Rearing insects for food and feed is a rapidly growing industry, because it provides excellent opportunities for a sustainable approach to animal protein production. Two fly species, the black soldier fly (BSF) and the house fly (HF), naturally live in decaying organic matter (e.g. compost), and can thus be effectively reared on organic rest streams from the food and agricultural industry. The adoption of these insects as mini-livestock on microbially rich substrates, however, requires us to address how we can safeguard insect health under mass-rearing conditions. In this review, we discuss what is known about the innate immunity of insects in general, especially focusing on a comparative approach to current knowledge for the two dipteran species BSF and HF. We also discuss environmental factors that may affect innate immunity in mass-rearing settings, including temperature, insect densities and diet composition. Furthermore, we address the role of the microbiome in insect health and the associations of these fly species with detrimental or beneficial microbes. Finally, we present a perspective on important open scientific questions for optimizing the mass rearing of these insects with respect to their health and welfare.

During the last decade the potential of insects for human nutritional protein is increasingly recognised. Direct consumption of insects contributes to a reduction of the ecological footprint of human food production and is claimed to have health benefits. An alternative is feeding poultry (broilers and layers) with insect-derived protein. This offers several additional advantages, e.g. a more extensive use of (new sources) of organic by-products of food industry for insect production. Implementation of a People-Planet-Profit (PPP) sustainable way of utilising these opportunities requires the development of sustainable business models. Such business models need to be based on the opportunities of insect-derived protein in feeding poultry but should also include the risks associated with insect-derived protein for feeding poultry. This article explores the insect-fed poultry production value chain through an interdisciplinary approach. First, the essential features of this value chain are described. Then, an inventory and classification is made of the main opportunities and risks of this value chain. Finally, the opportunity-risk trade-offs are discussed, as well as their implications for developing sustainable business models. We conclude that for PPP-sustainable business models, management of the asymmetric trade-offs between opportunities and risks related to possible contamination of organic by-products used as substrate for insect production should receive prime attention. Implications for organising the value chain are discussed.