A Systematic Review on Viruses in Mass-Reared Edible Insect Species

Covert RNA viruses in medflies differ in their mode of transmission and tissue tropism

Numerous studies have demonstrated the presence of covert viral infections in insects. These infections can be transmitted in insect populations via two main routes: vertical from parents to offspring, or horizontal between nonrelated individuals. Thirteen covert RNA viruses have been described in the Mediterranean fruit fly (medfly). Some of these viruses are established in different laboratory-reared and wild medfly populations, although variations in the viral repertoire and viral levels have been observed at different time points. To better understand these viral dynamics, we characterized the prevalence and levels of covert RNA viruses in two medfly strains, assessed the route of transmission of these viruses, and explored their distribution in medfly adult tissues. Altogether, our results indicated that the different RNA viruses found in medflies vary in their preferred route of transmission. Two iflaviruses and a narnavirus are predominantly transmitted through vertical transmission via the female, while a nodavirus and a nora virus exhibited a preference for horizontal transmission. Overall, our results give valuable insights into the viral tropism and transmission of RNA viruses in the medfly, contributing to the understanding of viral dynamics in insect populations.

IMPORTANCE

The presence of RNA viruses in insects has been extensively covered. However, the study of host-virus interaction has focused on viruses that cause detrimental effects to the host. In this manuscript, we uncovered which tissues are infected with covert RNA viruses in the agricultural pest Ceratitis capitata, and which is the preferred transmission route of these viruses. Our results showed that vertical and horizontal transmission can occur simultaneously, although each virus is transmitted more efficiently following one of these routes. Additionally, our results indicated an association between the tropism of the RNA virus and the preferred route of transmission. Overall, these results set the basis for understanding how viruses are established and maintained in medfly populations.

RNA virus diversity and prevalence in field and laboratory populations of melon fly throughout its distribution

Insects have a rich diversity of RNA viruses that can either cause acute infections or persist in host populations without visible symptoms. The melon fly, Zeugodacus cucurbitae (Tephritidae) causes substantial economic losses through infestation of diverse cucurbit and other crops. Of Indomalayan origin, it is now established in many tropical regions of the world. The virome diversity of Z. cucurbitae is largely unknown across large parts of its distribution, including the Indian subcontinent. We have analysed three transcriptomes each of one field-collected and one laboratory-reared Z. cucurbitae population from Bangalore (India) and discovered genomes of ten putative RNA viruses: two sigmaviruses, one chimbavirus, one cripavirus, one noda-like virus, one nora virus, one orbivirus, one partiti-like virus, one sobemovirus and one toti-like virus. Analysis of the only available host genome of a Hawaiian Z. cucurbitae population did not detect host genome integration of the detected viruses. While all ten viruses were found in the Bangalore field population only seven were detected in the laboratory population, indicating that these seven may cause persistent covert infections. Using virus-specific RNA-dependent RNA polymerase gene primers, we detected nine of the RNA viruses with an overall low variant diversity in some but not all individual flies from four out of five Indian regions. We then screened 39 transcriptomes of Z. cucurbitae laboratory populations from eastern Asia (Guangdong, Hainan, Taiwan) and the Pacific region (Hawaii), and detected seven of the ten virus genomes. We found additional genomes of a picorna-like virus and a negev-like virus. Hawaii as the only tested population from the fly's invasive range only had one virus. Our study provides evidence of new and high RNA virus diversity in Indian populations within the original range of Z. cucurbitae, as well as the presence of persistent covert infections in laboratory populations. It builds the basis for future research of tephritid-associated RNA viruses, including their host effects, epidemiology and application potential in biological control.

Detection and Differentiation of Entomopathogenic Serratia spp. to Inform Reintroduction of the Critically Endangered Lord Howe Island Stick Insect Dryococelus australis

Once rodents have been successfully eradicated from Lord Howe Island, Australia, the critically endangered Lord Howe Island stick insect (Dryococelus australis (Montrouzier)) may be reintroduced, a century after it was thought to have become extinct. In captive populations of D. australis, elevated mortalities have been associated with bacterial pathogens. To better define the infectious risk posed by entomopathogens to the reintroduction program, we investigated the bacteria isolated from captive D. australis kept at Melbourne Zoo and on Lord Howe Island and from environmental samples and free-living invertebrates collected on various parts of the island. At Melbourne Zoo, Serratia and Pseudomonas spp. were the bacteria most frequently isolated between 2013 and 2019. Serratia spp. were also the organisms most frequently isolated from insects sampled in April 2019 from the captive population on Lord Howe Island. In addition, Serratia spp. were isolated from a range of environmental samples collected on Lord Howe Island during March-April 2019. These environmental isolates had a broader range of biochemical and molecular characteristics than those obtained from the captive insect populations. A large proportion of these isolates were urease positive and had biochemical profiles previously not described for Serratia spp. This study highlights the need for better surveillance for potential pathogens in understudied regions and sites. We conclude that infections caused by Serratia spp. might pose a problem to the captive breeding program for D. australis but that the risk of introducing novel pathogens to Lord Howe Island through infected insects is low. Our study explores some of the potential risks involved in captive breeding and provides a valuable example of using pathogen surveillance to better inform an invertebrate conservation program.

