cycle, and black soldier fly larvae (BSFL) are a potential solution for this shrimp carcass accumulation. In this study, we evaluated the performance of BSFL feeding on shrimp carcasses. Six combinations of wheat bran and shrimp carcass powder (with replacement increments of 20 %) and one whole shrimp carcasses treatment were tested. The bioconversion rate (27.15 ± 3.66 %; p = 0.001), crude protein (55.34 ± 1.27 %; p < 0.001), and crude lipid (14.37 ± 1.86 %; p = 0.007) values of BSFL reared on whole shrimp carcasses were significantly higher than those of BSFL reared on wheat bran. Increasing the shrimp carcass amount in the feeding media resulted in significant increases in BSFL docosahexaenoic acid (with the highest value occurring for BSFL reared on whole shrimp carcasses; 1.46 ± 0.09 %; p < 0.001). Conversely, BSFL docosahexaenoic acid was not detected for BSFL reared on wheat bran. The detected heavy metal concentrations in BSFL were below the limits of the published international guidelines for animal feed. In the obtained BSFL, Salmonella was not detected, and the mould count was <10 CFU/g. The total bacterial count (Lg transformation) of obtained BSFL ranged from 7.88 to 8.07 CFU/g, and no significant differences among all treatments (p = 0.424). Overall, this study demonstrates that BSFL-based bioconversion presents a resource recovery technology for converting shrimp carcasses into high-value nutritional biomass.

Development of Phormia regina at seven constant temperatures for minimum postmortem interval estimation

Phormia regina (Meigen, 1826) (Diptera: Calliphoridae) can colonize carcasses quickly, and its immature stages are reliable entomological evidence for the estimation of the minimum postmortem interval (PMImin). There are discrepancies in the developmental data from previous studies on P. regina, and the related PMImin indicators need to be refined. We investigated the accuracy of forensic entomological evidence using development durations, growth accumulated degree hours, and larval body length variations of P. regina at seven constant temperatures ranging from 16 to 34 °C. We also established development models such as the isomorphen diagram, thermal summation model, isomegalen diagram, and body length simulation equation to assist with PMImin estimation. The developmental duration of P. regina from egg to adult at 16, 19, 22, 25, 28, 31, and 34 °C was 840.8 ± 42.8 h, 580.1 ± 10.1 h, 390.4 ± 8.7 h, 316.8 ± 9.4 h, 291.4 ± 21.2 h, 238.4 ± 2.8 h, and 222.5 ± 5.2 h, respectively. The lower threshold temperature TL was 9.97 ± 0.50 °C, while the thermal constant K was 5052.7 ± 229 degree days. The lower developmental thresholds, intrinsic optimum temperature, and upper lethal developmental threshold obtained by the Optim SSI models were 13.15, 21.20, and 36.86 °C, respectively. This study aims to provide developmental models for P. regina aimed at common case-site temperatures in the northern provinces of China, which can be used for accurate PMImin estimation.

Assessing Substrate Utilization and Bioconversion Efficiency of Black Soldier Fly (Hermetia illucens) Larvae: Effect of Diet Composition on Growth and Development Temperature

Black soldier fly larvae (BSFL) can utilize food by-products or residues for growth, benefiting farm animal's diets' production sustainability. The experiment aimed to assess the effect of different substrate compositions on larval growth, chemical composition, and substrate temperature. BSFL were allocated to one of the four diets (control, vegetable, carnivorous, and omnivorous) for the entire experiment (8 days). The temperature was measured twice daily using a thermal-imaging camera, and the accumulated degree hours (ADH) was calculated. The results showed that the larvae fed the vegetable diet exhibited a significantly reduced growth performance, with a biomass reduction of 26.3% compared to the control diet; furthermore, vegetable-fed larvae showed a lower dry matter content (-30% compared to the average of other diets) due to lower fat content (-65% compared to average of other diets). The nutritional composition of larvae fed an omnivorous diet was similar to larvae fed a high-quality substrate diet (control diet-chicken feed), indicating that the omnivorous diet could be an ideal solution for rearing BSFL larvae; however, the current European legislation prohibits the use of animal meal. The study also revealed that substrate temperatures did not have a discernible influence on larval growth, further emphasizing the importance of diet in BSFL rearing strategies.

Laboratory-adapted and wild-type black soldier flies express differential plasticity in bioconversion and nutrition when reared on urban food waste streams

BACKGROUND

The black soldier fly (BSF) offers a potential solution to address shortages of feed and food sources; however, selecting effective rearing substrates remains a major hurdle in BSF farming. In an urban area like Singapore, current practice is based on rearing BSF on homogeneous waste streams (e.g., spent brewery grains or okara) because heterogeneous food wastes (e.g., mixed kitchen/canteen waste or surplus cooked food) present several operational challenges with respect to the standardization of development, nutritional content, and harvesting.

RESULTS

In this study, we compared two genetic strains of BSF larvae (wild-type and laboratory-adapted line) in a bioconversion experiment with diverse types of food waste (homogeneous/heterogeneous; plant/meat) and we quantified the phenotypic plasticity. Our results demonstrate different plasticity in bioconversion performance, larval growth and larval nutrition between the two BSF lines. This difference may be attributed to the selective breeding the laboratory-adapted line has experienced. Notably, larval lipid content displayed little to no genetic variation for plasticity compared with larval protein and carbohydrate content. Despite variation in larval development, heterogeneous food wastes can produce better performance in bioconversion, larval growth, and larval nutrient content than homogeneous food waste. All-meat diets result in high larvae mortality but larval survival could be rescued by mixing meat with plant-based food wastes.

CONCLUSION

Overall, we suggest using mixed meals for BSF larvae feeding. Targeted breeding may be a promising strategy for the BSF industry but it is important to consider the selection effects on plasticity in larval nutrition carefully. © 2023 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Control study of Musca domestica (Diptera, Muscidae) in Misan Province

Background

Houseflies are the most common type of Diptera, specifically Muscidae, worldwide, representing more than 90% of all species. This family has over 170 genera and 4200 species, but a few are of medical significance. This study aimed to estimate and assessing the measures to control and prevent grow-up inside houses and flying of the housefly ( Musca domestica Linnaeus, 1758) in Misan.

Methods

The study occurred over 12 months, from December 2020 to December 2021. Using plastic containers, Musca domestica were collected from all potential breeding sites in the study region (inside and around houses). Sticky oil paper and traps were used to collect the insects. The collected insects were transferred to sealed plastic containers and then to the laboratory of the Department of Microbiology.Out of 200 randomly selected houses, 150 (75%) contained insects. Light traps and sticky oil papers were the most effective control measures, with 26.7% and 25.9% of the Musca domestica collected from these methods, respectively. The ratio of male (233) to female (456) Musca was 1:2, with a significant difference between the frequencies (P<0.05). A large population of houseflies was collected during the hot season (501, 72.7%), whereas fewer Musca were collected during the cold months (188, 27.3%), with a strongly significant difference (P<0.05). The percentage of HI was 54.4%, the CI was 21.9%, and the BI was 79.9%. The overall larval densities (LD) were at a medium level.

Conclusions

Misan has a high density of Musca domestica, with females being more prominent than males. Hot climate, humid sites, and dirty places are responsible for the breeding of houseflies. The overall larval density was medium. Therefore, the risk of transmitting infectious diseases by houseflies is high within the boundaries of Misan province, and effective control parameters should include measures like light traps and sticky oil.

