Incursion Preparedness: Anticipating the Arrival of the Plant Pathogen Xylella Fastidiosa and its Insect Vector Homalodisca Vitripennis in Australia

Anna Rathe

    Research output: ThesisDoctoral Thesis

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    The glassy-winged sharpshooter, Homalodisca vitripennis, is an important insect
    vector of the xylem-limited bacterial plant pathogen Xylella fastidiosa which causes diseases in numerous host plants including food and feedstock crops, ornamentals and weeds. Both the pathogen and the vector are native to the Americas and are considered to be highly invasive. Neither has been detected in Australia to date so the general aim of this study was to prepare for a possible incursion event of either species. The wine and table grape industries are particularly concerned about the arrival of H. vitripennis because of the potential economic impact on these important Australian commodities. Past H. vitripennis invasions, such as that which occurred in French Polynesia where the H. vitripennis population exploded, have demonstrated the need for rapid detection and containment of an incursion. This requires (i) knowledge of H. vitripennis feeding and oviposition host plant species and, (ii) X. fastidiosa host plant species and (iii) identification of regions in Australia that have climatic and environmental conditions conducive to establishment. These regions and host plant species can then be targeted for monitoring in order to detect an incursion of the pathogen or vector at an early stage. This study provides information on the suitability of Australian native plants as hosts of X. fastidiosa and H. vitripennis. Previous CLIMEX modelling has shown that much of the Australian mainland has temperatures suitable for survival of the insect and pathogen, however a range of other requirements must be satisfied for invasion success to occur. In order to assess the ability of H. vitripennis to survive inter-continental flights, survival of H. vitripennis under conditions simulating an aircraft hold and options for its biological control in Australia were also investigated.

    To determine whether the plants from the twelve Australian native plant genera of interest (Acacia, Banksia, Callistemon, Correa, Eremophila, Eucalyptus, Grevillea, Hakea, Leptospermum, Melaleuca, Prostanthera and Swainsona) can host X. fastidiosa, a survey of existing native Australian vegetation in landscape
    surrounding Riverside, California, USA was undertaken. None of the 200 samples
    assayed using PCR and bacterial culture was positive. A greenhouse inoculation
    study was completed to determine host status, persistence of the pathogen over
    winter, population size and systemic spread. Xylella fastidiosa was detected in
    Hakea petiolaris, Swainsona galegifolia, Grevillea alpina and Leptospermum
    laevigatum nine months after mechanical inoculation. Systemic spread 10cm from the point of inoculation was also observed in these species so they can be considered hosts of the bacterium. The pathogen could not be recovered from any of the other Australian species. The four host species may act as reservoirs from which further spread of the pathogen could take place should it reach Australia and may be useful indicator plants for early detection.

    Twelve Australian plant species of interest were investigated for suitability as H. vitripennis feeding, oviposition and nymph development hosts. All twelve species were shown to be feeding hosts in the greenhouse in a no-choice study. Field surveys did not show evidence of adult or nymph feeding on Melaleuca laterita, Callistemon viminalis, Prostanthera ovalifolia, Correa schlentalii, and G. lanigera. An oviposition host status field study was conducted with citrus, a favoured oviposition host, as the control. With the exception of four of the Australian native species (C. viminalis, G. lanigera, M. laterita and P. ovalifolia) tested, all were found to be oviposition hosts under elevated pest pressure. A greenhouse study was conducted to determine nymph survival and the development time to adulthood on each of the Australian native plant species of interest. First instar H. vitripennis nymphs developed to adulthood on Acacia cowleana, L. laevigatum, G. lanigera, S. galegifolia and Vitis vinifera control plants although there were high nymph mortality rates on all species. Insects on A. cowleana, G. lanigera and S. galegifolia developed faster than the V. vinifera control insects. Egg parasitism by the Mymarid parasitoid Gonatocerous ashmeadii was observed on all Australian oviposition host plants indicating that introduction of this parasitoid to Australia could be considered should H. vitripennis establish in Australia.

    Greenhouse acquisition studies showed that insects free from X. fastidiosa were able to acquire the pathogen after feeding from infected S. galigifolia, H. petiolaris, G. alpina plants and grape control plants which subsequently passed the infection on to grape seedlings although both acquisition and transmission rates were very low. Transmission from infected L. laevigatum was not observed.

    Laboratory studies were undertaken to determine the risk of air transport as a
    possible H. vitripennis invasion pathway. It is thought that the most likely means of introduction is via egg masses in plant tissue of imported nursery stock or live
    insects transported in the cargo hold of aircraft. A study conducted under various cargo hold temperatures (5 °C, 11 °C and 22 °C) indicated that female adults are able to survive 24 hours at each temperature without food and – to a much lower extent - go on to reproduce successfully when re-introduced to a suitable ovipostion host plant.

    A nation-wide assay of known host plant species in Australia in 2011 failed to detect X. fastidiosa infection, adding to the evidence that Australia is currently free from this bacterium. If it were to invade Australia without the important insect vector H. vitripennis, it is possible that xylem feeding Australian native insects from the Auchenorryncha subfamily may act as vectors.

    The results of the host status, invasion pathway and natural enemy research are presented with the implications of these findings discussed and placed in an
    Australian invasion context. The results have practical applications and
    recommendations are presented to alter Australian biosecurity practices and policy. These recommendations may assist to prevent or rapidly contain and eradicate an incursion of either H. vitripennis or X. fastidiosa, or both, in Australia.
    Original languageEnglish
    QualificationDoctor of Philosophy
    Awarding Institution
    • Charles Sturt University
    • Pilkington, Leigh J., Co-Supervisor
    • Gurr, Geoffrey, Co-Supervisor
    Award date01 May 2012
    Place of PublicationAustralia
    Publication statusPublished - 2012


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