Copy a link to this page Cite this record

Ragwort leafminer - Chromatomyia syngenesiae

By N A Martin (2017)

Show more

Click to collapse Classification Info





Chromatomyia syngenesiae Hardy, 1849

Click to collapse Common names Info

Ragwort leafminer, Chrysanthemum leafminer, Chyrsanthemum leaf miner, Cineraria Leafminer

Click to collapse Synonyms Info

Phytomyza albiceps Meigen

Phytomyza atricornis Meigen, 1838

Phytomyza syngenesiae (Hardy, 1849)

Click to collapse Biostatus and distribution Info

This adventive fly from Europe is found throughout New Zealand. It is a polyphagous leaf miner that is mainly found on herbaceous Compositae (daisy family). It occurs in crop, ornamental and adventive plants, as well as on native plants especially in the genus Senecio. If it was not controlled by natural enemies, it could put some rare native plants at risk of extinction.

Conservation status: Widespread. It occurs on native plants, but populations are controlled by many species of natural enemies.

Click to collapse Life stages and annual cycle Info

The fly breeds all year. Up to 15 complete generations in 12 months were confirmed by a New Zealand entomologist Jack Kelsey, who made detailed observations on the fly that were published in 1937. Populations are highest in spring and early summer, after which numbers are reduced by natural enemies, especially wasp parasitoids.

Adult fly

The flies are small, about 4 mm long, similar to the size of vinegar flies, Drosophila species, that are seen around rotting fruit. The body is grey-black with a pale head between the red compound eyes. The short antennae are black. It is a typical fly, having one pair of wings. The hind pair of wings is reduced to two small knobs, or halteres, which help the fly to balance during flight. The male has rounded black external genitalia at the end of the abdomen, while the female has a dark slender end containing an ovipositor. The ovipositor is used to make holes in host plant leaves into which eggs are laid. Females also feed on leaf sap from holes in leaves made with their ovipositor.

Eggs and larvae

Single eggs are inserted into the upper side or underside of leaves. Newly hatched larvae tunnel into leaves making mines that are visible on one side of the leaf, usually the upper side. The larvae feed on the internal cells of the leaf. They have a single black jaw which is moved from side-to-side, scraping the plant cells at the head of the mine. The plant cells are ingested and the dark green faeces excreted into the mine behind it, usually on one side of the mine. The larva moults, or changes skin, as it gets larger. There are three larval stages (instars). A fully grown larva is about 4 mm long.

The mine starts where the egg is laid and meanders through the leaf. The mine gradually widens and may change sides of the leaf. Often, just before pupation, the mine goes from the top of the leaf to the underside for a short distance. The mature larva pupates in the leaf.


The larva pupates inside its larval skin, which usually turns brown and hard. This structure is called a puparium. The puparium may be pale or dark brown. It has a pair of stigmata (organs for breathing) at each end of the body. The front, anterior, pair of stigmata are close together and project through the skin of the leaf mine. After a while, the eyes and bristles of the adult fly can be seen through the skin of the puparium.

Fly emergence

When ready to emerge, part of the head, just above the antennae, balloons out. This structure, the ptilinum, pushes the front of the pupa open. There is a line of weakness between the top and bottom halves of the first three-and-a-half segments that splits allowing the top and bottom to open up. This flap pushes up and tears the skin, epidermis, of the leaf. After the fly has crawled out, the ptilinum retracts into the head, the wings expand, and the body hardens. Over the next 12 hours the fly acquires its full body colour.

It is not known how the male and females of this species find each other for mating.

Click to collapse Recognition Info

These small grey black flies require expert knowledge for identification. The female fly is not distinguishable from the plantain leafminer, Phytomyza plantaginis Robineau-Desvoidy, 1851. However, the species can be detected and identified by its leaf mines and by the fact that it pupates in the mine.

In Senecio species another leaf miner may be present, a moth, Stigmella ogygia (Meyrick, 1889) (Lepidoptera: Nepticulidae). The mines formed by the caterpillar are distinct. Initially they are very narrow and serpentine. As they get wider, a central black line of frass, excreta, can be seen. Also the caterpillar leaves the mine to spin a cocoon in which they pupate.

See Host Plants and Other Images for more photographs of mines in host plants.

