Influence of a propagative plant virus on the fitness and wing dimorphism of infected and exposed insect vectors.

To maximize fitness, plant pathogenic viruses may manipulate their arthropod vectors through direct and indirect (via the host plant) interactions. For many virus-vector-plant associations, insect feeding does not always lead to virus acquisition. In fact, many plant viruses, especially those that propagate into their vectors, are acquired at low rates. Although the majority of insects colonizing an infected plant escape from viral infection, they are still exposed to the indirect effects (i.e. the effect of plant metabolism modification following virus infection). Little information has been reported on the effects of plant viruses on insects that become infected versus those that do not (here referred to as "exposed"). The effect that the Maize mosaic virus (MMV) (Rhabdoviridae) exerts on the fitness and wing dimorphism of the planthopper vector, Peregrinus maidis (Hemiptera, Delphacidae), that developed on leaves from either young or old corn plants was examined. MMV exerted non-consistent to minimal direct effects on developmental time, longevity, nymphal mortality and fecundity. In addition, some small yet significant fitness costs were encountered by exposed planthoppers to escape MMV infection. Furthermore, a significantly higher proportion of macropters over brachypters were produced on MMV-infected old leaves compared with healthy leaves of a similar age. We conclude that the virus influences the dispersal of the vector, promoting a larger production of macropters at the costs of brachypters at a late stage of the plant infection. Because MMV infection in planthoppers did not segregate by wing morphotype, our results indicate that the dispersal of both infected and exposed planthoppers was a likely consequence of the indirect effects of MMV.