American serpentine leafminer: A threat to all of horticulture

The American serpentine leafminer (Liriomyza trifolii) is a small fly belonging to the family Agromyzidae, that infects plants from 29 plant families including many ornamental, vegetable and legume crops.

Though not yet present in Australia, Liriomyza trifolii poses a significant threat to our horticultural sector.

AUSVEG Biosecurity Officer Madeleine Quirk, shares an update on these pests and the threat it poses to the Australian sector.

Update on American serpentine leafiner

The Research, Development and Extension program for control, eradication and preparedness for vegetable leafminer (MT16004) project was originally developed in recognition of the extensive impact that a related leafminer (Liriomyza sativae) could have on the vegetable, nursery production and melon industries if it were to move into production areas, from Cape York, with no management plan in place.

Since 2017, this RD&E program has been funded by Hort Innovation using vegetable and nursery industry levies, with funds from the Australian Government. Run in conjunction with research provider, Cesar, the project aims to prepare for, and protect against, the spread of the pest throughout Australia’s key growing regions.

Recently, the project has expanded to investigate two closely related leafminers, Liriomyza trifolii and Liriomyza huidobrensis. Though neither species are yet present in Australia, they pose as potential threats to Australia’s nursery production, vegetable, melon and potato industries.

Pest Overview

Adult Liriomyza trifolii can grow between 1 – 1.7 millimetres. The females insert eggs below the leaf surface, which are too small to be seen by the naked eye. Adults generally emerge 7-14 days later.

The lifecycle of this pest varies with temperature, and the larvae feeds internally on living plant tissue particularly impacting plant leaves. The American serpentine leafminer also has a high reproductive rate and has developed resistance to several classes of broad-spectrum insecticides.

Damage from this pest reduces both marketability and crop yield and has resulted in economic losses to growers globally.

Establishment Risk in Australia

Importation of infested ornamental host plants, cut flowers, leafy vegetables and seedlings, poses a major risk for entry into Australia.

Globally, the dispersal and establishment of Liriomyza trifolii has shown to occur rapidly, with populations found on most continents including Europe, Asia, Africa, Central America, the Caribbean, North America, South America and Oceania (American Samoa, Guam, Fiji and Tonga).

The movement of cut flowers and infested chrysanthemum cuttings have played a major role in the spread of this leafminer from its original range in the Americas to other regions in the world.

While not yet present in Australia, many horticultural production regions in Australia have climatic conditions similar to locations overseas where it has established and spread.

It’s a heat-tolerant species, meaning it will thrive in tropical locations, potentially tolerating temperatures near 35°C. It does not adapt as well to cool-climate regions as other leafminers, but it could maintain populations year-round in protected environments such as greenhouses.

Chemical and Biological Control

Managing Liriomyza trifolii incursion can be challenging due to its quick resistance to chemical groups. Applying broad-spectrum insecticides can also result in larger populations as they can often reduce the reservoir of natural enemies.

Plant Health Australia (PHA) is currently looking to obtain insecticide permits for control of Liriomyza trifolii and other Liriomyza leafminers in Australia, as a preparedness measure for growers.

As part of the Research, Development and Extension program for control, eradication and preparedness for vegetable leafminer (MT16004) project, the team are undertaking a global literature review to identify parasitoids in Australia that are known to attack Liriomyza trifolii in other parts of the world.

Any unusual plant pest should be reported immediately to the relevant state or territory agriculture agency through the Exotic Plant Pest Hotline (1800 084 881).

For further information, please contact Greenlife Industry Australia National Biosecurity Manager, John McDonald at email: john.mcdonald@greenlifeindustry.com.au or 07 3277 7900.

The project has been funded by Hort Innovation using the vegetable, nursery, melon and potato research and development levies and contributions from the Australian Government.

This article is reproduced with permission of AUSVEG.

Project Code: MT16004