Biosecurity Alert - Liriomyza trifolii (Burgess) syn. Liriomyza alliovora. American serpentine leafminer

Pest
Liriomyza trifolii (Burgess) syn. Liriomyza alliovora.

American serpentine leafminer

Synonyms:
Broad bean leafminer, Californian leafminer, Celery leafminer, Chrysanthemum leafminer 

Date
22 July 2021

Location
Northern WA and Torres Strait (QLD)

Situation

The exotic plant pest American serpentine leafminer Liriomyza trifolii has recently been found infesting plant hosts in Kununurra, Western Australia (March 2021) and Thursday Island (Torres Strait), Queensland (May 2021). The Northern Australia Quarantine Service (NAQS) have reported multiple detections of American serpentine leafminer in the Torres Strait and in Kununurra, Western Australia. Further detections of American serpentine leafminer have also occurred in the Northern Peninsula Area of Cape York Peninsula (QLD) which are still undergoing confirmatory identification.  Surveillance is still being conducted to determine the distribution of this pest in both WA and QLD.

The samples of suspected leafminer species in WA and QLD were identified as American serpentine leafminer (Liriomyza trifolii) with a 99%+ genetic match between the Kununurra and Torres Strait specimens. This identification was confirmed during the week of 9 July 2021 using genetic testing and morphological identification techniques.

The Consultative Committee on Emergency Plant Pests (CCEPP) met on 19 July 2021 to discuss the detections. The committee agreed that American serpentine leafminer is considered an emergency plant pest under the Emergency Plant Pest Response Deed (EPPRD), but further information was needed to determine whether it was technically feasible to eradicate.  More detailed surveillance and diagnostic data was thought to be valuable to inform the committee’s consideration of technical feasibility of eradication and the appropriate course of action. This information will be provided by WA for the committee’s consideration.

American serpentine leafminer poses a serious threat to Australia’s horticulture, nursery production, and agricultural plant industries. Severe infestations of American serpentine leafminer may result in premature leaf drop, poor growth, and reduced crop yields. Australia considers it a National Priority Plant Pest.

American serpentine leafminer are flies in the genus Liriomyza and can be confused with other species within the genera e.g. the recently detected Serpentine leafminer in NSW.  Larvae feed internally on plant tissue, particularly the leaf, creating the classic mining trails that are associated with infestation. Larvae then pupate in the substrate beneath the plants and hatch out as flies which then lay eggs on surrounding host plants perpetuating the reproductive cycle and increasing damage. Damaged plants commonly have reduced yield and in some cases are completely destroyed. Like many Liriomyza spp. this pest is known to carry and develop insecticide resistance making it difficult to manage.

It has a wide host range of plant species which includes beans, celery, chrysanthemum, cucumber, gerbera, gypsophila, lettuce, onion, potato, tomato, peanuts, soybeans, lentils, lupins, faba beans, chickpeas and many more.

For useful identification information and images please use the on-line pest identification platform www.pestid.com.au

Biology
Liriomyza trifolii is a pest in greenhouses and warm climates, though it may seasonally become a pest in cooler climates. It is highly polyphagous and has been recorded on 25 plant families. The most important crops attacked are beans, carrot, celery, Chinese wax gourd, chives, chrysanthemum, cucumber, edible gourds, eggplant, gerbera, gypsophila, hibiscus, lettuce, onion, pea, pepper, potato, pumpkin, spinach, squash, tomato and watermelon.

The American Serpentine Leafminer lifecycle varies with host and temperature, at 20°C to 30°C a lifecycle can take between 12 to 28 days, while at 15°C the lifecycle takes up to 54 days. Adults can survive temperatures down to 12°C but appears to stop feeding and laying eggs. Pupa can survive freezing temperatures but die before emergence at temperatures above 32°C. Ten or more generations can be produced in a year.

Eggs: microscopic (0.24 mm long), oval and creamy white, laid inside the leaf. Hatch in 2 to 7 days.

Larva: a legless maggot about 3 mm long, change from colourless to pale yellow-orange as they grow through three instar (larval) stages. When mature they cut a slit in the leaf and drop to the ground to pupate (puparium).

Pupa: oval, segmented and slightly flattened, pale yellow-orange to golden brown between 1.3 mm to 2.3 mm in length. Adults emerge after 7 to 14 days.

Adults: Are about 2 to 3 mm in length, their bodies are mostly yellow in colour. The head and antennae are bright yellow. The upper surface of the thorax is matte dark grey to black. Their scutellum is also light yellow. Adults 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 unassisted or assisted by the wind.

Damage: Eggs are laid singly by puncturing the leaf, which can cause stippling and allow entry of bacteria and pathogens. The larvae of American serpentine leafminer tunnel in the chloroplast-containing spongy mesophyll layers, disrupting photosynthesis. The larval leaf mine varies in form depending on the host but when adequate space is available the mine is long, narrow and not greatly widening towards the end. Damage caused by a single larva is minimal, however when large populations are present, they are capable of destroying leaves and affecting the growth of plants.

Trade
There are no expected trade impacts from American serpentine leafminer, either internationally or domestically, aside from those currently in place on plant movement in the Torres Strait and Northern Peninsular Area of QLD and potential controls in Northern WA.

Report and submit samples
All growers are encouraged to report any suspect signs of leaf mining in host plants to the . Instructions will be given on how to collect and submit samples for identification.

For further information contact the GIA National Biosecurity Manager John McDonald email: john.mcdonald@greenlifeindustry.com.au or call 07 3277 7900.