Liriomyza species – leaf min ing flies
Background
The fly genus Liriomyza (Diptera: Agromyzidae) consists of hundreds of species, most of
which are leaf miners; their larvae tunnel within leaf tissue forming damaging and
disfiguring mines. The majority of species are either host -specific or are restricted to a
small group of plants that are related to each other. However, a few species are h ighly
polyphagous, able to feed on many different types of plants, and have become agricultural
and horticultural pests in many parts of the world. These include four species that are
listed in the plant quarantine legislation of various countries, includi ng the European Union:
L. bryoniae (tomato leaf miner) , L. huidobrensis (South American leaf miner or serpentine
leaf miner) , L. sativae (vegetable leaf miner ) and L. trifolii (American serpentine leaf
miner) . The wide host range of these pests means that they will attack both vegetable
crops and ornamental plant production.
Figure 1. Adult Liri omyza sativae © Crown copyright courtesy Fera Science Ltd
Plant Pest Factsheet
Geographical D istribution
There are 41 species of Liriomyza found in the UK, including L. bryoniae which has long
been established as an important pest of tomatoes grown under glass in England, and is
found across Europe and Asia, as well as parts of North Africa. The other three regulated
species, L. huidobrensis , L. sativae and L. trifiolii , all orig inate from the Americas, but have
been spread around the world in recent decades, particularly to parts of Africa, Asia and
the Pacific, by the trade in plants and plant products. None have become established in
the UK, although all three are regularly int ercepted on imported plant material at ports -of -
entry. To date, L. sativae has not been found in Europe, although it has been introduced
into both Israel and Turkey. Both L. huidobrensis and L. trifolii are now established in parts
of the European continen t and are widespread in some countries, particularly those with
suitable climates.There have been a number of outbreaks in the past three deca des of L.
huidobrensis and L. trifolii , attacking crops under protected cultivation in England, but
these have alw ays been eradicated.
There are a number of other recognised pest species of Liriomyza , but all have a much
more restricted host range ; these are also intercepted on imported plant material at ports -
of -entry from time to time, but pose a less substantial th reat to UK agriculture and
horticulture.
Host Plants
The four regulated species of Liriomyza are all highly polyphagous with numerous different
plant hosts recorded for each species. These include both vegetable crops and plants
used in ornamental flower p roduction.
Description
Adult Liriomyza flies are all small (2 – 3 mm in length) and, from above, are seen to be
largely black with yellow areas on the head and sides. Their most distinctive characteristic
is a yellow spot on the back, on the scutellum (Figure 1), although this colour combination
is not unique to Liriomyza species. The different species of Liriomyza can only be
identified with certainty by means of laboratory examination.
The larvae are typical, legless, fly maggots, but never more than 3 mm lo ng. They can be
off -white or orange -yellow, depending on species, but are seldom seen as they remain
within the mine. Pupae , are more cylindrical, about 3 mm long, and can vary in colour from
yellow through to brownish -black (Figure 2) .
Figure 2 . Liriomy za huidobrensis puparia © Crown
copyright courtesy Fera Science Ltd
Figure 3. Liriomyza trifolii mine and feeding
punctures on chrysanthemum © Crown copyright
courtesy Fera Science Ltd
Figure 4 . Liriomyza sativae mine on cucumber ©
Crown copyright courtesy Fera Science Ltd
Figure 5. Adult Liriomyza on a sticky trap © Crown
copyright courtesy Fera Science Ltd
Biology
Eggs are laid within the leaf tissue and are not visible to the naked eye. On emergence,
the larva begins to feed within the leaf, tunnelling forward as it proceeds. There are three
larval stages, all active feeders, and the width of the mine gets larger as the larva grows
(Figure 4) . When the larva is fully mature, it leaves the leaf by cutting a semi -circular exit
slit at the end of its mine. Usually it drops to the soil where pupation then takes place;
however, pupae are sometimes found attached to the external surface of leaves. When the
adults emerge, they return above ground to feed and lay eggs.
D ispersal and Detection
Liriomyza huidobrensis , L. sativae and L. trifolii are all regularly intercepted during routine
port -of -entry inspections in England and Wales carried out by the Plant Health and S eed
Inspectorate (PHSI) . These findings have been on a wide variety of plant s originating from
many different parts of the world.
Feeding punctures and leaf mines are usually the first and most obvious signs of the
presence of Liriomyza within a crop . Feeding punctures are rounded, about 0.2 mm in
diameter, and appear as white spe ckles on the upper surface of the leaf (Figure 3) . The
larvae feed mostly in the upper part of the leaf, mining through the green palisade tissue.
In L. huidobrensis , the mine can also undulate between the upper and lower surfaces of
the leaf. Mines are us ually off -white, with trails of frass (insect faeces) appearing as broken
black lines along the length of the mine. Repeated convolutions in the same area of leaf
tissue can eventually lead to dampened black and brown patches appearing. A mine will
remain intact and relatively unchanged over a period of weeks, even once the larva has
left the mine.
The mines tend to have a general corridor -type shape, though there is a greater or lesser
twisting of the mine according to species and other factors (Figures 3 and 4) . Although the
different quarantine species show certain characteristic tendencies in the appearance of
their mines, there is too much variation (particularly when comparing mines on different
host plants) for identification to be made with certainty on the basis of mine configuration
alone.
Chromatomyia syngenesiae and C. horticola are the two native polyphagous leaf miners
that are most likely to be found on crops under protective cultivation in the UK. Their mines
tend to appear cleaner than those of the Liriomyza species, and ar e often less convoluted.
Furthermore , these species pupate within the mine, and the extended -cylindrical pupa can
be found in situ at the end of the mine , usually visible on the underside of the leaf .
Adult Liriomyza flies are readily caught on yellow sticky traps placed adjacent to an
infested crop (Figure 5) .
Economic Impact
The damage caused by Liriomyza leafminers reduces the photosynthetic ability of the
plants, thus reducing the vigour and productivity of the pl ant. For ornamentals the damage
also reduces the aesthetic and retail value of the plants. Damage in severe infestations
can lead to total crop losses.
Advisory Information
Liriomyza huidobrensis , L. sativae and L. trifolii are all quarantine species a nd are
notifiable pests in the UK. Any suspicions of their presence must be reported to the
relevant authorities (see below) . Liriomyza bryoniae remains absent from the island of
Ireland, and as such remains a notifiable pest in both Northern Ireland and t he Republic of
Ireland.
Suspected outbreaks of quarantine Liriomyza species, or any other non -native plant pest ,
should be reported to the relevant authority:
For England and Wales , contact your local APHA Plant Health and Seeds Inspector or
the PHSI Headquarters , Sand Hutton, York. Tel: 01904 405138
Email: planthealth.info@apha.gsi.gov.uk
For Scotland , contact the Scottish Government’s Horticulture and Marketing Unit:
Email: hort.marketing@gov.scot
For Northern Ireland , c ontact the DARD Plant Health Inspection Branch:
Tel: 0300 200 7847 Email: planthealth@dardni.gov.uk
For additi onal information on UK Plant Health please see:
https://secure.fera.defra.gov.uk/phiw/riskRegister/
https://www.gov.uk/plant -he alth -controls
https://www.dardni.gov.uk/
Authors
Dom Collins (Fera) and Helen Anderson (Defra)
Date : November 2016
© Crown copyright 201 6
