The hidden roles of insect symbiotic viruses in pest control and arbovirus transmission.

With the advance of metatranscriptomic sequencing, an increasing number of symbiotic viruses have been recognized in insects. These insect symbiotic viruses not only modulate key aspects of insect biology, including physiology, fecundity, development, and behavior, but also influence the vector competence of arthropods for transmitting arboviruses. The majority of such vectors belong to the orders Hemiptera and Diptera, which transmit a wide spectrum of plant and animal arboviruses. Although insect symbiotic viruses usually replicate exclusively within insect cells, several symbiotic viruses have also been detected in insect secretions and even in host plants, indicating they may have more profound functions than we originally thought. In this review, we synthesize current knowledges on the hidden roles of insect symbiotic viruses across three key dimensions: their impact on insect adaptation to host plants, as reflected in fitness, feeding behavior, dispersal capacity, and resistance traits; their regulation of vector competence for the transmission of both plant and animal arboviruses; and their emerging application as biotechnological tools for the delivery of double-stranded RNA, small-interfering RNA, or recombinant proteins to control viral diseases in agriculture and public health.