Do Plant Viruses Facilitate Their Aphid Vectors by Inducing Symptoms that Alter Behavior and Performance?

Aphids can respond both positively and negatively to virus-induced modifications of the shared host plant. It can be speculated that viruses dependent on aphids for their transmission might evolve to induce changes in the host plant that attract aphids and improve their performance, subsequently enhancing the success of the pathogen itself. We studied how pea aphids [Acyrthosiphon pisum (Harris)] responded to infection of tic beans (Vicia faba L.) by three viruses with varying degrees of dependence on this aphid for their transmission: pea enation mosaic virus (PEMV), bean yellow mosaic virus (BYMV), and broad bean mottle virus (BBMV). BYMV has a nonpersistent motile of transmission by aphids, whereas PEMV is transmitted in a circulative-persistent manner. BBMV is not aphid transmitted. When reared on plants infected by PEMV, no changes in aphid survival, growth, or reproductive performance were observed, whereas infection of beans by the other aphid-dependent virus, BYMV, actually caused a reduction in aphid survival in some assays. None of the viruses induced A. pisum to increase production of winged progeny, and aphids settled preferentially on leaf tissue from plants infected by all three viruses, the likely mechanism being visual responses to yellowing of foliage. Thus, in this system, the attractiveness of an infected host plant and its quality in terms of aphid growth and reproduction were not related to the pathogen's dependence on the aphid for transmission to new hosts.