A non-vector herbivore indirectly increases the transmission of a vector-borne virus by reducing plant chemical defenses

Vectors and viruses exist in communities consisting of many interacting species. Although the cascading effects of predators or parasitoids on disease spread via direct effects on vectors have been investigated, little is known about the effects of other free-living species in communities on the transmission of vector-borne viruses via indirect (host-plant mediated) effects on vectors. In the present study, we used a food web consisting of tomato plants (Solanum lycopersicum), two tomato herbivores (the vector whitefly, Bemisia tabaci, and the non-vector two-spotted spider mite, Tetranychus urticae), and a whitefly-vectored plant virus (Tomato yellow leaf curl virus, TYLCV) to study how T. urticae may affect TYLCV transmission by B. tabaci via host-plant mediated effects on B. tabaci. We found that T. urticae infestation promoted B. tabaci feeding and thereby increased TYLCV transmission to tomato plants. These increases were associated with T. urticae-induced reductions in two f...