Dietary and Therapeutic Benefits of Edible Insects: A Global Perspective

Edible insects are gaining traction worldwide for research and development. This review synthesizes a large and well-established body of research literature on the high nutritional value and variety of pharmacological properties of edible insects. Positive benefits of insect-derived products include immune enhancement; gastrointestinal protection; antitumor, antioxidant, and anti-inflammatory capacities; antibacterial activities; blood lipid and glucose regulation; lowering of blood pressure; and decreased risk of cardiovascular diseases. However, the pharmacological mechanisms of these active components of edible insects in humans have received limited research attention. In addition, we discuss health risks (safety); application prospects; regulations and policies governing their production and consumption with a view to promote innovations, intraglobal trade, and economic development; and suggestions for future directions for further pharmacological functional studies. The aim is to review the current state of knowledge and research trends on edible insects as functional ingredients beneficial to the nutrition and health of humans and animals (livestock, aquatic species, and pets).

Outbreak of densovirus with high mortality in a commercial mealworm (Tenebrio molitor) farm: A molecular, bright-field, and electron microscopic characterization

Mealworms are one of the most economically important insects in large-scale production for human and animal nutrition. Densoviruses are highly pathogenic for invertebrates and exhibit an extraordinary level of diversity which rivals that of their hosts. Molecular, clinical, histological, and electron microscopic characterization of novel densovirus infections is of utmost economic and ecological importance. Here, we describe an outbreak of densovirus with high mortality in a commercial mealworm (Tenebrio molitor) farm. Clinical signs included inability to prehend food, asymmetric locomotion evolving to nonambulation, dehydration, dark discoloration, and death. Upon gross examination, infected mealworms displayed underdevelopment, dark discoloration, larvae body curvature, and organ/tissue softness. Histologically, there was massive epithelial cell death, and cytomegaly and karyomegaly with intranuclear inclusion (InI) bodies in the epidermis, pharynx, esophagus, rectum, tracheae, and tracheoles. Ultrastructurally, these InIs represented a densovirus replication and assembly complex composed of virus particles ranging from 23.79 to 26.99 nm in diameter, as detected on transmission electron microscopy. Whole-genome sequencing identified a 5579-nucleotide-long densovirus containing 5 open reading frames. A phylogenetic analysis of the mealworm densovirus showed it to be closely related to several bird- and bat-associated densoviruses, sharing 97% to 98% identity. Meanwhile, the nucleotide similarity to a mosquito, cockroach, and cricket densovirus was 55%, 52%, and 41%, respectively. As this is the first described whole-genome characterization of a mealworm densovirus, we propose the name Tenebrio molitor densovirus (TmDNV). In contrast to polytropic densoviruses, this TmDNV is epitheliotropic, primarily affecting cuticle-producing cells.

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.

Insects as food and medicine: a sustainable solution for global health and environmental challenges

Insects are a significant source of food for millions of people worldwide. Since ancient times, insects in medicine have been contributing to the treatment of diseases in humans and animals. Compared to conventional animal farming, the production of insects for food and feed generates significantly less greenhouse gas emissions and uses considerably less land. Edible insects provide many ecosystem services, including pollination, environmental health monitoring, and the decomposition of organic waste materials. Some wild edible insects are pests of cash crops. Thus, harvesting and consuming edible insect pests as food and utilizing them for therapeutic purposes could be a significant progress in the biological control of insect pests. Our review discusses the contribution of edible insects to food and nutritional security. It highlights therapeutic uses of insects and recommends ways to ensure a sustainable insect diet. We stress that the design and implementation of guidelines for producing, harvesting, processing, and consuming edible insects must be prioritized to ensure safe and sustainable use.

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.

Genome and Genetic Engineering of the House Cricket (Acheta domesticus): A Resource for Sustainable Agriculture

Background: The house cricket, Acheta domesticus, is one of the most farmed insects worldwide and the foundation of an emerging industry using insects as a sustainable food source. Edible insects present a promising alternative for protein production amid a plethora of reports on climate change and biodiversity loss largely driven by agriculture. As with other crops, genetic resources are needed to improve crickets for food and other applications. Methods: We present the first high quality annotated genome assembly of A. domesticus from long read data and scaffolded to chromosome level, providing information needed for genetic manipulation. Results: Gene groups related to immunity were annotated and will be useful for improving value to insect farmers. Metagenome scaffolds in the A. domesticus assembly, including Invertebrate Iridescent Virus 6 (IIV6), were submitted as host-associated sequences. We demonstrate both CRISPR/Cas9-mediated knock-in and knock-out of A. domesticus and discuss implications for the food, pharmaceutical, and other industries. RNAi was demonstrated to disrupt the function of the vermilion eye-color gene producing a useful white-eye biomarker phenotype. Conclusions: We are utilizing these data to develop technologies for downstream commercial applications, including more nutritious and disease-resistant crickets, as well as lines producing valuable bioproducts, such as vaccines and antibiotics.

