Several insect species show interaction with a number of bacteria, and these bacterial endosymbionts provide physiological, evolutionary, nutritional, and environmental benefits to the host (insects). To understand these bacterial symbiont–host interactions, different approaches have been used. Fluorescence in situ hybridization (FISH) is one of the approaches which provides a clear visualization of the bacterial endosymbionts residing inside the host tissues or cells. Not only this, but the technique can also be used to validate the findings and help provide a comprehensive understanding relationship between the host and symbionts.