Microbes through its symbiotic relationship between the host and their invaded organisms, owes a major part in nature as well as the evolutionary processes. Insects are the most diversified fauna with stable surveillance in innumerable ecological niches. Many among those act as secondary symbionts as well. These symbiotic connotations originated more recently and can be ephemeral. In some cases, the direct contact with the host also is not needed in a population for these organisms to survive. Because when the primary symbionts transfer the genes directly from mother to progeny, the secondary symbionts do it through several means. This chapter reviews the association between insect gut microbiomes and their interactions with the environment. Recent insights and potential applications of the insect gut microbiome will provide a metagenomic thorough knowledge of the microbial census in the insect gut.