Plant Virus Transmission by Insects

Abstract Most plant viruses depend on insect vectors for their survival, transmission and spread. They transmit plant viruses by two principal modes, circulative (circulating through the insect's haemocoel, CV) and non‐circulative (carried on the cuticle lining of mouthparts or foregut, NC). Transmissibility and specificity between NC viruses and their vectors depends on the coat protein (CP) of the virus in addition to virus‐encoded helper proteins. Circulative viruses cross the gut, circulate in the haemocoel and cross the salivary glands to render the insect infective. Circulative luteoviruses depend on small CP and the read‐through protein (RTD) for transmission. Electrical penetration graphs have provided evidence on insect feeding behaviour and virus transmission. Recently, studies have shown that viruses can modify vector behaviour in a way that transmission is enhanced. Cultural, physical and novel biotechnological tools can provide virus control by interfering with vector landing and the retention of viruses in their vectors. Key Concepts Most plant viruses rely on insect vectors for survival, transmission and spread. Aphids and whiteflies are by far the most important insects transmitting plant viruses. Some plant viruses are associated to the cuticle of the insect mouthparts (non‐circulative), whereas others are retained in the salivary glands after they circulate through the insect's body (circulative). Some non‐circulative viruses are retained in the common duct of the aphid's maxillary stylets and are inoculated by salivation during brief superficial intracellular probes. Circulative viruses are inoculated during salivation stylet activities in phloem sieve elements. Recent findings in the nature of insect proteins involved in the retention of virus or virus‐encoded helper proteins will help to develop new molecules to interfere with the transmission process.