THE GUT MICROBIOME ASSOCIATED TO HONEYBEES AND WASTE-REDUCING INSECTS

Abstract

Insects are the most diverse group of animals on Earth and are adapted to a wide range of habitats. They have a remarkable impact on the human life: they include not only human and animal parasites, crop pests, or vectors of human, animal and plant diseases, but also beneficial insects, such as pollinators (e.g. the honeybee Apis mellifera), insects reared to obtain products for the human benefit (e.g. silkworms) or mass-reared insects as food and feed or as biological control agents (e.g. parasitoids or predators). Moreover, since the increase of human population, the growing demand for protein for human and animal consumption is forcing the search of alternative sources: in this scenario insects have been proposed as sustainable rich-protein substrates. For instance, the black soldier fly (BSF, Hermetia illucens) is a promising candidate for the sustainable recycling of biological waste into feedstuff for livestock, poultry and aquaculture in the framework of a circular economy approach (Nguyen et al., 2015; van Huis et al., 2013). The insect evolutionary success and diversification are partially due to the symbiotic relationships that they have established with a wide range of microorganisms. These complex symbiotic interactions include commensal, parasitic and mutualistic relationships (Dale and Moran, 2006). The function commonly attributed to the microorganisms that inhabit the intestinal tract of animals is the depolymerization and breakdown of the diet components, which allow the nutrient supplementation and recycling. Moreover, they also provide detoxification of the toxic diet-components and protection against pathogens and parasites and this underlines the importance of a healthy gut microbiota for the host well-being (Dale and Moran, 2006; Engel and Moran, 2013; Hamdi et al., 2011). At the beginning of this PhD thesis an introductive chapter offers an overview of the current knowledge on the potential application of microorganisms in relation to the management of the emerging insect farming with agricultural, industrial and environmental interest. The insect gut microbiota is influenced by many factors, such as the host diet, developmental stage and genetics, and in the last years researchers have been addressed many efforts to elucidate their impact on the host gut microbiota, mainly considering insect pests, parasites or vectors of diseases (Montagna et al., 2015a; Vacchini et al., 2017). Moreover, the importance to characterize factors, such as the oxygen concentration, pH and redox potential status, existing within the insect gut compartments has been only recently recognized and, hence, not so much work has been performed so far in this direction. Indeed, the insect gut includes aerobic and anaerobic niches, passing through microaerophilic habitats, and compartments characterized by acidic, neutral or basic conditions, even in the same digestive tract (Engel and Moran, 2013). Understanding the drivers that shape the microbial diversity in the insect gut microbiota is pivotal in comprehending the…