Deciphering the functional diversity of the gut microbiota of the black soldier fly (Hermetia illucens): recent advances and future challenges

Bioconversion using insects is a promising strategy to convert organic waste (catering leftovers, harvest waste, food processing byproducts, etc.) into biomass that can be used for multiple applications, turned into high added-value products, and address environmental, societal and economic concerns. Due to its ability to feed on a tremendous variety of organic wastes, the black soldier fly (Hermetia illucens) has recently emerged as a promising insect for bioconversion of organic wastes on an industrial scale. A growing number of studies have highlighted the pivotal role of the gut microbiota in the performance and health of this insect species. This review aims to provide a critical overview of current knowledge regarding the functional diversity of the gut microbiota of H. illucens, highlighting its importance for bioconversion, food safety and the development of new biotechnological tools. After providing an overview of the different strategies that have been used to outline the microbial communities of H. illucens, we discuss the diversity of these gut microbes and the beneficial services they can provide to their insect host. Emphasis is placed on technical strategies and aspects of host biology that require special attention in the near future of research. We also argue that the singular digestive capabilities and complex gut microbiota of H. illucens make this insect species a valuable model for addressing fundamental questions regarding the interactions that insects have evolved with microorganisms. By proposing new avenues of research, this review aims to stimulate research on the microbiota of a promising insect to address the challenges of bioconversion, but also fundamental questions regarding bacterial symbiosis in insects.

Improvement in bioconversion efficiency and reduction of ammonia emission by introduction of fruit fermentation broth in a black soldier fly larvae and kitchen waste conversion system

The black soldier fly (BSF), Hermetia illucens (Diptera: Stratiomyidae), is an insect commonly used for the bioconversion of various organic wastes. Not only can the BSF convert organic waste into macromolecular organic substances, such as insect proteins, but it can also lessen the pollution associated with these waste products by reducing ammonia emissions, for example. In this study, we measured the effects of adding fruit fermentation broth (Fer) and commercial lactic acid bacteria fermentation broth (Em) to kitchen waste (KW), as deodorizing auxiliary substances, on the growth performance of black soldier fly larvae (BSFL), the intestinal flora structure of BSFL, the ammonia emission from the KW substrate, and the microbial community structure of the KW substrate. We found that the addition of Fer or Em increased the body weight of BSFL after 6 d of culture, increasing the growth rate by 9.96% and 7.96%, respectively. The addition of Fer not only reduced the pH of the KW substrate but also increased the relative abundance of probiotics, such as Lactobacillus, Lysinibacillus, and Vagococcus, which inhibited the growth of ammonifiers such as Bacillus, Oligella, Paenalcaligenes, Paenibacillus, Pseudogracilibacillus, and Pseudomonas, resulting in the reduction of ammonia emission in the KW substrate. Moreover, the addition of Fer or Em significantly increased the relative abundances of Bacteroides, Campylobacter, Dysgonomonas, Enterococcus, and Ignatzschineria in the gut of BSFL and increased the species diversity and richness in the KW substrate. Our findings provide a novel way to improve the conversion rate of organic waste and reduce the environmental pollution caused by BSF.

Feed nutritional composition affects the intestinal microbiota and digestive enzyme activity of black soldier fly larvae

Introduction

Using black soldier fly larvae (BSFLs) to treat food waste is one of the most promising environmental protection technologies.

Methods

We used high-throughput sequencing to study the effects of different nutritional compositions on the intestinal microbiota and digestive enzymes of BSF.

Results

Compared with standard feed (CK), high-protein feed (CAS), high-fat feed (OIL) and high-starch feed (STA) had different effects on the BSF intestinal microbiota. CAS significantly reduced the bacterial and fungal diversity in the BSF intestinal tract. At the genus level, CAS, OIL and STA decreased the Enterococcus abundance compared with CK, CAS increased the Lysinibacillus abundance, and OIL increased the Klebsiella, Acinetobacter and Bacillus abundances. Diutina, Issatchenkia and Candida were the dominant fungal genera in the BSFL gut. The relative abundance of Diutina in the CAS group was the highest, and that of Issatchenkia and Candida in the OIL group increased, while STA decreased the abundance of Diutina and increased that of Issatchenkia. The digestive enzyme activities differed among the four groups. The α-amylase, pepsin and lipase activities in the CK group were the highest, and those in the CAS group were the lowest or the second lowest. Correlation analysis of environmental factors showed a significant correlation between the intestinal microbiota composition and digestive enzyme activity, especially α-amylase activity, which was highly correlated with bacteria and fungi with high relative abundances. Moreover, the mortality rate of the CAS group was the highest, and that of the OIL group was the lowest.

Discussion

In summary, different nutritional compositions significantly affected the community structure of bacteria and fungi in the BSFL intestinal tract, affected digestive enzyme activity, and ultimately affected larval mortality. The high oil diet gave the best results in terms of growth, survival and intestinal microbiota diversity, although the digestive enzymes activities were not the highest.

Black soldier fly (Diptera: Stratiomyidae) larval heat generation and management

Mass production of black soldier fly, Hermetia illucens (L.) (Diptera: Stratiomyidae), larvae results in massive heat generation, which impacts facility management, waste conversion, and larval production. We tested daily substrate temperatures with different population densities (i.e., 0, 500, 1000, 5000, and 10 000 larvae/pan), different population sizes (i.e., 166, 1000, and 10 000 larvae at a fixed feed ratio) and air temperatures (i.e., 20 and 30 °C) on various production parameters. Impacts of shifting larvae from 30 to 20 °C on either day 9 or 11 were also determined. Larval activity increased substrate temperatures significantly (i.e., at least 10 °C above air temperatures). Low air temperature favored growth with the higher population sizes while high temperature favored growth with low population sizes. The greatest average individual larval weights (e.g., 0.126 and 0.124 g) and feed conversion ratios (e.g., 1.92 and 2.08 g/g) were recorded for either 10 000 larvae reared at 20 °C or 100 larvae reared at 30 °C. Shifting temperatures from high (30 °C) to low (20 °C) in between (∼10-d-old larvae) impacted larval production weights (16% increases) and feed conversion ratios (increased 14%). Facilities should consider the impact of larval density, population size, and air temperature during black soldier fly mass production as these factors impact overall larval production.

Temperature-modulated host-pathogen interactions between Hermetia illucens L. (Diptera: Stratiomyidae) and Pseudomonas protegens Pf-5

Temperature is an important abiotic factor influencing the survival and fitness of pathogens as well as their hosts. We investigated the effect of three temperatures (18°C, 27°C and 37°C) on survival and performance of black soldier fly larvae (BSFL), Hermetia illucens L., upon infection by an entomopathogenic Gram-negative bacterium, Pseudomonas protegens Pf-5. The effect of different temperatures on pathogen fitness was investigated both in vivo and in vitro. Pathogen performance under exposure to the insect antimicrobial peptide cecropin was investigated at the three temperatures using radial-diffusion plate assays. Higher rearing temperatures resulted in higher larval survival, increased larval weight, and higher inhibitory activity of cecropin against P. protegens Pf-5. At higher temperature, bacterial growth, both in vivo and in vitro, was reduced, resulting in increased BSFL survival. These observations collectively indicate the important effect of rearing temperature on host-pathogen interactions and the possibility to apply temperature treatment in reducing entomopathogen effects in BSFL.

Effect of Adding De-Oiled Kitchen Water on the Bioconversion of Kitchen Waste Treatment Residue by Black Soldier Fly Larvae

With the continuous development of society, the output of kitchen waste (KW) is fast increasing. De-oiled kitchen water (DKW) and kitchen waste treatment residue (KWTR), two main by-products of the KW treatment industry, are produced accordingly on a large scale. The need to develop an effective technique for the utilization of DKW and KWTR is attracting wide attention. In the present study, black soldier fly larvae (BSFL) were employed as a biological treatment method to treat KWTR with the addition of DKW. The influence of DKW (0-140 mL) on the efficiency of BSFL treatment evaluated by the growth and development of BSFL, the body composition of BSFL, the nutrient content of bioconversion residue (BR), and the bioconversion efficiency of KWTR, was investigated. The results showed that the growth and development of BSFL, the body composition of BSFL, and the conversion rate of KWTR were initially promoted and then inhibited with the addition of DKW. Notably, the amount of DKW added in the T110 group was the most suitable for the growth of BSFL and the accumulation of body composition. Compared with the blank comparison group, the content of crude protein (CP), crude ash (CA), salinity, total phosphorus (TP), and dry matter (DM) of BSFL in the T110 group increased by 3.54%, 6.85%, 0.98%, 0.07% and 2.98%, respectively. However, the addition of DKW could steadily increase the nutrient content of BR, with the highest amount at 140 mL DKW. Following DKW addition, the contents of CP, ether extract (EE), crude fiber (CF), organic matter (OM), total nitrogen (TN), TP, and total potassium (TK) were increased by 4.56%, 3.63%, 10.53%, 5.14%, 0.73%, 0.75%, and 0.52%, respectively, compared with those of the blank comparison group. The study showed that DKW could be used as a nutrient additive in the bioconversion process of KWTR by BSFL, which provided a new method for the resource utilization of DKW.