Click to collapse Natural enemies Info


There are no reports of predators of the flies, but it is likely that they are preyed upon by birds, spiders and predatory insects. Some female wasp parasitoids feed on leaf miner fly larvae as well as parasitising other fly larvae. Some birds may be able to recognise the presence of puparia and feed on them.


Many species of parasitoid wasps have been reared from larvae and puparia of ragwort leafminers in New Zealand and other countries. Some parasitoids only live on the ragwort leafminer, whereas others live on more than one species of leaf miner, including non-fly leaf miners. In late spring and summer, a high proportion of ragwort leafminer larvae and pupae are killed by parasitoids.

The ragwort leafminer parasitoid, Dacnusa areolaris (Nees, 1812) (Hymenoptera: Braconidae), only lives in the ragwort leafminer. The female wasp lays an egg in a fly larva. The fly larva is not killed until it has pupated and the wasp pupates in the fly puparium. Another wasp parasitoid that lives in the fly larva and emerges from the fly puparium is Opius cinerariae Fisher, 1963 (Hymenoptera: Braconidae). Hemiptarsenus varicornis (Girault, 1913) (Hymenoptera: Eulophidae) is a parasitoid of fly larvae and pupae, while Chrysocharis pubicornis (Zetterstedt, 1838) (Hymenoptera: Eulophidae) is a parasitoid of leaf miner fly pupae. Other wasp parasitoids kill small fly larvae in the mines and feed from the outside of the fly. Those commonly found parasitising ragwort leafminers are Diglyphus isaea (Walker, 1838) and Chrysonotomyia species (Eulophidae). Proacrias sp. (Eulophidae) is also common and kills small fly larvae. Several other unidentified species of parasitoids have been reared from ragwort leafminers.

Table: Natural enemies of Ragwort leafminer, Chromatomyia syngenesiae (Diptera: Agromyzidae), from Plant-SyNZ database (15 April 2017). The reliability index shows the quality of evidence for the host association (0-10, 10=high quality).
Scientific NameCommon NameClassificationEnemy TypeReliability IndexBiostatus
Chrysocharis pubicornis (Zetterstedt, 1838) (Wasp)Hymenoptera: Eulophidaeparasitoid10adventive
Chrysonotomyia sp. 'Agromyzidae' of Berry 2000 (Wasp)Hymenoptera: Eulophidaeparasitoid7endemic
Dacnusa areolaris (Nees, 1812)Ragwort leaf miner parasite (Wasp)Hymenoptera: Braconidaeparasitoid10adventive
Diglyphus isaea (Walker, 1838)Parasitic eulophid wasp (Wasp)Hymenoptera: Eulophidaeparasitoid10adventive
Encyrtidae sp. 2 of Berry 1998 (Wasp)Hymenoptera: Encyrtidaeparasitoid6unknown
Hemiptarsenus varicornis (Girault, 1913) (Wasp)Hymenoptera: Eulophidaeparasitoid10adventive
Opius cinerariae Fisher, 1963 (Wasp)Hymenoptera: Braconidaeparasitoid9adventive
Proacrias n.sp. (J. Berry 2001) (Wasp)Hymenoptera: Eulophidaeparasitoid8endemic

Click to collapse Host plants Info

Ragwort leafminer mainly forms leaf mines in Compositae (daisy family), but sometimes may be found in Leguminosae (pea family), Labiatae (mint family) Papaveraceae (poppy family) and others. Host plants include cultivated flowers and vegetables, adventive plants and native species. Native plants affected include Sonchus kirki, Senecio species and New Zealand celery, Apium prostatum.

The adult female fly makes small punctures in young leaves for egg laying and for feeding. The larva burrows through the leaf, making mines that are visible on one side of the leaf, usually the upper side. The mine meanders through the leaf gradually widening. A heavy infestation can remove all green leaf tissue turning the leaf white. A severe attack on a seedling or young plant could kill it.

More examples of damage to plants are under Other Images.

