Vegetable leafminer

Vegetable leafminer is the larva of an Agromyzid fly that is also called Liromyza sativae. The fly larvae tunnel within leaf tissue which is why they are called leafminers.

Adults

• Small fly-like insects about 1–2mm long.
• Body is yellow and black.

Larvae

• Maggot-like, living in tunnels in the leaf surface.
• Transparent when they first hatch, gradually becoming yellow-orange as they mature.
• Up to 3mm long.

Pupae

• Oval, slightly flattened.
• 1.3–2.3 x 0.5–0.75mm.
• Colour variable, pale yellow-orange, darkening to brown.
• Pupation occurs either on the leaf or on the soil beneath the plant.

Eggs

• Tiny, 0.2–0.3 x 0.1–0.15mm.
• Off-white colour.
• 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. Vegetable leafminer mainly affects leaves.

Plant damage

Symptoms from the larvae's tunnelling and feeding are the most obvious sign. The larvae feed within the layers of the leaf, leaving trails or 'mines' of light green to white 'squiggles' which can be seen on the leaf surface. The tunnels gradually get wider as the larvae grow. Insect faeces are also deposited inside the tunnels which sometimes looks like a blackened stripe at the tunnels edge.

Mining activity by the larvae causes loss of healthy leaf tissue, affecting the plants 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. Vegetable leafminer produces highly convoluted (squiggly) leaf mines and has a broad host range, so if you find leafminer damage on different plant species, then you should suspect vegetable leafminer. Don't hesitate to report it.

Originally from South America, vegetable leafminer has spread across the world into North and Central America, parts of Africa (Cameroon, Sudan, Zimbabwe), Asia (China, India, Oman, Thailand, Yemen), and the Pacific Islands (American Samoa, Cook Islands, French Polynesia, Guam, Micronesia, New Caledonia, Northern Mariana Islands, Samoa and Vanuatu).

Between 2008 and 2015, vegetable leafminer was detected on a number of islands in the Torres Strait. It was detected on the Australian mainland in a remote community on the tip of Cape York Peninsula in 2015; since that time its known distribution remains unchanged.

Vegetable leafminer can cause significant damage to many types of common horticultural crops and ornamental plant species. These include squash, okra, pea, tomato, bean, cabbage, turnip, potato, tobacco, cotton, radish, spinach, watermelon, beet, pepper, alfalfa, clover, vetch and plantain.

• Female flies puncture the leaf surface to feed on sap. The male flies also drink the sap from these wounds.
• The female flies lay eggs in some of the puncture wounds.
• Many eggs can be laid in a single leaf.
• The eggs hatch after 2–5 days depending on the temperature.
• The larvae tunnel inside the leaf tissue creating squiggling tracks in the leaf surface as they move and feed.
• There are 3 larval growth stages (instars).
• The larvae mainly feed on the plant in which the original eggs were laid.
• The time larvae take to transition into pupae, and the pupation period varies depending on the season (e.g. temperature, and food plant).
• Adult flies emerge from the pupae, and are most active at sunrise and during the morning.
• Adult flies mate within 1–2 days of emerging. A single mating event may be sufficient to fertilise all the females' eggs.
• Female flies begin laying eggs soon after mating.
• Generally 10–12 generations may be completed in 1 year.

Queensland grows one-third of Australia's horticultural produce. Valued at more than $2.8 billion per year, the industry employs around 25,000 people (Source: Queensland Farmers Federation).

Vegetable leafminer poses a threat to Queensland's horticulture. Damage caused by vegetable leafminer reduces the growth and development of seedlings and young plants, and can lead to plant death. Poor plant health can result in significantly reduced yield. The presence of unsightly leaf damage in ornamental plants can lead to reduced market value. If this pest were to be detected in a horticultural production area, growers would be affected as domestic and export market access may be disrupted and costly additional control measures may be required.

Home gardeners would also be affected.

The greatest risk of pest spread is by people moving infested plant material or soil. 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 vegetable leafminer, report it to Biosecurity Queensland on 13 25 23 immediately.

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 the Farm biosecurity website

A research, development and extension project for control, eradication and preparedness for vegetable leafminer (2017-2020) is currently underway to identify effective management strategies for the vegetable leafminer. This project has been funded by Hort Innovation, using the vegetable, nursery, melon, and potato 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.

Vegetable leafminer is a declared far northern pest. The far northern biosecurity zones (PDF, 333KB) have been established to prevent the spread of far northern pests.

It is illegal to move:

• a far northern pest such as vegetable leafminer
• far northern pest carriers, such as fruit and vegetables, plants and other plant material, soil or other growing mediums, and appliances or equipment that has come into contact with bee hives, mango plants, banana plants or soil or other growing mediums in which mango, banana or sugarcane has been grown
  • from far northern biosecurity zone 1 to a place outside of that zone
  • from far northern biosecurity zone 2 to a place outside that zone unless it is into far northern biosecurity zone 1.

A biosecurity instrument permit is required to move these items.

You must observe movement restrictions if you are travelling to or around the Cape York Peninsula, or you live there.

For more information about biosecurity instrument permits call the Customer Service Centre on 13 25 23 or email qld.plantquarantine@daf.qld.gov.au.

Your compliance with these regulations will help protect Queensland from vegetable leafminer.