Detection of a new exotic plant pest is never good news but knowing that strong preparation for such a detection has been undertaken can sweeten this bitter pill.
The current situation
A high priority exotic plant pest, the serpentine leafminer (Liriomyza huidobrensis; family Agromyzidae), has recently been found in Western Sydney. This detection has activated the formal government-industry consultative process for considering if eradication is technically feasible.
At this point, NSW Department of Primary Industries and Greater Sydney Local Land Services are conducting surveillance to determine the extent of the incursion.
The serpentine leafminer has a wide host range that includes onion and garlic (Alliaceae); celery (Apiaceae); beetroot and spinach (Amaranthaceae); capsicum, tomato, eggplant, potato and petunia (Solanaceae); melons, cucumber and marrow (Cucurbitaceae); lettuce, aster, marigold, chrysanthemum, gerbera and zinnia (Asteraceae), beans, faba bean and peas (Fabaceae); and gysophila (Caryophyllaceae). The host range also extends into non-commercial crops.
Adults create holes to feed on leaves and to lay eggs inside leaves, creating ‘stippling’ damage. Upon hatching, larvae tunnel through leaves, feeding and creating thick white trails, called ‘leaf mines’. Most damage occurs at the larval stage. Larvae then emerge and pupate in the soil.
Adult flies emerge from pupae, can mate 24 hours after emergence and live for 15 to 30 days depending on conditions. They are not very active flyers and may be seen walking rapidly with short flights to adjacent leaves.
Overseas experience has shown that this species can greatly impact plant vigour through larval feeding. Crop losses of 50% or more have been recorded for several crops including spinach, capsicum and celery in vegetable producing areas around the world. Potato is a particularly favoured crop, with crop losses of 30% to >70% having been reported in Indonesia, Argentina, Chile and Peru. Reduced marketability of crops through aesthetic damage is also a factor.
However, this doesn’t need to be the story in Australia.
These high economic impacts seen oversees are universally associated with the destruction of the major natural enemies of serpentine leafminer, tiny parasitoid wasps, by excessive use of non-selective insecticides. It has been demonstrated repeatedly overseas that parasitoid wasps are a core component of successful leafminer management, and we know that Australia is already home to abundant parasitoid species, including several species already well known for providing effective control of leafminer overseas.
IPM programs, which avoid the use of broad-spectrum insecticides and rely upon economic thresholds to reduce numbers of sprays applied, will be paramount for successful management of this pest.
Creating an exotic leafminer knowledge bank
After detection of the vegetable leafminer (Liriomyza sativae), in the Torres Strait and Cape York Peninsula, the Hort Innovation funded initiative ‘Research, development and extension program for control, eradication and preparedness for vegetable leafminer’ was launched in 2017.
Since the project commencement, our multi-organisation project team has been researching exotic agromyzid leafminer species in a bid to improve the preparedness of multiple primary industries. Three species in particular have been the focus of our research and extension: vegetable leafminer, American serpentine leafminer (Liriomyza trifolii), and serpentine leafminer.
It’s not often that biosecurity preparedness work can be completed by using a test case in country. However, presence of the vegetable leafminer on the mainland, within quarantine zones at the far north tip of Queensland, has given our project team a unique chance to test surveillance and diagnostic methodologies for this species over 2017-2020, and to learn about its biology and impact on the ground. Importantly, methodologies developed during the project can be extended to monitoring for other exotic agromyzid leafminers, such as the serpentine leafminer.
The project has also resulted in development of a large number of surveillance, awareness and preparedness resources for government and industry. These resources can be found on the AUSVEG website here.
For a crash course in exotic leafminer risk, biology and identification spend some time watching the project video series. Learn more about exotic leafminers and preparedness work in Australia in this video, or for more in depth information access this educational webinar series.
In 2020, as we finalise our project activities, we are able to contribute our accumulated knowledge, resources and methodologies to aid in this incursion response. This a great example of the importance of preparedness.
Stay alert for the serpentine leafminer
The primary method of serpentine leafminer spread is likely to be through movement of eggs and larvae on live plant material and cut flowers. Pupae may spread with soil. Adults can disperse by wind, but can also be spread via human assisted movement such as on goods, aircraft, vehicles and plant material.
You can report any signs of leaf mining in vegetables to the Exotic Plant Pest Hotline on 1800 084 881. Photos of damage and leafminers can be sent to email@example.com.
The strategic levy investment project RD&E program for control, eradication and preparedness for Vegetable leafminer (MT16004) is a part of the Hort Innovation Vegetable and Nursery Funds. This project has been funded by Hort Innovation, using the vegetable and nursery research and development levies and contributions from the Australian Government. Hort Innovation is the grower-owned, not-for-profit research and development corporation for Australian horticulture.