Table: Host plants of the Ragwort leafminer, Chromatomyia syngenesiae (Diptera: Agromyzidae) from Plant-SyNZ database (15 April 2017). The reliability score shows the quality of evidence for the host association (1-10, 10=high).
Common Name(s)Scientific NameFamilyReliability IndexBiostatus
New Zealand celery, Sea celery, Shore celery, Tūtae kōauApium prostratum Labill. ex Vent.Umbelliferae10indigenous, non-endemic
Common burdockArctium minus (Hill) Bernh.Compositae10naturalised
Capeweed, Cape weedArctotheca calendula (L.) LevynsCompositae9naturalised
Hedge artemisia, WormwoodArtemisia arborescens L.Compositae10naturalised
Estragon, TarragonArtemisia dracunculus L.Compositae10naturalised
Michaelmas daisyAster sp. 'garden cultivar' of Martin 2001Compositae8cultivated
Winged thistleCarduus tenuiflorus CurtisCompositae9naturalised
Mountain bluet, Perennial cornflowerCentaurea montana L.Compositae9naturalised
Black knapweed, Lesser knapweedCentaurea nigra L.Compositae9naturalised
Boar thistle, Bull thistle, Scotch thistle, Spear thistle, Pūngitangita, PūnitanitaCirsium vulgare (Savi) Ten.Compositae10naturalised
HawksbeardCrepis sp.Compositae7naturalised
Apple cucumber, Cucumber, Khira, Long green cucumberCucumis sativus L.Cucurbitaceae9cultivated
Tree dahliaDahlia imperialis Roezel ex OrtgiesCompositae10naturalised
DahliaDahlia sp.Compositae7unknown
German ivyDelairea odorata Lem.Compositae10naturalised
 Dolichoglottis lyallii (Hook.f.) B.Nord.Compositae5endemic
Broad-leaved fleabane, Tall fleabane, Hāka, Kaingarua, Porerarua, PouhawaikiErigeron sumatrensis Retz.Compositae9naturalised
Galinsoga, Potato weedGalinsoga parviflora Cav.Compositae8naturalised
African daisy, Barberton daisyGerbera jamesonii AdlamCompositae9naturalised
Common sunflower, SunflowerHelianthus annuus L.Compositae9naturalised
Ox tongue, OxtongueHelminthotheca echioides (L.) HolubCompositae10indigenous, non-endemic
Cats ear, Flatweed, Spotted cat's-earHypochaeris radicata LCompositae10naturalised
Ragwort, Saint James' wort, Tansy ragwortJacobaea vulgaris Gaertn.Compositae10naturalised
Candle plantKleinia articulata (Linné fil.) Haworth 1812Compositae10cultivated
LettuceLactuca sativa L.Compositae10naturalised
Red dead nettleLamium purpureum L.Labiatae7naturalised
NipplewortLapsana communis L.Compositae10naturalised
Oxeye daisy, Ox-eye daisyLeucanthemum vulgare Lam.Compositae10naturalised
CatnipNepeta cataria L.Labiatae10naturalised
Corn poppy, Field poppy, Flanders poppyPapaver rhoeas L.Papaveraceae10naturalised
CinerariaPericallis ×hybrida (Scheidw.) B.Nord.Compositae10naturalised
Butterbur, Winter heliotropePetasites fragrans (Vill.) C.Presl.Compositae9naturalised
HawkweedPicris burbidgeae S.HolzapfelCompositae9indigenous, non-endemic
Field pea, Garden pea, Snow peaPisum sativum L.Leguminosae10naturalised
Australian fireweedSenecio bipinnatisectus BelcherCompositae10naturalised
FireweedSenecio esleri C.J.WebbCompositae8naturalised
Fireweed, PukateaSenecio glomeratus Poir.Compositae10indigenous, non-endemic
FireweedSenecio hispidulus A.Rich.Compositae10indigenous, non-endemic
Fireweed, Shore groundsel, Variable groundselSenecio lautus G.Forst. ex Willd.Compositae10indigenous, non-endemic
Australian burnweed, Australian fireweed, FireweedSenecio minimus Poir.Compositae9indigenous, non-endemic
Cotton fireweed, White fireweed, Pahohoraka, PekapekaSenecio quadridentatus Labill.Compositae8indigenous, non-endemic
 Senecio radiolatus F.Muell. subsp. antipodus (Kirk) C.J.WebbCompositae10endemic
Pūhāureroa, PūwhāureroaSenecio rufiglandulosus ColensoCompositae9endemic
Gravel groundselSenecio skirrhodon DC.Compositae10naturalised
Common groundsel, GroundselSenecio vulgaris L.Compositae10naturalised
Perennial sow thistleSonchus arvensis L.Compositae8naturalised
Prickly sow thistle, Rough sow thistle, Kautara, Pūhā tiotio, Puhapuha, Raurōroa, Taweke, Tiotio, WekewekeSonchus asper (L.) HillCompositae10naturalised
New Zealand sow thistle, Shore puha, Kautara, Pūhā, Pūhā tiotio, Puhapuha, Raurōroa, Taweke, Tiotio, WekewekeSonchus kirkii HamlinCompositae9endemic
Common sow thistle, Sow thistle, Milky thistle, Pororua, Pūhā, Pūwhā, RaurikiSonchus oleraceus L.Compositae10naturalised
French marigoldTagetes patula L.Compositae9naturalised
FeverfewTanacetum parthenium (L.) Sch.Bip.Compositae7naturalised
Dandelion, Tawao, Tohetaka, Tohetake, ToheteaTaraxacum officionale F.H.Wigg.Compositae10naturalised
Blowballs, DandelionTaraxacum sp.Compositae7unknown
White cloverTrifolium repens L.Leguminosae10naturalised