Performance evaluation of black soldier fly larvae fed on human faeces, food waste and their mixture

In this study, Black Soldier Fly Larvae (BSFL)-based technology has been proposed and tested for treatment and valorization of human faeces, food waste and a mixture of 75% human faeces with 25% food waste. Experiments were conducted between 15 and 45 °C and 55-75% relative humidity. BSFL's performance for the degradation of the mixed waste was significantly better than their performances when used for the degradation of either human faeces or food waste fed alone, primarily due to the availability of more conducive pH, and better microbial and nutrient balance. The abiotic factors, temperature and relative humidity impacted the decomposition rate and weight gain pattern of BSFL when they were fed on the waste streams. The results showed that the optimum conditions to conduct the proposed BSFL-based treatment was 31-35 °C and 55-75% RH. The protein content in the BSFL was not impacted significantly by the quality of the waste stream, whereas the fat content varied substantially. The abiotic factors also impacted the protein and fat content of BSFL. The investigation led to the estimation of the decomposition rates over a wide range of temperature and relative humidity conditions, which could be useful for the design of large-scale BSFL-based treatment plants.

Effects of Tissue Type and Temperature on Selected Life-History Traits of the Flesh Fly, Sarcophaga crassipalpis (Macquart, 1839) (Diptera: Sarcophagidae)

The flesh fly, Sarcophaga crassipalpis Macquart 1839 (Diptera: Sarcophagidae), colonizes estimation of the minimum post-mortem interval (min-PMI). This study examined the effects of different types of tissues and temperature on the development of S. crassipalpis. To the best of our knowledge, the present study is the first to investigate the effects of life-history information of S. crassipalpis. Larvae were reared on three tissue types, chicken heart, bovine minced meat, and bovine tongue, at five temperatures, 15, 20, 25, 30, and 32°C. Pupal and larval development time, adult weight, and pupal and larval survival differed significantly for tissue type and temperature. Temperature had a significant effect on pupal weight but tissue type did not significantly affect pupal weight. The duration of the larval and pupal stages (except of chicken heart, 30°C) decreased with increasing temperature, except for 32°C, in all tissue types. Larval survival was lowest at 32°C in bovine minced meat, bovine tongue, and chicken heart, and at 32°C, all pupae failed to reach the adult stage in minced meat. The results of this study highlight the necessity of considering larval diet and temperature in forensic investigations.

Black soldier fly (Hermetia illucens L.) as a high-potential agent for bioconversion of municipal primary sewage sludge

The treatment of municipal wastewater produces clean water and sewage sludge (MSS), the management of which has become a serious problem in Europe. The typical destination of MSS is to spread it on land, but the presence of heavy metals and pollutants raises environmental and health concerns. Bioconversion mediated by larvae of black soldier fly (BSFL) Hermetia illucens (Diptera, Stratiomyidae: Hermetiinae) may be a strategy for managing MSS. The process adds value by generating larvae which contain proteins and lipids that are suitable for feed and/or for industrial or energy applications, and a residue as soil conditioner. MSS from the treatment plant of Ladispoli (Rome province) was mixed with an artificial fly diet at 50% and 75% (fresh weight basis) to feed BSFL. Larval performance, substrate reduction, and the concentrations of 12 metals in the initial and residual substrates and in larval bodies at the end of the experiments were assessed. Larval survival (> 96%) was not affected. Larval weight, larval development, larval protein and lipid content, and waste reduction increased in proportion the increase of the co-substrate (fly diet). The concentration of most of the 12 elements in the residue was reduced and, in the cases of Cu and Zn, the quantities dropped under the Italian national maximum permissible content for fertilizers. The content of metals in mature larvae did not exceed the maximum allowed concentration in raw material for feed for the European Directive. This study contributes to highlight the potential of BSF for MSS recovery and its valorization. The proportion of fly diet in the mixture influenced the process, and the one with the highest co-substrate percentage performed best. Future research using other wastes or by-products as co-substrate of MSS should be explored to determine their suitability.

Morphometric Characteristic of Black Soldier Fly (Hermetia illucens) · Wuhan Strain and Its Egg Production Improved by Selectively Inbreeding

The use of black soldier fly (BSF) larvae to recycle various organic materials while producing biomass for use as feed is well established. Variety selection is important from the perspective of application. In the current study, morphometric and life-history traits of a Wuhan-domesticated BSF colony (Wuhan strain) were compared to those of a 'selectively inbred' population (inbred strain, inbred for 10 generations). In terms of morphological characteristics, the results showed that both strains had dichoptic compound eyes, club-shaped antennae, blue halters, and blue-green metallic luster wings with a hexagon discal cell. In both strains, the body and wing length of female adults were slightly larger than those of male adults. The first four larval stages of the BSF occurred rapidly (1-12 days) with transitions across stages resulting in doubling of size for both populations. Selective inbreeding did not alter the life-history traits of the larval exuviate stage in terms of age, size, weight, and feed reduction rate. Overall egg production for the inbred strain was significantly higher (1.5 times greater) than the Wuhan strain. This is explained by increased adult emergence and individual oviposition performance. It was speculated that inbreeding improved the reproductive success of inbred adult female offspring and selection process steadied it. The findings indicate that selective inbreeding could enhance overall oviposition performance and provide a strategy to selectively breed BSF with high egg production for future applications.

A Fly in the Ointment: How to Predict Environmentally Driven Phenology of an Organism That Partially Regulates Its Microclimate

Phenological models representing physiological and behavioral processes of organisms are used to study, predict, and optimize management of ecological subsystems. One application of phenological models is the prediction of temporal intervals associated with the measurable physiological development of arthropods, for the purpose of estimating future time points of interest such as the emergence of adults, or estimating past time points such as the arrival of ovipositing females to new resources. The second of these applications is of particular use in the conduct of forensic investigations, where the time of a suspicious death must be estimated on the basis of evidence, including arthropods with measurable size/age, found at the death scene. Because of the longstanding practice of using necrophagous insects to estimate time of death, standardized data and methods exist. We noticed a pattern in forensic entomological validation studies: bias in the values of a model parameter is associated with improved model fit to data, for a reason that is inconsistent with how the models used in this practice are interpreted. We hypothesized that biased estimates for a threshold parameter, representing the lowest temperature at which insect development is expected to occur, result in models’ accounting for behavioral and physiological thermoregulation but in a way that results in low predictive reliability and narrowed applicability of models involving these biased parameter estimates. We explored a more realistic way to incorporate thermoregulation into insect phenology models with forensic entomology as use context, and found that doing so results in improved and more robust predictive models of insect phenology.

