A comprehensive review on transmission mechanism of plant viruses by insects

Most plant viruses depend on insect vectors for their survival, transmission, and spread. These viruses are transmitted by insects through two principal modes: circulative and non-circulative. In the circulative mode, the virus circulates through the insect’s haemocoel (CV), whereas in the non-circulative mode, the virus is carried on the cuticle lining of the insect's mouthparts or foregut (NC). The transmissibility and specificity between non-circulative viruses and their vectors depend on the coat protein (CP) of the virus, in addition to virus-encoded helper proteins. Circulative viruses cross the insect's gut, circulate in the haemocoel, and eventually cross the salivary glands to render the insect infective. For circulative luteoviruses, small coat proteins and the read-through protein (RTD) are essential for transmission. Electrical penetration graphs have provided evidence on insect feeding behavior and virus transmission. Recent studies have shown that viruses can modify vector behavior to enhance transmission. Cultural, physical, and novel biotechnological tools can provide virus control by interfering with vector landing and the retention of viruses in their vectors.