Click to collapse Control Info

Leaf mines made by the ragwort leafminer, Chromatomyia syngenesiae, may be found on some garden plants, such as chrysanthemums and cinerarias. Normally little damage is caused because populations of the fly are kept low by wasp parasitoids.

If the leafminer is a problem in commercial crops and pesticides are required, it is best to choose products that cause least harm to natural enemies such as the wasp parasitoids.

Click to collapse Additional information Info

Risk to native plants

Ragwort leafminer poses a risk to rare native plants in the genus Senecio. This is because it is a polyphagous herbivore that has many species of host plants, some of which are very common and can support high numbers of the leaf miner. This means that if alternative host plants are in areas with rare native Senecio species, the leaf miner populations can increase on the other host plants and then infest the rare plant. High numbers of larvae in leaves can remove all the green tissue. If this happens to all leaves in a seedling or small plant, the plant could die without producing viable seeds. Fortunately, ragwort leafminer is susceptible to many parasitoids that appear to reduce populations after a spring peak, which in turn reduces the risk to rare plants.

A potential biological control agent for ragwort

In the 1930s, DSIR entomologists were impressed by the number of leaf mines made in ragwort by the ragwort leafminer. Ragwort, Jacobaea vulgaris Gaertn. (Compositae), was then and still is a serious pest of cattle-grazed pastures. One entomologist, Jack Kelsey, investigated the biology of the leaf miner and one of its wasp parasitoids (see Information Sources, Kelsey 1937). The parasitoid complex that includes adventive and indigenous species prevents high populations of the leafminer developing and reduces its potential as a biological control agent.

Leaf mining flies in the family Agromyzidae are potential biological control agents of other weeds, but the presence of a complex of parasitoids of these flies in New Zealand limits the potential of these flies as biological control agents.

Research Project: Possible strategies for avoiding predators

Two features of the ragwort leafminer behaviour may be linked to reducing the chance of puparia being eaten by predators such as birds.

First, the puparia may be pale, light tan, or dark brown in colour. The visibility of these two colour forms appears to vary with the kind of leaf in which the fly is living. However, the susceptibility to predation by birds of the two colour variants in different host plants has not been investigated.

Second, on some plants, such as sowthistle/puha (Sonchus species), the leaf mines are visible on the upper side of the leaf. Just before pupation the mine often moves to the underside of the leaf for a short distance. Is this so that birds do not learn to look for the puparium at the end of a white mine? This behaviour of changing leaf sides is not consistent. Is it more or less variable here compared with Europe?

Click to collapse Information sources Info

Kelsey JM 1937. The ragwort leaf-miner (Phytomyza atricornis Mg.) and its parasite (Dacnusa areolaris Nees.). The New Zealand Journal of Science and Technology 18: 762-767.

Spencer KA 1976. The Agromyzidae of New Zealand (Insecta: Diptera). Journal of the Royal Society of New Zealand 6(2): 153-211.

Click to collapse Acknowledgements Info

The New Zealand Institute for Plant & Food Research Limited (Plant & Food Research) for permission to use photographs.

Click to collapse Other images Info

Click to go back to the top of the page