9 - Insect Immunity to Viruses

Abstract

This chapter appraises the antiviral mechanisms against viruses that replicate in insects, including genetic resistance, physical and physiological barriers to infection, cellular and subcellular inhibition, humoral immunity, and developmental resistance. Some practical applications of this knowledge for management of agricultural pests and vector-borne disease have also been highlighted. Two extremes of insect–virus interactions have been explored: insect viruses that are lethal to the host (e.g., the baculoviruses) and viruses for which transmission is contingent upon the host's survival. Insect viruses are ingested with food material, enter the host tissues via the gut epithelium, and replicate in this tissue, and in some cases in other tissues as well. Baculovirus replication ultimately leads to the death of the host insect followed by lysis of the cadaver and release of virus into the environment. The virus has to negotiate a series of barriers for successful infection, such as the pH and contents of the gut, penetration of the peritrophic membrane, entry into and infection of gut epithelial cells, and some other immunity. There are numerous examples where one of these barriers in specific species or strains of mosquitoes arrested the development of a particular arbovirus. Although significant advances have been made in understanding the mechanisms and countermechanisms involved in antiviral immunity, there are still many gaps in the knowledge of insect immunity to viruses. From a practical standpoint, some of the means by which insect viruses have overcome physiological barriers to infection, such as the use of enzymes that degrade the PM, can potentially be exploited for insect pest control. Overall, the study of insect immunity to viruses promises to provide many fruitful future avenues for exciting research.