The yellow mealworm, Tenebrio molitor, is currently one of the most important insect species produced for livestock feed and human consumption. High-density rearing conditions make the risk of disease and infections by parasitic symbionts a challenge in the mass production of these insects. However, certain symbionts are beneficial and should be favoured in order to promote healthy insect populations. Knowledge of parasitic symbionts and their management is essential for the insect rearing industry and its associated research. Here we review the documented microbial infectious agents, invertebrate parasites, and beneficial symbionts occurring in T. molitor. Furthermore, we discuss detection, prevention, and treatment methods for disease management in T. molitor production systems to inform future management and decision making in T. molitor rearing.

As the insects for food and feed industry grows, a new understanding of the industrially reared insect microbiome is needed to better comprehend the role that it plays in both maintaining insect health and generating disease. While many microbiome projects focus on bacteria, fungi or viruses, protists (including microsporidia) can also make up an important part of these assemblages. Past experiences with intensive invertebrate rearing indicate that these parasites, whilst often benign, can rapidly sweep through populations, causing extensive damage. Here, we review the diversity of microsporidia and protist species that are found in reared insect hosts and describe the current understanding of their host spectra, life cycles and the nature of their interactions with hosts. Major entomopathogenic parasite groups with the potential to infect insects currently being reared for food and feed include the Amoebozoa, Apicomplexa, Ciliates, Chlorophyta, Euglenozoa, Ichtyosporea and Microsporidia. However, key gaps exist in the understanding of how many of these entomopathogens affect host biology. In addition, for many of them, there are very limited or even no molecular data, preventing the implementation of molecular detection methods. There is now a pressing need to develop and use novel molecular tools, coupled with standard molecular diagnostic methods, to help unlock their biology and predict the effects of these poorly studied protist parasites in intensive insect rearing systems.

Insect mass-rearing is a rapidly expanding industry for the production of protein for food and feed. These highly productive artificial rearing environments can expose insects to a range of biotic and abiotic stressors, including insect pathogens, which may result in population crashes. Interactions between insect pathogens with multiple stressors can exacerbate the effects of individual pathogens on host insects. However, reliable predictions on the combined effects of individual stressors based on mechanisms of action are lacking within the field of insect pathology. We review how ecotoxicological modelling of multiple stressors can be applied to mass-reared insect systems and discuss the importance of standardization across research fields investigating multiple stressors. Important considerations in multiple stressor terminology, experimental design, endpoints and analysis of results are discussed to improve understanding of multiple stressors and their impact on insects for food and feed. This is essential for ensuring optimal rearing conditions for mass-reared insect populations.

This study provides a comprehensive taxonomic description of a microsporidian parasite infecting crickets, Gryllus bimaculatus and G. assimilis. Our analysis includes gross pathology, histopathology, spore ultrastructure, parasite development cycle, single gene phylogenies, and phylogenomic comparisons. We introduce a new taxon, Albopleistophora grylli n. gen. n. sp., characterised by its unique developmental stages within a sporophorous vesicle, leading to the formation of mature spores measuring 5.7 x 2.8 mu m. Although prevalent in commercial cricket cultures, this parasite seemed to have limited effects on cricket survival. Indeed, microsporidia exposure and density assays with the host G. bimaculatus, only revealed density as a significant factor affecting the crickets' survival. Nevertheless, exposure showed significant effect on the crickets' emergence time, where exposed crickets emerged as adults earlier than unexposed individuals. Moreover, exposure to the parasite increased the faeces production and weight gain in cricket males. However, neither exposure nor density significantly impacted the females' fecundity. The absence of spores in non-exposed cricket groups suggested a horizontal transmission, highlighting the importance of controlled rearing practices to eliminate this microsporidium in control groups. The well-known anti-microsporidian drug 'fumagillin' was studied with a higher microsporidia dose of exposure to evaluate any improvement in cricket survival, without showing any significant differences between exposed and unexposed groups. Our findings underscore the nuanced dynamics of host-microsporidia interactions and emphasise the need for ecological context in understanding microsporidian impacts. Even if non-dangerous for its host, monitoring of this parasite seems crucial due to its potential zoonotic transmission by its close phylogenomic relation to human-infecting microsporidia species.

This study investigates the taxonomy of the gregarine parasite Leidyana gryllorum (Cuénot, 1897) Watson, 1916, originally described from Acheta domesticus Linnaeus, 1758, and its putative synonym L.erratica (Crawley, 1907) Watson, 1916, from Gryllus pennsylvanicus Burmeister, 1838. While an 18S rRNA gene sequence exists for L.erratica, L. gryllorum lacked molecular characterisation. Here, a combined morphological and genomic approach was applied to resolve their relationship. Hybrid genome sequencing (Illumina and Nanopore) of specimens from A. domesticus produced a 15.5 Mbp assembly. Specific 18S primers designed from this assembly amplified a fragment showing 91% similarity to L.erratica, supporting their distinction as separate species. Genome annotation revealed metabolic pathway reduction consistent with eugregarine adaptations. Data mining of NCBI WGS, TSA, and SRA datasets identified additional Leidyana-like 18S rRNA gene sequences across multiple Grylloidea hosts, forming a L.gryllorum subclade distinct from L.erratica and indicating a broad host range. This integrated approach enhances the understanding of gregarine evolutionary diversity and host associations in Orthoptera.

The mass rearing of insects for food and feed is increasing significantly, but it presents challenges in detecting and characterizing pathogens which may cause severe economic losses. Much attention is placed on detecting viruses, bacteria and fungi; however, other significant entomopathogens remain overlooked, such as protist and microsporidian parasites. This study employed Nanopore sequencing to explore and phylogenetically analyse microsporidian and protist parasites in reared insects. Using group-specific primers and amplicon pooling strategies, we successfully amplified and sequenced a key protist group (Gregarinasina), microsporidia and fungal pathogens from insect host DNA, providing data for their future detection. Our approach generated novel molecular data, enabling the inference of small subunit and long subunit rRNA phylogenies which enhance the understanding of the evolutionary origin of these parasites. Furthermore, we highlight potential shortcomings of currently available primers and provide new Gregarine-specific primers to aid in further research of these overlooked entomopathogens. This research demonstrates the effectiveness of third-generation sequencing technologies in improving diagnostic tools and advances the study of pathogen biodiversity within economically important insect hosts.