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Wednesday, 24 March 2021 17:30

Gaining knowledge about likely Xylella fastidiosa vectors in New Zealand

Written by  Jim Herdman
Project leader Jessica Vereijssen from Plant & Food Research putting out an insect sticky trap. Photo  Mette Nielsen. Project leader Jessica Vereijssen from Plant & Food Research putting out an insect sticky trap. Photo Mette Nielsen.

Seven vineyards, in Hawke’s Bay and Canterbury, are taking part in a new biosecurity research project examining the presence of potential insect vectors of Xylella fastidiosa, the bacterium which causes Pierce’s disease of grapevines, in vineyards and the adjoining natural vegetation.

Xylella fastidiosa (X. fastidiosa) is transmitted by obligate xylem-feeding (i.e, only feeding on xylem) insects which spread the bacterium by uptaking it when feeding on an infected host plant, and pass it on to the next plant. Insects such as sharpshooter leafhoppers and spittlebugs are known to be vectors overseas. One key insect vector in grapevine is the glassy-winged sharpshooter, which is not present in New Zealand. This insect is also on the New Zealand Winegrower’s (NZW) most unwanted list. Spittlebugs are present in New Zealand, and the status of cicadas as vectors of X. fastidiosa needs more research.

The research project will advance the understanding of endemic and native insect vectors in New Zealand that could potentially transmit X. fastidiosa. In New Zealand, only spittlebugs and cicadas are obligate xylem feeders, reducing the number of insect species to focus on in this project.

The project aims to deliver new knowledge on the distribution of potential endemic insect vectors of X. fastidiosa, as well as their host plants, seasonality, and movement between the native and productive estate, using vineyards (Canterbury and Hawke’s Bay), summerfruit (Otago) and citrus orchards (Kerikeri) as case studies. The project team may also undertake gut content analysis of xylem feeders to determine what plants they have been feeding on, and tracking of adult cicadas in the native estate to establish any patterns in their movement. The information obtained through the research will be incorporated into the Ministry for Primary Industries (MPI) and Department of Conservation (DOC) risk assessments and industry response plans for an incursion of X. fastidiosa. This will have short and long-term benefits for New Zealand’s biosecurity system, informing where to concentrate early detection surveillance efforts, and where it might be necessary to manage imports of certain plant species for a more efficient response to a potential X. fastidiosa incursion.

Field work

Field trial work started in November. Three NZW members - Pegasus Bay, Ataahua Vineyard, and Fancrest Estate - are taking part in the Canterbury region, and four in Hawke’s Bay: Black Barn Vineyards, Waiana Estate, Pernod Ricard and Te Mata Estate. Invertebrate sampling on these vineyards will be undertaken by staff from Plant & Food Research  (PFR) and Manaaki Whenua – Landcare Research.

Sampling in the field consists of sweep netting, beat sampling, and the use of sticky traps and intercept traps. Any insects collected during the netting and beat sampling process are put in plastic zip-lock bags. In the laboratory, spittlebugs and cicadas are separated from the other insects, individually placed in ethanol and identified to family, genus, and species level where possible, or sent for identification by the MPI Plant Health and Environment Laboratory. Some of the spittlebugs and cicadas are used to develop molecular identification techniques for these insects. Sticky traps and intercept traps are send to the laboratory at PFR Lincoln, where spittlebugs and cicadas caught are counted.

The scientists will use the data from field and laboratory experiments for modelling spread of the spittlebugs and cicadas in different landscapes. Using scenarios the project team hopes to understand the risk profiles for these landscapes and inform MPI, DOC and horticultural industries.

The Xylella insect vector project is being led by Jessica Vereijssen of PFR, as part of the Better Border Biosecurity (B3) science collaboration (b3nz.org.nz). Working within co-innovation principles, other participants include NZW, Manaaki Whenua – Landcare Research, DOC, MPI, the Xylella Action Group, Citrus NZ, Summerfruit NZ, Kiwifruit Vine Health, and New Zealand Plant Producers Incorporated. Discussions are also being held with leaders in the PFR’s Growing FuturesTM research programme to explore synergistic work and sharing of invertebrate samples.

Xylella fastidiosa – a Most Unwanted plant pathogen

Pierce’s disease is a disease of grapevines that is not present in New Zealand but could be imported through infected plant material. The disease is caused by the bacterium X. fastidiosa, which multiplies in the grapevine’s xylem vessels, clogging them and preventing the plant from transporting water from roots to canopy. This results in stunting, dieback, and eventual death. Pierce’s disease is fatal to grapevines, killing mature vines in a period of one to three years after infection. Once vines are infected, there is no way to treat the disease.

All Vitis vinifera varieties are susceptible to Pierce’s disease, but they vary in longevity and productivity after infection. Grape varieties such as Sauvignon Blanc and Chardonnay are very susceptible to the disease, with a short time between infection and death. Varieties such as Cabernet Sauvignon are less susceptible.

As well as grapevines, X. fastidiosa has at least 370 known host plants, several of which are economically and culturally important in New Zealand. Consequently, New Zealand has strong biosecurity measures in place, seeking to prevent the entry of X. fastidiosa into the country

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