Exotic Liriomyza leafminers
In October 2020, the exotic serpentine leafminer (Liriomyza huidobrensis) was detected in NSW. NSW DPI are currently responding to this detection.
Exotic polyphagous leafmining flies of the genus Liriomyza are pests that pose a serious threat to Australian agricultural and horticultural industries. Australia has a number of Liriomyza species already present in Australia, but they do not impact on horticultural production. Leafminers feed in tunnels under the leaf surface — these tunnels cause visible damage which are referred to as ‘mines’.
There are over 300 species of Liriomyza worldwide, with only five of these considered significant pests that are known to attack a wide variety of plants:
- Liriomyza huidobrensis (serpentine leaf miner) — detected in NSW in 2020
- Liriomyza sativae (vegetable leafminer) — detected in Cape York peninsula in 2015, under official control
- Liriomyza bryoniae (tomato leafminer) — not present in Australia
- Liriomyza cicerina (chickpea leafminer) — not present in Australia
- Liriomyza trifolii (American serpentine leafminer) — not present in Australia
The adult flies of Liriomyza species, including exotic and local species present in Australia look very similar. Reliable identification requires examination under a microscope. They are small (1 to 3mm) grey-black flies with yellow markings (Figure 1 and 2).
The larvae of Liriomyza leafminers are yellow to white in colour and feed in the living plant tissue in tunnels beneath the surface of the plant. Larval mining tunnels can be seen on the leaves of infested plants (Figure 3 and 4).
Exotic leafminers leave squiggly white lines on impacted host plants (Figure 5). Heavy tunnelling damage reduces the ability of the plant to photosynthesise which can result in leaf death or premature leaf drop. Heavy infestations can leave stippling damage on plants from the feeding and egg laying sites of the adult females. Mine damage can also reduce crop yield and leave leafy green crops unmarketable due to the tunnelling left behind.
Exotic leafminers have a very wide host ranges, including common weeds in the Asteraceae (sowthistle) and Solanaceae (nightshade) and Fabaceae families. Common vegetable crop hosts include:
Each of these exotic leafminers have different distributions. Liriomyza trifolii is found worldwide except for Australia.
Liriomyza bryoniae is present in Europe, Asia and North Africa and L. cicerina is present in Africa, Europe and the Middle East.
L. huidobrensis is widespread in Africa, Central America, South America, Europe and Asia.
Liriomyza sativae is found almost worldwide, including under official control in Cape York, Australia.
Leafminers are spread through the movement of live host plants containing eggs, larvae, or adults, as well as the movement of pupae via contaminated soil.
Adult leafminers are typically poor fliers, moving only short distances between crops, but can also travel long distances by hitchhiking via human movements or through wind dispersal.
Recognising exotic leafminers
Leafminer damage caused by local leafminer species is generally not distinguishable from an exotic leafminer. Therefore, any suspect leafminer damage should be reported. If you suspect an exotic leafminer infestation, you should report it immediately.
Figure 1 courtesy of Central Science Laboratory, Harpenden , British Crown, Bugwood.org
Figure 2 courtesy of Dr Elia Pirtle, Cesar Australia.
Figure 3 courtesy of Dr Peter Ridland.
Figure 4 courtesy of NSW DPI.
Figure 5 courtesy of Dr Elia Pirtle, Cesar Australia