Insects and Public Health: An Overview

Insects are, by far, the most common animals on our planet. The ubiquity and plethora of ecological niches occupied by insects, along with the strict and sometimes forced coexistence between insects and humans, make insects a target of public health interest. This article reports the negative aspects historically linked to insects as pests and vectors of diseases, and describes their potential as bioindicators of environmental pollution, and their use as food and feed. Both negative and positive impacts of insects on human and animal health need to be addressed by public health professionals who should aim to strike a balance within the wide range of sometimes conflicting goals in insect management, such as regulating their production, exploiting their potential, protecting their health and limiting their negative impact on animals and humans. This requires increased insect knowledge and strategies to preserve human health and welfare. The aim of this paper is to provide an overview of traditional and emerging topics bridging insects and public health to highlight the need for professionals, to address these topics during their work. The present and future role and activities of public health authorities regarding insects are analyzed.

The Variety of Applications of Hermetia illucens in Industrial and Agricultural Areas-Review

Hermetia illucens (Diptera: Stratiomyidae, Linnaeus, 1978), commonly known as the black soldier fly (BSF), is a saprophytic insect, which in recent years has attracted significant attention from both the scientific community and industry. The unrestrained appetite of the larvae, the ability to forage on various organic waste, and the rapid growth and low environmental impact of its breeding has made it one of the insect species bred on an industrial scale, in the hope of producing fodder or other ingredients for various animals. The variety of research related to this insect has shown that feed production is not the only benefit of its use. H. illucens has many features and properties that could be of interest from the point of view of many other industries. Biomass utilization, chitin and chitosan source, biogas, and biodiesel production, entomoremediation, the antimicrobial properties of its peptides, and the fertilizer potential of its wastes, are just some of its potential uses. This review brings together the work of four years of study into H. illucens. It summarizes the current state of knowledge and introduces the characteristics of this insect that may be helpful in managing its breeding, as well as its use in agro-industrial fields. Knowledge gaps and under-studied areas were also highlighted, which could help identify future research directions.

Nutritional Composition, Health Benefits, and Application Value of Edible Insects: A Review

For thousands of years, edible insects have been used as food to alleviate hunger and improve malnutrition. Some insects have also been used as medicines because of their therapeutic properties. This is not only due to the high nutritional value of edible insects, but more importantly, the active substances from edible insects have a variety of biofunctional activities. In this paper, we described and summarized the nutritional composition of edible insects and discussed the biological functions of edible insects and their potential benefits for human health. A summary analysis of the findings for each active function confirms that edible insects have the potential to develop functional foods and medicines that are beneficial to humans. In addition, we analyzed the issues that need to be considered in the application of edible insects and the current status of edible insects in food and pharmaceutical applications. We concluded with a discussion of regulations related to edible insects and an outlook on future research and applications of edible insects. By analyzing the current state of research on edible insects, we aim to raise awareness of the use of edible insects to improve human health and thus promote their better use and development.

Induction of Multiple Immune Signaling Pathways in Gryllodes sigillatus Crickets during Overt Viral Infections

Despite decades of focus on crickets (family: Gryllidae) as a popular commodity and model organism, we still know very little about their immune responses to microbial pathogens. Previous studies have measured downstream immune effects (e.g., encapsulation response, circulating hemocytes) following an immune challenge in crickets, but almost none have identified and quantified the expression of immune genes during an active pathogenic infection. Furthermore, the prevalence of covert (i.e., asymptomatic) infections within insect populations is becoming increasingly apparent, yet we do not fully understand the mechanisms that maintain low viral loads. In the present study, we measured the expression of several genes across multiple immune pathways in Gryllodes sigillatus crickets with an overt or covert infection of cricket iridovirus (CrIV). Crickets with overt infections had higher relative expression of key pathway component genes across the Toll, Imd, Jak/STAT, and RNAi pathways. These results suggests that crickets can tolerate low viral infections but can mount a robust immune response during an overt CrIV infection. Moreover, this study provides insight into the immune strategy of crickets following viral infection and will aid future studies looking to quantify immune investment and improve resistance to pathogens.

