Parasitoids aid dispersal of a nonpersistently transmitted plant virus by disturbing the aphid vector
Abstract:• Aphids are the major group of insects that vector plant viruses, and they often display a preference for foliage showing disease symptoms. Although this behaviour will increase the numbers of vectors acquiring the pathogen, it will not in itself result in a greater spread of the disease.
• The present study examined how infection of Vicia faba by the nonpersistently transmitted virus bean yellow mosaic virus (BYMV) affected colonization by pea aphids Acyrthosiphon pisum. We then examined how foraging by the hymenopterous parasitoid Aphidius ervi affected aphid settling/movement behaviour and the consequences for dissemination of the virus.
• In Petri dish arenas, aphids colonized discs from BYMV-infected leaves more rapidly than discs from uninfected plants. Reflectance from infected foliage was approximately 20% higher than from uninfected leaves in the green–yellow wavelengths, indicating that aphids might be responding to visual cues from the brighter foliage. Settling was reduced by A. ervi, with the foraging wasps preventing the aphids reaching and/or remaining on the leaf tissue.
• In multiple plant arenas, A. ervi caused a reduction in aphid numbers but also a nine-fold increase in BYMV infection. It is hypothesized that disturbance by the parasitoids resulted in more aphid movement as well as more cases of aphids probing on a BYMV-infected plant and then a new host within the critical time period for successful inoculation to occur. This effect of parasitoids on virus dispersal should be considered in epidemiological models of insect-vectored plant diseases, and also when evaluating the use of natural enemies in biocontrol strategies of insect herbivore/vector pests.