Effects of three major nutrient contents, compost thickness and treatment time on larval weight, process performance and residue component in black soldier fly larvae (Hermetia illucens) composting

The cellulose content in vegetable waste (VW) is high and cannot be directly digested by black soldier fly larvae (BSFL). In this study, in order to treat VW using BSFL composting, kitchen waste (KW) is used as the only nutritional supplement for VW to analyze the effects of the different contents of crude protein (CP), crude fat (EE), carbohydrate (3C), compost thickness (CT), and treatment time on the larval weight (LW), survival rate (SR), dry matter reduction rate (DMR), bioconversion rate (BCR), physical and chemical properties of BSFL sand and changes in the microbial community. Our results showed that when the average 3C content increased by 40%, the average LW increased by 47.6%, and the SR, DMR, BCR, and organic matter (OM) content increased by 16.82%, 8.5%, 4.77%, and 3.86%, respectively. In contrast, when the average compost thickness increased by 5 cm, the average weight of BSFL decreased by 22.64%, while the SR of larvae, DMR, BCR, OM, and total nutrients (TN + P₂O₅ + K₂O) decreased by 5%, 5.2%, 4.42%, 9.6%, and 0.78%, respectively. Germination test showed that BSFL sand alone could not be used as soilless culture substrate. After BSFL treatment, we found that the dominant phyla in BSFL sand were Firmicutes (95.77%), Proteobacteria (2.54%), Actinobacteria (0.74%), and Chloroflexi (0.6%). Our results indicate that BSFL composting is an effective method of treating VW, and 3C content and CT have a significant effect on BSFL composting.

Growth of the Black Soldier Fly Hermetia illucens (Diptera: Stratiomyidae) on Organic-Waste Residues and Its Application as Supplementary Diet for Nile Tilapia Oreochromis niloticus (Perciformes: Cichlidae)

The black soldier fly, Hermetia illucens (BSF, Diptera: Stratiomyidae) is an insect with high protein value and a potential feed agent for animals aimed for human consumption. The growth parameters of BSF larvae reared on four substrates—restaurant-waste, fruit-waste, fish-waste, and commercial tilapia food—for 41 days before processing for inclusion into Oreochromis niloticus (Perciformes: Cichlidae, Nile tilapia) commercial fry diets at 30% (70:30) were determined. On fly larvae, the food substrate based on restaurant waste yielded the greatest larval weight and length. BSF larvae fed a fish-waste diet showed the shortest developmental time. The fruit-waste diet induced the lowest weight and length in the fly larvae/pre-pupae (immature stage). The pre-pupal protein values were similar to commercial food. On fry-fish, the diets with pre-pupae grown on fish waste showed the greatest yields regarding weight (biomass), length, and nutritional content. These results suggest the BSF has the potential to be used in fish feed and provides an alternative for commercial cultivation.

The Effect of Rearing Scale and Density on the Growth and Nutrient Composition of Hermetia illucens (L.) (Diptera: Stratiomyidae) Larvae

With the worldwide industrialization of black soldier fly (BSF) production, it is necessary to better understand how the rearing scale and larvae density influence the performance of larvae and the quality of the final product. In this study, a factorial experiment was conducted to test the effect of rearing scale and density on the growth and composition of the BSF larvae. The larvae were grown in four different scales (box sizes), keeping the area and feed provided to each larva constant and in two different densities. The results reveal significant differences in the larval growth depending on the scale and density, which could be attributed to the higher temperatures achieved in the bigger scales with a temperature difference of more than 5 °C between the smallest and the biggest scale. Both the scale and the density influenced the composition of the larvae. The crude protein levels were higher on the smallest scale, and the lower density (ranging from 32.5% to 36.5%), and crude fat concentrations were the opposite (ranging from 31.7% to 20.1%). The density also influenced the concentrations of S, Mg, K, P, Fe, Zn, Cu, Al, B, and Co, in addition to the analyzed free amino acids PPS, ALA, CIT, and ANS. Furthermore, the rearing scale influenced the concentration of S, Zn, Cu, and Mo. The results provide further insight into the optimization of BSF production processes and the transfer of lab-scale results into big-scale production.

Black soldier fly larvae for treatment and segregation of commingled municipal solid waste at different environmental conditions

The commingled nature of the municipal solid waste in many developing nations is one of the primary reasons behind the failure to its successful management. Although there are technologies to effectively treat and process well-segregated and classified waste, they are ineffective in managing the commingled waste. Commingled waste has neither calorific value enough to support waste-to-energy operations nor is it suitable for producing quality compost to generate market value. In this article, a novel Black Soldier Fly Larva (BSFL) -based technology has been proposed and tested to auto-segregate and treat the biodegradable fraction of the Commingled Municipal Solid Waste (CMSW). Several BSFL feeding experiments on five different CMSW compositions were conducted at various temperatures and relative humidity conditions. BSFL could selectively consume the biodegradable fraction of the CMSW to convert it into its body mass and separate itself from the rest of the waste, which mainly consisted of inert and recyclable waste fractions that can be further treated using appropriate waste treatment technology. The mature larvae or the pre-pupae grown at the expense of the biodegradable waste fraction can find several commercial uses. The larvae's consumption rate and weight gain were dependent on the environmental conditions; 30 °C and relative humidity of 65-75% provided the highest consumption rate and most significant weight gain. The batch experiments in the laboratory proved that BSFL could be promising for the treatment of CMSW. The experimental data presented may help design a process for further scaling up an effective treatment method for CMSW, which might benefit many developing nations in managing their waste effectively and economically.

Predicting black soldier fly larvae biomass and methionine accumulation using a kinetic model for batch cultivation and improving system performance using semi-batch cultivation

Global demand for poultry and associated feed are projected to double over the next 30 years. Insect meal is a sustainable alternative to traditional feeds when produced on low-value high-volume agricultural byproducts. Black soldier fly (BSF) larvae (Hermetia illucens L.) are high in protein and contain methionine, an essential amino acid that is critical to poultry health. BSF larvae can be grown on many organic residues, however, larvae growth and quality vary based on feedstock and cultivation processes. Experiments were completed to monitor temporal changes in BSF larvae growth and composition using almond hulls as a growth substrate under batch and semi-batch processes and with varying substrate carbon to nitrogen ratio (C/N). A logistic kinetic growth model was developed to predict larval biomass and methionine accumulations during batch production. Estimated ranges of model parameters for larvae maximum specific growth rate and carrying capacity were 0.017–0.021 h⁻¹ and 9.7–10.7 g larvae kg⁻¹ hulls dry weight, respectively. Methionine content in larvae increased from 11.1 to 17.1 g kg⁻¹ dry weight over a 30-day batch incubation period. Larvae-specific growth and yield increased by 168% and 268%, respectively, when cultivated in a semi-batch compared to a batch process. Increasing C/N ratio from 26 to 40 increased density of methionine content in larvae per unit feedstock by 25%. The findings demonstrate a logistic model can predict larvae biomass accumulation, harvest time can achieve specific methionine contents, and a semi-batch process is more favorable for larvae biomass accumulation compared to a batch process.

Nature-Based Units as Building Blocks for Resource Recovery Systems in Cities

Cities are producers of high quantities of secondary liquid and solid streams that are still poorly utilized within urban systems. In order to tackle this issue, there has been an ever-growing push for more efficient resource management and waste prevention in urban areas, following the concept of a circular economy. This review paper provides a characterization of urban solid and liquid resource flows (including water, nutrients, metals, potential energy, and organics), which pass through selected nature-based solutions (NBS) and supporting units (SU), expanding on that characterization through the study of existing cases. In particular, this paper presents the currently implemented NBS units for resource recovery, the applicable solid and liquid urban waste streams and the SU dedicated to increasing the quality and minimizing hazards of specific streams at the source level (e.g., concentrated fertilizers, disinfected recovered products). The recovery efficiency of systems, where NBS and SU are combined, operated at a micro- or meso-scale and applied at technology readiness levels higher than 5, is reviewed. The importance of collection and transport infrastructure, treatment and recovery technology, and (urban) agricultural or urban green reuse on the quantity and quality of input and output materials are discussed, also regarding the current main circularity and application challenges.