Edible Insect Consumption for Human and Planetary Health: A Systematic Review

This systematic review aimed to examine the health outcomes and environmental impact of edible insect consumption. Following PRISMA-P guidelines, PubMed, Medline ProQuest, and Cochrane Library databases were searched until February 2021. Twenty-five articles met inclusion criteria: twelve animal and six human studies (randomized, non-randomized, and crossover control trials), and seven studies on sustainability outcomes. In animal studies, a supplement (in powdered form) of 0.5 g/kg of glycosaminoglycans significantly reduced abdominal and epididymal fat weight (5-40% and 5-24%, respectively), blood glucose (10-22%), and total cholesterol levels (9-10%), and a supplement of 5 mg/kg chitin/chitosan reduced body weight (1-4%) and abdominal fat accumulation (4%) versus control diets. In other animal studies, doses up to 7-15% of edible insect inclusion level significantly improved the live weight (9-33%), reduced levels of triglycerides (44%), cholesterol (14%), and blood glucose (8%), and increased microbiota diversity (2%) versus control diet. In human studies, doses up to 7% of edible insect inclusion level produced a significant improvement in gut health (6%) and reduction in systemic inflammation (2%) versus control diets and a significant increase in blood concentrations of essential and branched-chain amino acids and slowing of digestion (40%) versus whey treatment. Environmental indicators (land use, water footprint, and greenhouse gas emissions) were 40-60% lower for the feed and food of edible insects than for traditional animal livestock. More research is warranted on the edible insect dose responsible for health effects and on environmental indicators of edible insects for human nutrition. This research demonstrates how edible insects can be an alternative protein source not only to improve human and animal nutrition but also to exert positive effects on planetary health.

Safety of frozen and freeze‐dried formulations of the lesser mealworm (Alphitobius diaperinus larva) as a Novel food pursuant to Regulation (EU) 2015/2283

Following a request from the European Commission, the EFSA Panel on Nutrition, Novel Foods and Food Allergens (NDA) was asked to deliver an opinion on frozen and dried formulations from whole lesser mealworm (Alphitobius diaperinus larva) as a novel food (NF) pursuant to Regulation (EU) 2015/2283. The term lesser mealworm refers to the larval form of the insect species Alphitobius diaperinus. The NF comprises the frozen and freeze‐dried formulations of the lesser mealworm as whole or in the form of a paste or powder. Apart from water in the frozen formulations (whole, paste), the main components of the NF are crude protein and fat, besides smaller amounts of digestible carbohydrates and fibre (chitin). The Panel notes that the levels of contaminants in the NF depend on the concentration of such substances in the insect feed. The Panel notes furthermore that the true protein levels in the NF are overestimated when using the nitrogen‐to‐protein conversion factor of 6.25, due to the presence of non‐protein nitrogen from chitin. The applicant proposed to use the NF formulations added as an ingredient to various food products such as cereal bars, pasta, meat imitates and bakery products. The target population is the general population. Additionally, the applicant proposed to use the NF as a food supplement in adults. The Panel notes that, considering that the NF will not be the sole source of dietary protein, and the composition of the NF and the proposed conditions of use, the consumption of the NF is not nutritionally disadvantageous. The submitted subchronic 90‐day toxicity study with the NF as testing material did not raise safety concerns. The Panel considers that the consumption of the NF may induce primary sensitisation and allergic reactions to lesser mealworm proteins and may cause allergic reactions in subjects with allergy to crustaceans and dust mites. Additionally, allergens from the feed may end up in the NF. Allergenicity aside, the Panel concludes that the NF is safe under the proposed uses and use levels.

Expanding the Medfly Virome: Viral Diversity, Prevalence, and sRNA Profiling in Mass-Reared and Field-Derived Medflies

The Mediterranean fruit fly (medfly), Ceratitis capitata, is an agricultural pest of a wide range of fruits. The advent of high-throughput sequencing has boosted the discovery of RNA viruses infecting insects. In this article, we aim to characterize the RNA virome and viral sRNA profile of medfly. By means of transcriptome mining, we expanded the medfly RNA virome to 13 viruses, including two novel positive ssRNA viruses and the first two novel dsRNA viruses reported for medfly. Our analysis across multiple laboratory-reared and field-collected medfly samples showed the presence of a core RNA virome comprised of Ceratitis capitata iflavirus 2 and Ceratitis capitata negev-like virus 1. Furthermore, field-collected flies showed a higher viral diversity in comparison to the laboratory-reared flies. Based on the small RNA sequencing, we detected small interfering RNAs mapping to all the viruses present in each sample, except for Ceratitis capitata nora virus. Although the identified RNA viruses do not cause obvious symptoms in medflies, the outcome of their interaction may still influence the medfly’s fitness and ecology, becoming either a risk or an opportunity for mass-rearing and SIT applications.