Implications of non-vector herbivores for management of plant viruses in agricultural systems

Pathogens and phytophagous insects are often ecologically disruptive and economically damaging. However, little is known about how these two players interact in complex environments. Here, we examine the mutual effects between a chewing herbivore, the pea leaf weevil (Sitona lineatus) and an aphid-vectored pathogen, pea enation mosaic virus (PEMV). In greenhouse studies, peas (Pisum sativum var. Banner) that experienced herbivory by S. lineatus prior to PEMV inoculation exhibited a significantly higher concentration of virus-related proteins than plants with no history of herbivory. Conversely, S. lineatus individuals feeding on PEMV-infected plants consumed more leaf tissue than individuals feeding on healthy plants, suggesting that infection attenuates the defensive response to chewing herbivores. An observational study in commercial pea fields from eastern Washington state revealed that virus-infected plants experienced significantly higher levels of S. lineatus-related herbivory than healthy plants. These results indicate that attack by a pathogen or phytophagous insect may render a plant vulnerable to a disparate attacker. Additionally, the synergistic interaction between pests and pathogens has important implications for agricultural producers seeking to minimize crop losses.