Abstract
The emergence of emerging and reemerging infectious diseases throughout history has been the product of the interaction of infectious agents, immunity, selective pressure, and environmental factors. The origin of the viral ancestors remains controversial, the debate remains whether the viruses existed before their host cells, evolved as molecular structures that adapted to the intracellular development or of the cells that infected or housed them as hosts. The nature of the viruses could propose a hypothetical evolutionary model based on the way they parasitize cells and the way they fuse with their host cells. So far there are no “universal” viral genes that have not allowed the hypotheses of the “common viral ancestor” to be conclusive. Insects have a special role in understanding viral evolution and how they became pathogens, suggesting a coevolutionary scenario of colonization that would initially allow the survival of viruses and later an ecological niche required for the cycle of virus replication. The coevolution of viruses and defense systems of hosts represents a fundamental role in the evolution of both viruses and host cells, a kind of arms race between viruses and hosts, and the deescalation of that war could explain the coexistence of viruses and hosts. Viruses are playing an important role in the understanding of cell evolution and have earned the right to be included in the tree of life. The aim of this chapter is to review the viral evolution and the insects as host.