Research Progress on Developmental Biology of Sarcosaprophagous Insects

Forensic entomology provides a feasible way to estimate postmortem interval (PMI), of which the growth and development of sarcosaprophagous insects is the most widely used indicator in forensic practice. Over the years, forensic entomologists have carried out a large number of studies on the development biology of sarcosaprophagous insects. This paper illustrates the main factors that affect the development of sarcosaprophagous insects, including temperature, humidity, light, food types and poisons. The development indicators of sarcosaprophagous insects were reviewed from the perspectives of morphology, differential gene expression and biochemical characteristics. It is emphasized that future research of development biology on sarcosaprophagous insects should fully absorb and integrate the methods of artificial intelligence and omics, and the research object also needs further expansion in order to establish a more objective and more accurate PMI estimation method.

Ovitrap Preference in the Black Soldier Fly, Hermetia illucens (L.) (Diptera: Stratiomyidae)

&lt;b&gt;Background and Objective:&lt;/b&gt; The adult female of the Black Soldier Fly (BSF) usually performs oviposition near decaying organic matter in cracks found in dry areas. In mass-rearing facilities or on a laboratory scale, females usually lay eggs on the provided ovitrap which is made of various types of materials. This study was aimed to observe the female preferential behaviour for ovitrap types during the oviposition period. &lt;b&gt;Materials and Methods:&lt;/b&gt; The study was conducted in a semi-outdoor screen house with direct sunlight. The ovitrap materials used were: Dry leaves, wood, cardboard and plastic (infraboard). The parameters calculated in this study were ovitrap preference, oviposition duration, the number and weight of the eggs, fertility of eggs, development time and mortality of offspring. &lt;b&gt;Results:&lt;/b&gt; The BSF females preferred the wood ovitrap to other ovitrap types. This was indicated by the high number of females visits, the number of egg-laying females and the total number of eggs on the wood ovitrap. Eggs found in the plastic ovitrap had the highest mortality compared to eggs found in the other ovitraps. &lt;b&gt;Conclusion:&lt;/b&gt; The difference of ovitrap material affected female visitation preferences, the oviposition frequency and the duration of egg-laying of female BSF but did not affect offspring development time in any of the stages (egg-adults).

Evaluation of Development Datasets for Hermetia illucens (L.) (Diptera: Stratiomyidae) for Estimating the Time of Placement of Human and Swine Remains in Texas, USA

A basic tenet of forensic entomology is development data of an insect can be used to predict the time of colonization (TOC) by insect specimens collected from remains, and this prediction is related to the time of death and/or time of placement (TOP). However, few datasets have been evaluated to determine their accuracy or precision. The black soldier fly, Hermetia illucens (L.) (Diptera: Stratiomyidae) is recognized as an insect of forensic importance. This study examined the accuracy and precision of several development datasets for the black soldier fly by estimating the TOP of five sets of human and three sets of swine remains in San Marcos and College Station, TX, respectively. Data generated from this study indicate only one of these datasets consistently (time-to-prepupae 52%; time-to-eclosion 75%) produced TOP estimations that occurred within a day of the actual TOP of the remains. It is unknown if the precolonization interval (PreCI) of this species is long, but it has been observed that the species can colonize within 6 d after death. This assumption remains untested by validation studies. Accounting for this PreCI improved accuracy for the time-to-prepupae group, but reduced accuracy in the time-to-eclosion group. The findings presented here highlight a need for detailed, forensic-based development data for the black soldier fly that can reliably and accurately be used in casework. Finally, this study outlines the need for a basic understanding of the timing of resource utilization (i.e., duration of the PreCI) for forensically relevant taxa so that reasonable corrections may be made to TOC as related to minimum postmortem interval (mPMI) estimates.

Effects of Different Nitrogen Sources and Ratios to Carbon on Larval Development and Bioconversion Efficiency in Food Waste Treatment by Black Soldier Fly Larvae (Hermetia illucens)

Simple Summary

Black soldier fly larvae (BSFL) have received global research interest and industrial application due to their high performance on the organic waste treatment. However, the substrate C/N property, which may affect larvae development and the waste bioconversion process greatly, is significantly less studied. The current study focused on the food waste treatment by BSFL, compared the nitrogen supplying effects of 9 nitrogen species (i.e., NH₄Cl, NaNO₃, urea, uric acid, Gly, L-Glu, L-Glu:L-Asp (1:1, w/w), soybean flour, and fish meal), and further examined the C/N effects on the larval development and bioconversion process. We found that NH₄Cl and NaNO₃ led to poor larval growth and survival, while 7 organic nitrogen species exerted no harm to the larvae. Urea was further chosen to adjust the C/Ns. Results showed that lowering the C/N from the initial 21:1 to 18:1–14:1 improved the waste reduction and larvae production performance, and C/N of 18:1–16:1 was further beneficial for the larval protein and lipid bioconversion, whereas C/N of 12:1–10:1 resulted in a significant performance decline. Therefore, the C/N range of 18:1–16:1 is likely the optimal condition for food waste treatment by BSFL and adjusting food waste C/N with urea could be a practical method for the performance improvement.

Abstract

Biowaste treatment by black soldier fly larvae (BSFL, Hermetia illucens) has received global research interest and growing industrial application. Larvae farming conditions, such as temperature, pH, and moisture, have been critically examined. However, the substrate carbon to nitrogen ratio (C/N), one of the key parameters that may affect larval survival and bioconversion efficiency, is significantly less studied. The current study aimed to compare the nitrogen supplying effects of 9 nitrogen species (i.e., NH₄Cl, NaNO₃, urea, uric acid, Gly, L-Glu, L-Glu:L-Asp (1:1, w/w), soybean flour, and fish meal) during food waste larval treatment, and further examine the C/N effects on the larval development and bioconversion process, using the C/N adjustment with urea from the initial 21:1 to 18:1, 16:1, 14:1, 12:1, and 10:1, respectively. The food wastes were supplied with the same amount of nitrogen element (1 g N/100 g dry wt) in the nitrogen source trial and different amount of urea in the C/N adjustment trial following larvae treatment. The results showed that NH₄Cl and NaNO₃ caused significant harmful impacts on the larval survival and bioconversion process, while the 7 organic nitrogen species resulted in no significant negative effect. Further adjustment of C/N with urea showed that the C/N range between 18:1 and 14:1 was optimal for a high waste reduction performance (73.5–84.8%, p < 0.001) and a high larvae yield (25.3–26.6%, p = 0.015), while the C/N range of 18:1 to 16:1 was further optimal for an efficient larval protein yield (10.1–11.1%, p = 0.003) and lipid yield (7.6–8.1%, p = 0.002). The adjustment of C/N influenced the activity of antioxidant enzymes, such as superoxide dismutase (SOD, p = 0.015), whereas exerted no obvious impact on the larval amino acid composition. Altogether, organic nitrogen is more suitable than NH₄Cl and NaNO₃ as the nitrogen amendment during larval food waste treatment, addition of small amounts of urea, targeting C/N of 18:1–14:1, would improve the waste reduction performance, and application of C/N at 18:1–16:1 would facilitate the larval protein and lipid bioconversion process.

Effects of Larval Population Density and Food Type on the Life Cycle of Musca domestica (Diptera: Muscidae)

Larval density is an important factor modulating larval resource-acquisition, influencing development of insects. This study aimed to evaluate the effect of larval density and substrate content on some life-history parameters of Musca domestica Linnaeus, 1758 (Diptera: Muscidae). This research was carried out from March 2019 through September 2019 at Animal Physiology Laboratory of Ondokuz Mayıs University, Samsun, Turkey. Groups of 25, 100, 200, and 400 newly hatched M. domestica larvae were transferred to a polyethylene cup filled with different substrates (i.e., wheat bran, poultry meal, soybean meal) and kept at 25°C, 62% RH with a photoperiod of 12:12 (L:D) h. A two-way analysis of variance (Two way ANOVA) was used to analyze the data on the percentage of pupal and larval survival development time, pupal, and adult weight to evaluate the effect of density and rearing substrate. In this study, increasing larval density and nutrient content of food led to changes in the larval and pupal development time of M. domestica. The results also indicated that the weight of pupae and adult survival was negatively affected by increasing larval density. The wheat bran diet was superior to the other diets for all parameters tested. Our study indicated that life history parameters of Musca domestica are affected by the rearing conditions.

