Feeding behaviour of a virus-vector leafhopper on host and non-host plants characterised by electrical penetration graphs
Many sap-feeders are vectors of plant diseases, acquiring and inoculating pathogens at various stages of the feeding process. In oligophagous species, certain aspects of probing behaviour on hosts and non-hosts may have implications for the range of both pathogens and plants that can be inoculated. We addressed the question of which probing phases (including ingestion) occur on non-host plants in the case of the common leafhopper Psammotettix alienus (Dahlbom) (Hemiptera: Cicadellidae). This species is a pest on cereals, a vector of the Wheat dwarf virus, and possible carrier of other pathogens. It is regarded as oligophagous on grasses, but has been reported also on other plant families. In a combined electrical penetration graph (EPG) video observation study, we aimed to give a description of the waveforms during the probing process. EPG recordings were made on a suitable host, barley, Hordeum vulgare L. (Poaceae), and on two non-host plants, the sedge Carex tomentosa L. (Cyperaceae) and the ragweed Ambrosia artemisiifolia L. (Asteraceae). We demonstrated that P.alienus probes on plants other than Poaceae, including dicotyledons. Univariate and multivariate analyses of general probing variables revealed that total and maximal probe durations were shorter and probing progress less advanced on non-host plants. Waveforms of the pathway phase were stereotypical and statistically not different between the host and non-host plants. On sedge, the waveform signifying insertion through the plant epidermis was shortened but much more frequent, indicating penetration difficulties and retrials. Most importantly, waveforms indicating phloem ingestion were not present on either of the non-host plants. Non-host probing events terminating during the pathway phase suggested that rejection occurred when the stylets were in the mesophyllum. Overall, the EPG signals reflected the unsuitability of A.artemisiifolia and C.tomentosa compared to barley, but the occurrence of probing and the demonstrated level of probing progress imply that pathogen transmission cannot be excluded in the case of many non-host plants and non-specific pathogens.