Changes in green peach aphid responses to potato leafroll virus-induced volatiles emitted during disease progression

Previous research has shown that green peach aphids, Myzus persicae (Sulzer), preferentially settle on leaflets of potato plants (Solanum tuberosum L.) infected with potato leafroll virus (PLRV) compared with sham-inoculated controls, at least in part because of aphid responses to volatile cues from the plants. The prior work used plants 4 wk after inoculation. In this study, aphid emigration from the vicinity of leaflets of PLRV-infected plants at 2, 4, 6, 8, and 10 wk after inoculation was compared with emigration from leaflets of sham-inoculated control plants. For the bioassay, 30 aphids were placed directly above a test leaflet on screening to exclude gustatory and tactile cues and in darkness to exclude visual cues. The numbers emigrating were recorded every 10 min for 1 h. Volatile organic compounds (VOCs) were collected from the headspace of the test plants, quantified, and compared among treatments. In bioassays with leaflets of upper nodes of the plants, aphid immigration rates were significantly lower from leaflets of PLRV-infected plants than from sham-inoculated plants at 4 and 6 wk after inoculation, but not at 2, 8, and 10 wk after inoculation. In bioassays with leaflets from lower nodes, emigration did not differ between PLRV-infected plants and sham-inoculated plants at any stage in the infection. Volatile compounds detectable in the headspace of intact plants at 2, 4, and 8 wk after inoculation (or sham inoculation) changed with plant age and with disease progression, potentially explaining behavioral responses of the aphids.