Proteomics and ultrastructural analysis of Hermetia illucens (Diptera: Stratiomyidae) larval peritrophic matrix

BACKGROUND

The black soldier fly (Hermetia illucens) has significant economic potential. The larvae can be used in financially viable waste management systems, as they are voracious feeders able to efficiently convert low-quality waste into valuable biomass. However, most studies on H. illucens in recent decades have focused on optimizing their breeding and bioconversion conditions, while information on their biology is limited.

METHODS

About 200 fifth instar well-fed larvae were sacrificed in this work. The liquid chromatography-tandem mass spectrometry and scanning electron microscopy were employed in this study to perform a proteomic and ultrastructural analysis of the peritrophic matrix (PM) of H. illucens larvae.

RESULTS

A total of 565 proteins were identified in the PM samples of H. illucen, of which 177 proteins were predicted to contain signal peptides, bioinformatics analysis and manual curation determined 88 proteins may be associated with the PM, with functions in digestion, immunity, PM modulation, and others. The ultrastructure of the H. illucens larval PM observed by scanning electron microscopy shows a unique diamond-shaped chitin grid texture.

CONCLUSIONS

It is the first and most comprehensive proteomics research about the PM of H. illucens larvae to date. All the proteins identified in this work has been discussed in details, except several unnamed or uncharacterized proteins, which should not be ignored and need further study. A comparison of the ultrastructure between H. illucens larval PM and those of other insects as observed by SEM indicates that the PM displays diverse textures on an ultra-micro scale and we suscept a unique diamond-shaped chitin grid texture may help H. illucens larval to hold more food. This work deepens our understanding of the molecular architecture and ultrastructure of the H. illucens larval PM.

Post-Mortem Interval Estimation Based on Insect Evidence: Current Challenges

During death investigations insects are used mostly to estimate the post-mortem interval (PMI). These estimates are only as good as they are close to the true PMI. Therefore, the major challenge for forensic entomology is to reduce the estimation inaccuracy. Here, I review literature in this field to identify research areas that may contribute to the increase in the accuracy of PMI estimation. I conclude that research on the development and succession of carrion insects, thermogenesis in aggregations of their larvae and error rates of the PMI estimation protocols should be prioritized. Challenges of educational and promotional nature are discussed as well, particularly in relation to the collection of insect evidence.

Thermal requirements of immature stages of Chrysomya albiceps (Diptera: Calliphoridae) as a common forensically important fly

Entomological material may be used to estimate the time since death occurred (postmortem interval, PMI) in forensically obscure cases. The method that is commonly used to calculate minimum post-mortem interval (mPMI, i.e., the least amount of time since one can be confident death occurred) is based on the relationship between insect development and ambient temerature. Isomegalen and isomorphen diagrams are among methods allowing to calculate the age of necorphagous insects, yet thermal summation models provide the most precise and acurate estimations. The digrams are prepared based on the length or the developmental stages of the larvae as a function of time and mean ambient temperature. A knowledge of thermal requirements, in particular lower temperature threshold (D_z) at which development of a species terminates, is of essential importance to calculate ADD (Accumulated Degree Days). In this study different temperature regimes were used to construct the isomorphen diagram, examinate changes in larval body length at different ambient temperatures and to estimate the thermal requirements for developemnt of Chrysomya albiceps, the most common dipteran species reported on human and animal cadavers in Iran. Six development events including hatching, 1st ecdysis, 2nd ecdysis, wandering, pupariation and eclosion were studied under eleven constant temperature regims (17-37 ⁰C). The development rate of Ch. albiceps increased as temperature increased. The larval length peaked at the end of third stage and then decreased at wandering stage. The maximum larval length occurred at 72 h post oviposition at either 31, 33, or 35 °C. At 17 °C, larvae did not hatch from eggs and at 37 °C wandering larvae did not proceed to pupariation, and thus larval development were analysed at the nine left over temperatures. The development stages required at least (D_z ± SE) 13.04 ± 0.37, 14.29 ± 0.45, 15.69 ± 0.56, 15.18 ± 0.56, 14.94 ± 0.48, and 11.23 ± 0.41 °C to reach one of the successive developmentl events, respectively. The estimated thermal summation constant (k) for those the six events were 10.43 ± 0.27, 19.31 ± 0.32, 27.87 ± 1.3, 55.94 ± 1.82, 66.69 ± 3.5, and 143.52 ± 5.61 ADD accordingly.

Dietary Effects on the Development of Calliphora dubia and Chrysomya rufifacies (Diptera: Calliphoridae): Implications for Postmortem Interval

Forensic entomology relies on insect development data generated within a laboratory setting in the estimation of minimum postmortem interval (mPMI). The methodologies used to produce these data vary considerably within the field and there is no accepted standard approach to laboratory rearing of forensically relevant species. A wide range of rearing media are used across published studies, including different species of animal and types of tissue (e.g., muscle and liver). Differing methodologies, particularly rearing diet, can introduce considerable variation into the baseline data upon which forensic estimates of the mPMI are calculated. Consequently, research establishing a widely available, standard and/or optimal, rearing medium for blow fly development for forensic application is desirable. This study examined dietary effects on the development of two forensically relevant blow fly species: Calliphora dubia Macquart, 1855, and Chrysomya rufifacies Macquart 1842 (Diptera: Calliphoridae). Larvae of both species were reared on pork liver, pork mince, pork loin, beef liver, beef mince, and guinea pig carcass under two constant temperature regimes (24 ± 1°C and 30 ± 1°C; 70 ± 10% humidity; 12-h/12-h photoperiod) to assess the influence of temperature on developmental response to diet. Fundamental developmental data pertaining to both species are reported. Developmental response to diet was species-specific and influenced by temperature with indication that the optimal temperature for C. dubia development is below 30°C. Pork mince was the most appropriate dietary standard of the rearing media investigated for the formulation of forensic development data for both species investigated.

Effects of Bacterial Supplementation on Black Soldier Fly Growth and Development at Benchtop and Industrial Scale

Historically, research examining the use of microbes as a means to optimize black soldier fly (BSF) growth has explored few taxa. Furthermore, previous research has been done at the benchtop scale, and extrapolating these numbers to industrial scale is questionable. The objectives of this study were to explore the impact of microbes as supplements in larval diets on growth and production of the BSF. Three experiments were conducted to measure the impact of the following on BSF life-history traits on (1) Arthrobacter AK19 supplementation at benchtop scale, (2) Bifidobacterium breve supplementation at benchtop scale, and (3) Arthrobacter AK19 and Rhodococcus rhodochrous 21198 as separate supplements at an industrial scale. Maximum weight, time to maximum weight, growth rate, conversion level of diet to insect biomass, and associated microbial community structure and function were assessed for treatments in comparison to a control. Supplementation with Arthrobacter AK19 at benchtop scale enhanced growth rate by double at select time points and waste conversion by approximately 25–30% with no impact on the microbial community. Predicted gene expression in microbes from Arthrobacter AK19 treatment was enriched for functions involved in protein digestion and absorption. Bifidobacterium breve, on the other hand, had the inverse effect with larvae being 50% less in final weight, experiencing 20% less conversion, and experienced suppression of microbial community diversity. For those tested at the industrial scale, Arthrobacter AK19 and R. rhodochrous 21198 did not impact larval growth differently as both resulted in approximately 22% or more greater growth than those in the control. Waste conversion with the bacteria was similar to that recorded for the control. Diets treated with the supplemental bacteria showed increased percent difference in predicted genes compared to control samples for functions involved in nutritional assimilation (e.g., protein digestion and absorption, energy metabolism, lipid metabolism). Through these studies, it was demonstrated that benchtop and industrial scale results can differ. Furthermore, select microbes can be used at an industrial scale for optimizing BSF larval production and waste conversion, while others cannot. Thus, targeted microbes for such practices should be evaluated prior to implementation.

