Serpentine leaf miner

PEST PROFILE:

serpentine leaf miner detected in NSW and QLD

BY MADELEINE QUIRK PROJECT OFFICER, AUSVEG

The eggs, larvae and pupae of SLM can be spread through the movement of plant material and soil.

3 SERPENTINE leaf miner damage to squash seedlings.

The serpentine leaf miner (SLM; Liriomyza huidobrensis) is a plant pest from the family Agromyzidae that has a wide host range of plant species including broccoli, beet, spinach, peas, beans, chilli, cucumber, potatoes, cut flowers, melons, and a number of weeds.

The pest can only fly short distances; however, the eggs, larvae and pupae of SLM can be spread through the movement of plant material and soil or potting mix. AUSVEG Project Officer Madeleine Quirk reports. In late 2020, there were several confirmed detections of serpentine leaf miner (Liriomyza huidobrensis) on field-grown vegetables in western Sydney, and in celery and beans in the Fassifern Valley region of Queensland. Following extensive surveillance and assessments on where the pest was found and commodities affected, it was deemed that SLM was not technically feasible to eradicate. This has seen a transition to management for affected industries.

Identification

Adult SLM range from 1.3–2.3mm in length, with black and yellow markings. This pest is difficult to identify with the naked eye, and it is also difficult to distinguish from native leaf miner species. Typically, specialist diagnostics is required to confirm whether an exotic leaf miner is present.

Lifecycle

SLM has an egg, larval, pupal, and adult stage. Female flies lay eggs directly into the leaf, and larvae begin to tunnel through the leaf tissue as they feed. After a number of days, the larvae exit the leaf and pupate in the soil before becoming an adult fly. Under the right conditions, the lifecycle can be completed in as little as two weeks, meaning several generations may be produced within a single crop.

PHOTO © SHANNON MULHOLLAND, NSW DPI PHOTO © CENTRAL SCIENCE LABORATORY , HARPEND E N , B R I 3 SERPENTINE leaf T I S H C R OWN, BUGWOOD. ORG miner adult.

3 SERPENTINE leaf miner stippling damage to choy sum.

Damage

Damage is primarily caused by larvae feeding inside the leaves. Typically, this feeding causes long, narrow, spiralling ‘mines’ which appear as white or grey lines on leaves.

High levels of infestation affect the plant’s ability to photosynthesise, potentially reducing plant growth and crop yields.

At time of writing, SLM had been detected on a total of 35 properties across five NSW regions. Detections in rural NSW were linked to the main outbreak in the Sydney Basin, and affected properties including vegetable farms, nurseries (both vegetable and ornamental), flower importers, home gardens and weeds on roadside verges. Adult females can also Damage is primarily caused by larvae feeding inside the leaves. Vegetable growers were the largest affected group. Thirty-eight plants species from 10 plant families were recorded as hosts, with create damage known as bean, lettuce, spinach, stippling when feeding and chillies, and cucurbits laying eggs. These are small pale particularly affected. green to white circular spots scattered over the leaf surface. Stippling can increase secondary leaf infections, and can affect marketability of produce, especially for leafy vegetables. On November 13, 2020, SLM was detected in Kalbar in the Fassifern Valley after an agronomist reported unusual leaf miner signs and symptoms. Samples were delivered SLM detected in Australia SLM was detected in western Sydney in late October 2020. The New South Wales Department of Primary Industries (NSW DPI), in conjunction with Greater Sydney Local Land Services, launched an emergency response to deal with the outbreak. to the Department of Agriculture and Fisheries, Queensland (DAF QLD) for identification. Those samples were confirmed as SLM on November 18. Surveillance and tracing investigations indicate it is likely that the pest is already established outside the Fassifern Valley. DAF QLD is undertaking

tracing work to determine where plant material has been distributed across south-east Queensland.

As of January 2021, there had been no further detections of SLM in Queensland. Monitoring is continuing in the Fassifern Valley to detect this pest, and to look at what parasitoids are present in the immediate area to help growers make appropriate spray management decisions. Three readily identifiable parasitoids have been found, with others yet to be formally identified.

Climate suitability in Western Australia

SLM is known to have higher tolerance to cooler climates than some other exotic leaf miners, and predictive forecasting work has suggested that establishment risk may be high in many horticultural production regions across Australia. In southern Western Australia, including Perth and regions further south, it is predicted that the climate would be suitable for SLM for more than half the year, increasing the risk of pest establishment. However, in vegetable production regions further north — including Geraldton and Carnarvon — SLM activity would be significantly restricted by desiccation and heat stress, making pest establishment less likely. More information on predicted SLM establishment risk can be requested from Cesar Australia: cesaraustralia. com/contact-us.

3 SERPENTINE leaf miner damage to cucumber. • Avoiding broad spectrum insecticides — do not target leaf miner flies with inappropriate chemicals. Consider soft chemicals when targeting other pests when leaf miner activity is high, as they will harm your beneficial insect population. • Understanding the role of

Integrated pest management crucial

parasitoids — understand the signs of parasitism Taking an integrated approach to the management of SLM will be crucial for the effective control of this pest. to determine if visible leaf mining damage is associated with an active leaf miner population. In response to the recent detections, industry and government have prepared management options for growers, including IPM Inspect your crops regularly for signs of unusual leaf miningactivity. The foundations of an integrated pest and chemical management options. Visit management approach include: dpi.nsw.gov.au for further information. • Monitoring pest activity — apply your own economic thresholds to What can you do? delay and reduce sprays to allow • It can be difficult to distinguish SLM parasitoid populations to build. from native leaf miner species by looking at the insect itself, so visual surveillance should focus on the damage created by the pest • Inspect your crops regularly for signs of plant pests and diseases, including unusual leaf mining activity • Look for leaf miner damage on a wide range of crops • SLM is still a notifiable pest, so suspect samples of SLM infestation should be reported immediately to the Department of Primary Industries or Agriculture by phoning the Exotic Plant Pest Hotline (see more information).

MORE INFORMATION

For more information, visit the following websites: • dpi.nsw.gov.au • daf.qld.gov.au • planthealthaustralia.com.au • ausveg.com.au/mt16004. Any unusual plant pests should be reported immediately to the relevant state or territory agriculture agency through the Exotic Plant Pest Hotline (1800 084 881). For further information, contact AUSVEG on (03) 9882 0277 or science@ausveg.com.au.