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Simple Summary: The black soldier fly is rapidly becoming the most extensively farmed insect on the planet. The number of relevant publications is also growing exponentially. This review covers all the most recent, available publications on the subject of how this insect interacts with microbes. It consolidates the information on the insect's gut microbiome and identifies species that could be used as probiotics for fly farmers. The review affirms past results that black soldier fly larvae do rely on gut microbes for digestion, but do not have a globally conserved core microbiome. Bacterial probiotics for the larvae show promise, but the most common gut microbe genera have so far not been tested as probiotics. This is a promising direction for future investigations. Black soldier fly (Hermetia illucens, BSF) is farmed worldwide to convert organic waste into usable biomaterials. Studies on the larval microbiome have been carried out to check for symbiotic or pathogenic microbes and their respective functions and fates. Some studies tested these microbes for industrial applications, while others tested the effects of exogenous microbes as probiotics or for substrate pre-processing to improve larval fitness, bioconversion rates, or nutritional qualities. This review examined all peer-reviewed literature on these topics to consolidate many disparate findings together. It followed the PRISMA guidelines for scoping reviews. The results found no evidence of globally conserved core microbes, as diet strongly correlated with gut microbiome, but some genera appeared most frequently in BSF larval guts worldwide regardless of diet. The gut microbes undoubtably assist in digestion, including pathogen suppression, and so microbial probiotics show promise for future investigations. However, the common gut microbes have not been explored as probiotics themselves, which would be a promising direction for future work. The impacts of BSF bioconversion on pathogens varied, so each rearing facility should investigate and manage their pathogen risks independently. The data summarized in this study provide useful reference points for future investigations into BSF–microbe interactions. [ABSTRACT FROM AUTHOR]

Bergmann's rule states that organisms should be smaller in warmer climates. This traditionally implied warmer latitudes, but also applies to warmer eras, as forming due to climate change. Integrating spatial and temporal ecology (chronoecogeography) can help us understand and predict how different species respond to environmental changes over time. However, study results can be misinterpreted if researchers do not take steps in the data collection or analysis stages to account for range shifting or non-monotonic patterns. Multiple variables can cause an organism's geographic and recent temporal size clines to differ significantly, as seen in a review in this article, and these cannot easily be modeled. Range shifting can affect Bergmann's rule modeling, especially regarding effects from climate change, and this article suggests methods to account for this when incorporating the dimension of time into climate change-focused ecogeographic research. [ABSTRACT FROM AUTHOR]

The sparse descriptions of the stick insect (Phasmatodea) digestive system as reported/provided in the literature are highly contradictory. This paper describes the digestive systems of several families of Phasmatodea (Timematidae, Heteropterygidae, Diapheromeridae, Pseudophasmatidae, and Phasmatidae) plus the gut microbiome of these and one other (Phylliidae) to both verify past findings and provide a general description of the Phasmatodea alimentary canal. The constrictions imposed by this anatomy on phasmid gut microbiology, its connections to recently released Phasmatodea transcriptomes, and how it differs from the anatomy of related orders in the Polyneoptera are discussed. All Phasmatodea have ridged proventriculi lined or covered with small spines. Anterior projections of the midgut, sometimes described as gastric caeca, are only found in Euphasmatodea and often obscure the proventriculus. We define the cardia as the complex of foregut and midgut tissue where the type II peritrophic matrix is produced. Appendices of the midgut are an autapomorphy for Phasmatodea, but Timema have fewer and larger appendices relative to body size. We suggest caeca-like projections and the loss of large, proventricular teeth are apomorphies of Euphasmatodea. We identify a possible facultative symbiosis in Eucalyptus-feeding species that requires further study.