A comprehensive dynamic growth and development model of Hermetia illucens larvae

Larvae of Hermetia illucens, also commonly known as black soldier fly (BSF) have gained significant importance in the feed industry, primarily used as feed for aquaculture and other livestock farming. Mathematical models such as the Von Bertalanffy growth model and dynamic energy budget models are available for modelling the growth of various organisms but have their demerits for their application to the growth and development of BSF. Also, such dynamic models were not yet applied to the growth of the BSF larvae despite models proven to be useful for automation of industrial production process (e.g. feeding, heating/cooling, ventilation, harvesting, etc.). This work primarily focuses on developing a model based on the principles of the afore mentioned models from literature that can provide accurate mathematical description of the dry mass changes throughout the life cycle and the transition of development phases of the larvae. To further improve the accuracy of these models, various factors affecting the growth and development such as temperature, feed quality, feeding rate, moisture content in feed, and airflow rate are developed and integrated into the dynamic growth model. An extensive set of data was aggregated from various literature and used for the model development, parameter estimation and validation. Models describing the environmental factors were individually validated based on the data sets collected. In addition, the dynamic growth model was also validated for dry mass evolution and development stage transition of larvae reared on different substrate feeding rates. The developed models with the estimated parameters performed well, highlighting their potential application in decision-support systems and automation for large scale production.

Almond by-product composition impacts the rearing of black soldier fly larvae and quality of the spent substrate as a soil amendment

BACKGROUND

Insect biomass is a sustainable alternative to traditional animal feeds, particularly when insects are produced on low-value high-volume agricultural by-products. Seven samples of almond by-product (hulls and shells) were obtained from processors in California and investigated for larvae production. Experiments were completed with and without larvae and spent substrate samples were assessed for their potential as soil amendments based on standard compost quality indicators.

RESULTS

On average, specific larvae growth and average larval harvest weight were 158% and 109% higher, respectively, when larvae were reared on Monterey and pollinator hulls compared to nonpareil hulls and mixed shells. Larvae methionine and cystine contents were highest when larvae were reared on Monterey hulls and mixed shells, respectively. Available phytonutrients in spent substrate were affected by feedstock sample and larvae rearing. Spent nonpareil substrate without larvae had the highest NH₄ -N levels and spent pollinator substrate incubated without larvae had the highest PO₄ -P levels. Spent mixed shell substrate had the lowest availability of phytonutrients.

CONCLUSION

The findings demonstrate that by-product composition has a significant impact on larvae growth and the properties of the spent substrate, and that spent substrate from larvae rearing requires further stabilization before application as a soil amendment. © 2020 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Influence of Substrate Age and Interspecific Colonization on Oviposition Behavior of a Generalist Feeder, Black Soldier Fly (Diptera: Stratiomyidae), on Carrion

Variation in resource utilization plays a significant role in determining the success or failure of a species. Generalist species across numerous taxa have exhibited success in feeding strategies for a variety of reasons. This study investigated the colonization and oviposition habits of a generalist carrion-feeder, Hermetia illucens L. (Diptera: Stratiomyidae), to varying conditions of carrion decay and colonization. Oviposition treatments consisted of combinations of variably aged decaying rats, both uncolonized and colonized with a heterospecific carrion-feeder. The black soldier fly exhibited a greater preference for oviposition on aged carrion, regardless of carcass colonization status. However, when presented with the option to colonize a plant-based diet, there was a significantly greater (40.4%) oviposition response to this diet. Results of this study highlight the ability of the black soldier fly to colonize fresh or aged carrion with or without a primary colonizer present, further supporting the recognition of this species as a generalist. These data demonstrate potential inaccuracies in the utility of H. illucens as time of colonization indicator species for legal investigations, and, in some regard, can be considered an exploitative niche-specialist (i.e., relying on plant-carrion interface for immature development) when found in association with carrion.

Effect of Rearing Temperature on Growth and Microbiota Composition of Hermetia illucens

The potential utilization of black soldier fly (Hermetia illucens) as food or feed is interesting due to the nutritive value and the sustainability of the rearing process. In the present study, larvae and prepupae of H. illucens were reared at 20, 27, and 33 °C, to determine whether temperature affects the whole insect microbiota, described using microbiological risk assessment techniques and 16S rRNA gene survey. The larvae efficiently grew across the tested temperatures. Higher temperatures promoted faster larval development and greater final biomass but also higher mortality. Viable Enterobacteriaceae, Bacillus cereus, Campylobacter, Clostridium perfringens, coagulase-positive staphylococci, Listeriaceae, and Salmonella were detected in prepupae. Campylobacter and Listeriaceae counts got higher with the increasing temperature. Based on 16S rRNA gene analysis, the microbiota of larvae was dominated by Providencia (>60%) and other Proteobateria (mainly Klebsiella) and evolved to a more complex composition in prepupae, with a bloom of Actinobacteria, Bacteroidetes, and Bacilli, while Providencia was still present as the main component. Prepupae largely shared the microbiota with the frass where it was reared, except for few lowly represented taxa. The rearing temperature was negatively associated with the amount of Providencia, and positively associated with a variety of other genera, such as Alcaligenes, Pseudogracilibacillus, Bacillus, Proteus, Enterococcus, Pediococcus, Bordetella, Pseudomonas, and Kerstersia. With respect to the microbiological risk assessment, attention should be paid to abundant genera, such as Bacillus, Myroides, Proteus, Providencia, and Morganella, which encompass species described as opportunistic pathogens, bearing drug resistances or causing severe morbidity.

Development and validation of forensically useful growth models for Central European population of Creophilus maxillosus L. (Coleoptera: Staphylinidae)

The hairy rove beetle, Creophilus maxillosus (Linnaeus) (Staphylinidae), is recognized for its use in forensic entomology. However, insufficient developmental data exist for the Central European population of this species. Accordingly, we studied the development of C. maxillosus at ten constant temperatures (10-32.5 °C). Based on these results, linear and nonlinear developmental models were created and validated. We also studied the effect of different homogenous diets (third-instar larvae or puparia of Calliphora sp. Robineau-Desvoidy or Lucilia sp. Robineau-Desvoidy (Diptera: Calliphoridae) or mix of first- and second-instar larvae of Necrodes littoralis (Linnaeus) (Coleoptera: Silphidae)) on the development and mortality of C. maxillosus. Average total development times ranged between 122.21 days at 15 °C and 22.18 days at 30 °C. Beetles reached the adult stage in seven out of ten temperatures (15-30 °C). No beetles reached the adult stage when fed with larvae of N. littoralis; their development times at first and second larval stage were also significantly longer than in other food conditions. When C. maxillosus larvae were fed with blowfly larvae, the highest mortality was observed at the pupal stage, as compared when they were fed with blowfly puparia-at the first larval stage. While validating thermal summation models, the highest age estimation errors were found for beetles bred at 10 and 12.5 °C (between 21 and 43% for all developmental events). Age estimation errors were on average higher for pupation and eclosion than hatching and first and second ecdyses. While validating the models with specimens fed with different diets, the highest errors were recorded for beetles fed with N. littoralis larvae (22% for the first ecdysis and 33% for the second ecdysis) and Lucilia sp. puparia (32% for pupation and 22% for eclosion). Implications for C. maxillosus use in forensic entomology are discussed.

