The mass production of insects is rapidly expanding globally, supporting multiple industrial needs. However, parasite infections in insect mass-production systems can lower productivity and can lead to devastating losses. High rearing densities and artificial environmental conditions in mass-rearing facilities affect the insect hosts as well as their parasites. Environmental conditions such as temperature, gases, light, vibration, and ionizing radiation can affect productivity in insect mass-production facilities by altering insect development and susceptibility to parasites. This review explores the recent literature on environment-host-parasite interactions with a specific focus on mass-reared insect species. Understanding these complex interactions offers opportunities to optimise environmental conditions for the prevention of infectious diseases 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.

We examined the contents of nutritional importance, i.e., amino acids, fatty acids and minerals of different developmental stages of drones of two honey bee subspecies, namely Apis mellifera carnica and A. m. mellifera. The results revealed that, in general, individual amino acid amounts and therefore the total protein increased along with the developmental stages of the drones. No statistically significant differences were found between the same developmental stages of the two subspecies. The reverse, i.e., a decrease with developmental stage occurred in relation to the fatty acid composition. Most of the minerals were higher at advanced developmental stages. Overall, the high protein content (31.4–43.4%), small amount of fat (9.5–11.5%) and abundance of minerals such asiron and zinc, make drones a suitable nutritional resource. Even though nutrient content, especially protein, was higher in the pupae than the prepupae, we propose prepupae also as a commercial product based on their higher biomass production. Provided standard production protocols maintaining hygiene and safety will be adhered to, we propose that drone honey bees can be utilized as human food or animal feed.

Dead sporulating female fly cadavers infected by the house fly-pathogenic fungusEntomophthora muscaeare attractive to healthy male flies, which by their physical inspection may mechanically trigger spore release and by their movement create whirlwind airflows that covers them in infectious conidia. The fungal artillery ofE. muscaeprotrudes outward from the fly cadaver, and consists of a plethora of micrometric stalks that each uses a liquid-based turgor pressure build-up to eject a jet of protoplasm and the initially attached spore. The biophysical processes that regulate the release and range of spores, however, are unknown. To study the physics of ejection, we design a biomimetic ‘soft cannon’ that consists of a millimetric elastomeric barrel filled with fluid and plugged with a projectile. We precisely control the maximum pressure leading up to the ejection, and study the cannon efficiency as a function of its geometry and wall elasticity. In particular, we predict that ejection velocity decreases with spore size. The calculated flight trajectories under aerodynamic drag predict that the minimum spore size required to traverse a quiescent layer of a few millimetres around the fly cadaver is approximately 10 µm. This corroborates with the natural size ofE. muscaeconidia (approx. 27 µm) being large enough to traverse the boundary layer but small enough (less than 40 µm) to be lifted by air currents. Based on this understanding, we show how the fungal spores are able to reach a new host.

The yellow mealworm (Tenebrio molitor) is a promising insect species for mass-rearing for the production of feed and food. In mass-production systems, insects may be exposed to abiotic stressors such as heat stress as well as potentially lethal pathogens. To ensure mass-reared T. molitor populations are healthy and productive there is a need to understand both the risks, and potential benefits of heat stress, on the fitness of insects and their susceptibility to pathogens. In this study, we investigated the effects of a short (2 h) or a long (14 h) heat stress (38 °C) exposure on the susceptibility and the immune responses of T. molitor larvae exposed to a fungal pathogen (Metarhizium brunneum). Larvae were exposed to the pathogen either immediately or five days after the heat stress treatments. The development of heat stressed larvae and their offspring was also assessed. A short heat stress immediately before exposure to M. brunneum increased the survival probability of T. molitor larvae, which correlated with increased antibacterial activity in the hemolymph. The exposure of larvae to short, or long heat stresses five days before pathogen exposure did not affect their survival, despite a temporary lowered body mass gain of heat stressed larvae. However, heat stressed larvae showed decreased hemocyte concentrations when exposed to M. brunneum. We also found an increased body weight in larval offspring of females that had been exposed to a short heat stress as larvae themselves. These findings demonstrate the importance of understanding the effects of heat stress in the long-term. The beneficial effects of heat stress on pathogen susceptibility in T. molitor and the negative effects on body mass gain are only transient, whereas negative effects on immune response (hemocyte concentrations) persist over an extended period.

Entomophthoralean fungi are insect pathogenic fungi and are characterized by their active discharge of infective conidia that infect insects. Our aim was to study the effects of temperature on the discharge and to characterize the variation in the associated temporal pattern of a newly discovered Pandora species with focus on peak location and shape of the discharge. Mycelia were incubated at various temperatures in darkness, and conidial discharge was measured over time. We used a novel modification of a statistical model (pavpop), that simultaneously estimates phase and amplitude effects, into a setting of generalized linear models. This model is used to test hypotheses of peak location and discharge of conidia. The statistical analysis showed that high temperature leads to an early and fast decreasing peak, whereas there were no significant differences in total number of discharged conidia. Using the proposed model we also quantified the biological variation in the timing of the peak location at a fixed temperature.