Symbiosis is close and often long-term association between two or more different biological species. An endosymbiont is any organism that lives within the body or cells of another organism, i.e., forming an endosymbiosis. The endosymbiotic bacteria of insects are categorized as primary symbionts (obligate) and secondary symbionts (facultative). Symbionts provide an array of functions to its host starting from growth, development and survival to other diverse functions. Endosymbionts also give protection to its host against the biotic and abiotic stress. Some of the major functions of the endosymbionts are defense toward pathogens and parasites, influence on insect-plant interaction, adaptation to environment, impact on population dynamics and pesticide detoxification. Endosymbionts are currently known to manipulate host reproduction in three ways: through male-killing (MK), feminisation and cytoplasmic incompatibility (CI). The other approaches like endosymbionts as attractants, in paratransgenesis approach (Trojan horse), increasing the susceptibility of insect pests to viral disease than protecting them, use of endosymbionts to reduce pesticide resistance development etc. can be used as a novel methods and as component of integrated pest management. Manipulating symbionts may be exploited to improve pest control and finding out more about insects and their microbial associates will be both fascinating and useful. Establishment of endosymbionts trans-infections to globally significant agricultural pests is needed. Development of genetically modified endosymbionts and their application of transgenesis to control of agricultural pests and vector-borne diseases will open for new vistas for managing of notorious agricultural pests and diseases.