Modeling the Growth of Black Soldier Fly Hermetia illucens (Diptera: Stratiomyidae): An Approach to Evaluate Diet Quality

The black soldier fly (BSF, Hermetia illucens (Linnaeus), Diptera: Stratiomyidae) is an edible insect widely reared by using various types of organic wastes as its diet. Developing tools to evaluate the growth performance of BSF is crucial for improving its production. In this study, we monitored the daily growth of BSF larvae reared with 10 diets with diverse nutritional quality and compared 7 growth models for quantifying growth performance. We found that BSF generally exhibited an S-shaped growth curve and that the Richards model was the best-fitting growth model. We estimated asymptotic growth limit (W∞) and constructed a time-series curve of absolute growth rate (AGR) by using the Richards model. We used Gaussian functions to estimate AGR parameters (maximum AGR, m; timing of maximum AGR, T; the deviation of AGR, d) to evaluate whether these parameters adequately quantify the growth performance of BSF. Correlation analysis showed that the AGR parameters were mostly independent of W∞ but were correlated with the duration of the larval stage, indicating that W∞ and the AGR parameters respond to different dietary factors. The results of pairwise comparisons showed that the diets rich in carbohydrates and protein had high W∞, m, and d, and early T. The diets with low levels of carbohydrates had low W∞, and the diets with low levels of protein had low m and d and delayed T. We conclude that the parameters estimated by the Richards model could be effective indices for evaluating the growth performance of BSF and their diet quality.

A Review of the Use of Black Soldier Fly Larvae, Hermetia illucens (Diptera: Stratiomyidae), to Compost Organic Waste in Tropical Regions

Hermetia illucens (L., 1758) is a fly of the family Stratiomyidae frequently found in tropical zones. Adult flies are not considered pathogens as they are incapable of biting and feeding thus not transmitting sicknesses to humans. The larval stage feeds off organic matter and offer a rich protein source naturally consumed by animals. The use of black soldier fly (BSF) larvae to treat organic waste is growing around the world. This is especially true for tropical low- and middle-income countries as their favourable climate conditions mean that the BSF technology has significant potential to solve existing problems associated with a poorly developed sanitation infrastructure. In this study, we evaluate the feasibility, benefits and limitations of implementing BSF projects in tropical regions using Belem, in Brazil, as a case study. Black soldier fly prepupae, arising from the waste reduction process, can be used as animal feed. It therefore offers potential to promote regional development, create jobs and dispose of organic waste locally. Legal requirements as outlined in the Brazilian National Policy on Waste offer further incentives. However, more studies are needed to compare BSF waste reduction efficiency and prepupae yield to other technologies such as traditional composting and vermiculture, which can inform the decision-making for implementation of organic waste treatment facilities.

Field Validation of a Development Data Set for Cochliomyia macellaria (Diptera: Calliphoridae): Estimating Insect Age Based on Development Stage

Insect age estimates can be useful for estimating the postmortem interval when certain assumptions are met. Such estimates are based on species-specific development data that are temperature-dependent and variable, and therefore prone to different degrees of error depending on the combination of data sets, calculations, and assumptions applied in a specific instance. Because of this potential error, validating the methods employed is necessary for determining accuracy and precision of a given technique. For forensic entomology, validation of development data sets is one approach for identifying the uncertainty associated with insect age estimates. Cochliomyia macellaria (Fabricius) is a primary colonizer of remains across the United States and is commonly encountered in forensic investigations. A development study for this species was produced for a central Texas, U.S. population; the variation associated with this data set and the pre-appearance interval were previously explored in an ecological model. The objectives of this study were to determine the accuracy of the development data and the validity of the ecological model when applied to immatures of known age developing under field conditions. Results indicate this data set is an accurate predictor of insect age when using development stage, supporting the validity of the ecological model in central Texas. Age predictions made with all stages present in a sample were more accurate than predictions made with the most developed stage in a sample, and estimates of age when using the prepupal stage were overestimated regardless of prediction method, though thermal requirements for total development were similar.

Tolerance of Immature Black Soldier Flies (Diptera: Stratiomyidae) to Cold Temperatures Above and Below Freezing Point

Black soldier flies, Hermetia illucens (L.), consume decaying organic materials at the larval stage and can be used for recycling a variety of biogenic wastes into value-added products. Black soldier flies are normally found in subtropical and warm temperate regions. Cold temperatures may prevent their establishment in colder areas, thus alleviating a concern of their becoming an invasive species. Potentially, cold temperatures can also be used to manipulate the rate of black soldier fly development, which may be needed for timing certain life stages for mass-production needs. In the present study, immature black soldier flies were highly susceptible to freezing. Their survivorship decreased as time spent at -12°C increased from 10 to 60 min. Only ca. 2% of eggs, <1% of larvae, and no pupae survived after 60 min of exposure. Chilling at 4°C also had a significant negative effect that became more pronounced as duration of exposure increased from 24 to 72 h. Only ca. 2% of eggs and second instars and ca. 23% of pupae survived after 72 h. In the same time, >80% of third instars and >90% of fifth instars were still alive following 72 h of exposure. Chilling fifth instars resulted in smaller adults but freezing them for 48 h resulted in bigger adults. Based on these results, black soldier fly is unlikely to establish in areas with long periods of subfreezing winter temperatures. Low temperatures may be used to manipulate development of the late instars, but at a cost of higher mortality.

Managing high fiber food waste for the cultivation of black soldier fly larvae

Increases in global human population are leading to increasing demands for food production and waste management. Insect biomass is a sustainable alternative to traditional animal feeds when insects are produced on lignocellulosic by-products. Resources high in lignocellulose have high carbon to nitrogen ratios and require nitrogen supplementation to accelerate bioconversion. Here we report on studies that examine the influence of nitrogen supplementation of almond hull-based feedstocks on black soldier fly larvae (Hermetia illucens L.) cultivation and composition. Decreasing carbon to nitrogen ratio from 49 to 16 increased larvae harvest dry weight, specific larvae growth, and yield by 36%, 31%, and 51%, respectively. However, the decrease in carbon to nitrogen ratio decreased larvae methionine and cysteine contents by 11% and 13%, respectively. The findings demonstrate that carbon to nitrogen ratio can be managed to enhance bioconversion of lignocellulose to larvae, but that this management approach can reduce larvae amino acid content.

Enhanced bioconversion of dairy and chicken manure by the interaction of exogenous bacteria and black soldier fly larvae

Generation of insects' biomass from lignocellulose rich organic wastes is of significant challenges in reducing the environmental impact of wastes and in sustaining feed and food security. This research looked at the effects of lignocellulotic exogenous bacteria in the black soldier fly (BSF) organic waste conversion system for biomass production and lignocellulose biodegradation of dairy and chicken manures. Six exogenous bacteria were investigated for cellulolytic activity with carboxymethyl cellulose and found that these tested bacterial strains degrade the cellulose. In this study; a co-conversion process using Hermetia illucens larvae to convert the previously studied best mixing ratio of dairy manure (DM) and chicken manure (CHM) (2:3) and cellulose degrading bacteria was established to enhance the larval biomass production, waste reduction and manure nutrient degradation. BSF larvae assisted by MRO₂ (R₅) has the best outcome measures: survival rate (99.1%), development time (19.0 d), manure reduction rate (48.7%), bioconversion rate (10.8%), food conversion ratio (4.5), efficiency of conversion of ingestion (22.3), cellulose (72.9%), hemicellulose (68.5%), lignin (32.8%), and nutrient utilization (protein, 71.2% and fat, 67.8%). By analyzing the fiber structural changes by scanning electron microscopy and Fourier-transformed infrared spectroscopy (FT-IR), we assume that exogenous bacteria assist the BSF larvae that trigger lead to structural and chemical modification of fibers. We hypothesized that these surface and textural changes are beneficial to the associated gut bacteria, thereby helping to larval growth and reduce waste. The finding of the investigation showed that enhanced conversion of DM and CHM by BSF larvae assisted with lignocellulotic exogenous bacteria could play key role in the manure management.