Due to a swift and continuous growth of the insect rearing industry during the last two decades, there is a need for a better understanding of insect diseases (caused by insect pathogens). In the insect production sector, insect diseases are a bottleneck for every type and scale of rearing system with different degrees of technology investment (i.e. semi-open rearing, closed rearing, industrial production, small-scale farming). In this paper, we provide an overview of insect pathogens that are causing disease in the most common insect species reared or collected for use in food and feed. We also include a few examples of diseases of insect species, which are not (yet) reported to be used as food or feed; those examples may increase our understanding of insect diseases in general and for the development of disease prevention and control measures. We pay special attention to the effect of selected biotic and abiotic factors as potential triggers of insect diseases. We discuss the effect of such factors in combination with other production variables on disease development and insect immunocompetence. Additionally, we touch upon prevention and control measures that have been carried out and suggested up to now for insect production systems. Finally, we point towards possible future research directions with possibilities to enhance the resilience of insect production to insect disease outbreaks.

Opportunistic bacteria are often ubiquitous and do not trigger disease in insects unless the conditions are specifically favorable for bacterial development in a suitable host. In this paper, we isolated and identified a bacterium, Pseudomonas aeruginosa, from the larvae of the giant mealworm Zophobas morio and we studied the possible entry routes by challenging larvae with per os injection and subdermal injection. We also evaluated the effect of exposing groups of larvae to P. aeruginosa inoculated in their feed and the effect of exposing wounded larvae to P. aeruginosa. We concluded that the mortality rate of Z. morio larvae is higher when P. aeruginosa gets in direct contact with the hemolymph via intracoelomic injection compared to a situation where the bacterium is force-fed. Larvae with an open wound exposed to P. aeruginosa presented higher mortality rate compared to larvae with a wound that was not exposed to the bacterium. We documented too, that cannibalism and scavenging were more prevalent among larvae in a group, when P. aeruginosa is present compared to when it is absent. We discuss hereby different aspects related with the pathogen’s entry routes to insects the complexity of pathogen´s transmission in high population densities and different ways to prevent and/or control P. aeruginosa in mass rearing systems.