American serpentine leafminer

American serpentine leafminer (Liriomyza trifolii) is the larva of small flies belonging to the family Agromyzidae.

The fly larvae tunnel within leaf tissue, which is why they are called leafminers.

Adults

• Small fly-like insects, 1–2mm.
• Black with yellow head and yellow spots on thorax.
• Brownish-yellow antennae with dark end segments.

Larvae

• Transparent when they first hatch before turning pale yellow-orange then solid yellow-orange as they mature.
• Develop inside leaf tissue and vary in size but can reach up to 3.2mm.
• Form irregular serpentine mines, which tend to be restricted by the leaf veins.

Pupae

• Pupation occurs externally to the leaf usually in the soil below the plant and sometimes on the leaf surface.

Eggs

• Slightly translucent and off-white.
• Tiny, barely visible to the naked eye.
• Laid under the leaf surface.

Plant stage and plant parts affected

Host plants of any age and stage of growth can be infested but young plants are most susceptible. American serpentine leafminer mainly affects leaf tissue.

Plant damage

Typically, infestation of plants is first noticed by the presence of mines in the surface of leaf tissue. Leaf mines are usually white with black and dried brown areas. Leaf mines are typically serpentine or irregular in shape and increase as the larvae mature.

Mining activity by the larvae causes loss of healthy leaf tissue, affecting the plant's ability to photosynthesize. Disease causing fungi and viruses can also be introduced into the plant through feeding puncture wounds made by the adult flies. In severe infestations leaves can wilt and die, causing defoliation.

Similar damage could be caused by other leaf mining insects that are present in Queensland. Serpentine leafminer (L. huidobrensis) and vegetable leafminer (L. sativae) also produce highly convoluted (squiggly) leaf mines and have a broad host range.

If you find leafminer damage on a variety of plant species at the same location, you should report it.

The American serpentine leafminer is thought to have originated from North America and has since spread to Africa, Asia, Central and South America and Europe.

American serpentine leafminer is not currently widely established in Australia. Since March 2021, there have been multiple detections in the Torres Strait, in Far North Queensland (Northern Peninsula Area of Cape York Peninsula), and in Kununurra, northern Western Australia.

American serpentine leafminer affects a wide range of common horticultural crops and ornamental plant species.

They have been found to seriously affect solanaceous crops (such as potato, tomato and eggplant), as well as crops in the Asteraceae, Cucurbitaceae and Fabaceae families.

Several generations may be produced in a year. Female flies pierce the leaf surface to lay eggs inside. Eggs hatch in 2–5 days depending on temperature and larvae mine the leaf tissue. The larvae primarily feed on the plant in which the eggs are laid. Larvae leave the plant to pupate.

American serpentine leafminer damage reduces crop marketability and yield, resulting in economic losses to growers.

If the American serpentine leafminer were to become established in Australia without control mechanisms in place, it would have a significant effect on horticultural production.

Home gardeners would also be affected.

The greatest risk of pest spread is by people moving infested plant material, soil or associated packaging.

Adult flies may also hitchhike in vehicles, machinery or aircraft.

The adult flies are not very strong flyers. The flies usually walk quickly over leaves and fly short distances to move between leaves or nearby plants. Strong winds may assist adult flies to fly further afield.

Inspect your plants regularly for the presence of leaf mines.

Look for leafminer damage on a variety of plant species or unusual or severe leafminer leaf damage.

If you suspect you have found American serpentine leafminer in other areas of Queensland, report it to Biosecurity Queensland on 13 25 23.

Protect your farm from plant pests and diseases:

• Potato growers biosecurity manual (PDF, 2.9MB)
• Biosecurity manual for the nursery production industry (PDF, 3.1MB)
• Biosecurity induction manual for Bundaberg horticultural farms (PDF, 1.3MB)
• Protect your farm from emergency plant pests
• Understand good farm biosecurity
• Visit Farm biosecurity.

Explore the outcomes of the Hort Innovation-funded research, development and extension project for control, eradication and preparedness for vegetable leafminer (2017-2020).

Under Queensland's Biosecurity Act 2014, there are 2 far northern biosecurity zones covering Torres Strait and the northern Cape York Peninsula. The Far Northern Biosecurity Zone 2 begins north of Coen and ends in a line between Mapoon and Heathlands in the northern Cape. The Far Northern Pest Biosecurity Zone 1 continues above Zone 2 and spans the 5 townships of the Northern Peninsula Area as well as Torres Strait. Plant material cannot move out of Zone 1 or south out of Zone 2 without a permit.

Learn how to apply for a biosecurity instrument permit.

Movement between the Torres Strait and mainland Australia is also controlled under the Commonwealth's Biosecurity Act 2015. Federal legislation specifies that plant material cannot move from the Torres Strait Permanent Biosecurity Monitoring Zone into mainland Australia without a permit.