Interactions between insects and their microbiota affect insect behaviour and evolution. When specific microorganisms are provided as a dietary supplement, insect reproduction, food conversion and growth are enhanced and health is improved in cases of nutritional deficiency or pathogen infection. The purpose of this review is to provide an overview of insect–microbiota interactions, to review the role of probiotics, their general use in insects reared for food and feed, and their interactions with the host microbiota. We review how bacterial strains have been selected for insect species reared for food and feed and discuss methods used to isolate and measure the effectiveness of a probiotic. We outline future perspectives on probiotic applications in mass-reared insects.

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.

The mass rearing of insects for food and feed has emerged as a promising solution to food insecurity, protein production and waste valorisation. While outcomes such as growth and feed conversion efficiency have been examined for mass reared insects, the mechanisms underpinning these outcomes are poorly understood. To optimise the rearing of insects for food and feed and build towards efficient, scalable and productive systems, we must first therefore understand the mechanisms driving productivity and efficiency in common target species. By integrating emerging technologies across disciplines, we can begin to characterise these mechanisms to guide the optimisation of robust and standardised systems for efficient and scalable food and feed production. In this article, we explore opportunities for integrated and interdisciplinary thinking, and the use of emerging technologies to characterise the feeding physiology, digestive processes, microbiome-driven nutritional effects and behavioural regulation of insects commonly used for food and feed. We identify areas of synergy and interaction across research domains and provide a roadmap and call to action to catalyse uptake of these ideas across research and practice. By realising interdisciplinary integration and implementation of emerging technologies, we believe that an urgently required deeper mechanistic understanding of feeding-related processes is possible. This can, in turn, enable precision nutrition, improve system robustness and ensure consistent product quality.

Numerous insect species and their associated microbial pathogens are exposed to elevated CO₂ concentrations in both artificial and natural environments. However, the impacts of elevated CO₂ on the fitness of these pathogens and the susceptibility of insects to pathogen infections are not well understood. The yellow mealworm, Tenebrio molitor, is commonly produced for food and feed purposes in mass-rearing systems, which increases risk of pathogen infections. Additionally, entomopathogens are used to control T. molitor, which is also a pest of stored grains. It is therefore important to understand how elevated CO₂ may affect both the pathogen directly and impact on host-pathogen interactions. We demonstrate that elevated CO₂ concentrations reduced the viability and persistence of the spores of the bacterial pathogen Bacillus thuringiensis. In contrast, conidia of the fungal pathogen Metarhizium brunneum germinated faster under elevated CO₂. Pre-exposure of the two pathogens to elevated CO₂ prior to host infection did not affect the survival probability of T. molitor larvae. However, larvae reared at elevated CO₂ concentrations were less susceptible to both pathogens compared to larvae reared at ambient CO₂ concentrations. Our findings indicate that whilst elevated CO₂ concentrations may be beneficial in reducing host susceptibility in mass-rearing systems, they may potentially reduce the efficacy of the tested entomopathogens when used as biological control agents of T. molitor larvae. We conclude that CO₂ concentrations should be carefully selected and monitored as an additional environmental factor in laboratory experiments investigating insect-pathogen interactions.

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.