BackgroundStick and leaf insects (Phasmatodea) are an exclusively leaf-feeding order of insects with no record of omnivory, unlike other "herbivorous" Polyneoptera. They represent an ideal system for investigating the adaptations necessary for obligate folivory, including plant cell wall degrading enzymes (PCWDEs). However, their physiology and internal anatomy is poorly understood, with limited genomic resources available.ResultsWe de novo assembled transcriptomes for the anterior and posterior midguts of six diverse Phasmatodea species, with RNA-Seq on one exemplar species, Peruphasma schultei. The latter's assembly yielded >100,000 transcripts, with over 4000 transcripts uniquely or more highly expressed in specific midgut sections. Two to three dozen PCWDE encoding gene families, including cellulases and pectinases, were differentially expressed in the anterior midgut. These genes were also found in genomic DNA from phasmid brain tissue, suggesting endogenous production. Sequence alignments revealed catalytic sites on most PCWDE transcripts. While most phasmid PCWDE genes showed homology with those of other insects, the pectinases were homologous to bacterial genes.ConclusionsWe identified a large and diverse PCWDE repertoire endogenous to the phasmids. If these expressed genes are translated into active enzymes, then phasmids can theoretically break plant cell walls into their monomer components independently of microbial symbionts. The differential gene expression between the two midgut sections provides the first molecular hints as to their function in living phasmids. Our work expands the resources available for industrial applications of animal-derived PCWDEs, and facilitates evolutionary analysis of lower Polyneopteran digestive enzymes, including the pectinases whose origin in Phasmatodea may have been a horizontal transfer event from bacteria.

The stick insects or phasmids (Phamsatodea) have a series of pyriform ampulles with long, thin filaments on the posterior end of their midgut referred to as the "appendices of the midgut." Found only in phasmids, their function had never been determined until now. Their similarity to the Malpighian tubules, which are ubiquitous insect organs of excretion, suggested a similar function. To differentiate between the appendices and the Malpighian tubules and compare functional differences between the two tissue types, vital staining (the injection of histological stains into living organisms) was done in conjunction with light and scanning electron microscopy in multiple phasmid species. The results showed that the appendices originated in the basal phasmids (Timematidae) and grew more numerous in derived species. The appendices stain selectively, notably failing to pick up the indicators of the two known systems of invertebrate excretory function, indigo carmine and ammonium carmine. Appendices sequester stains in the ampule portion before eliminating the compounds into the midgut. We conclude by confirming that the appendices do have an excretory function, but one unlike any other known in invertebrates. Their function is likely cation excretion, playing a role in calcium regulation and/or organic alkaloid sequestration. The appendices must thus be considered distinct organs from the Malpighian tubules.

(1) Background. At subzero temperatures, water crystallizes on ice nucleation agents. Researchers have identified ice-nucleating microbes (INMs) in insect digestive tracts that can raise the insect's supercooling point, causing freezing at higher temperatures but slower rates. For freeze-tolerant insects, such gut microbes should allow for slower freezing away from tissues and higher survival rates. For freeze-susceptible insects, however, such microbes could cause a fatal freeze at higher temperatures, and could possibly be used as biocontrol. (2) Methods. A first-ever scoping review was carried out of research on insect-associated INMs, from observational studies attempting to isolate these microbes, to experimental studies applying them and checking for increased mortality. (3) Results. Relatively few research groups have studied insect-associated INMs in any capacity. (4) Conclusions. Several authors hypothesized that such microbes are probably abundant, and their contribution to ice nucleation activity in insects is under-reported. Biocontrol assays using ice-nucleating microbes showed promise, but a risk to non-target organisms has been experimentally confirmed. Future surveys of insect–microbe interactions using molecular tools are likely to reveal new examples, if not new microbe species capable of ice nucleation. [ABSTRACT FROM AUTHOR]

Abstract Background Little is known about the Phasmatodea gut microbial community, including whether phasmids have symbiotic bacteria aiding in their digestion. While symbionts are near ubiquitous in herbivorous insects, the Phasmatodea’s distinctively thin body shape precludes the gut enlargements needed for microbial fermentation. High-throughput sequencing was used to characterize the entire microbiota of the fat bodies, salivary glands, and anterior and posterior midguts of two species of walking stick. Results Most bacterial sequences belonged to a strain of Spiroplasma (Tenericutes) found primarily in the posterior midgut of the parthenogenetic species Ramulus artemis (Phasmatidae). Beyond this, no significant differences were found between the R. artemis midgut sections or between that species and Peruphasma schultei (Pseudophasmatidae). Histological analysis further indicated a lack of bacteriocytes. Conclusions Phasmids are unlikely to depend on bacteria for digestion, suggesting they produce enzymes endogenously that most other herbivorous insects obtain from symbionts. This conclusion matches predictions based on phasmid anatomy. The role of Spiroplasma in insects warrants further study.