Ragwort leafminer - Chromatomyia syngenesiae

By N A Martin (2017)

Caption:

Classification

Phylum

Arthropoda

Class

Insecta

Order

Diptera

Family

Agromyzidae

Scientific name

Chromatomyia syngenesiae Hardy, 1849

Common names

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

Synonyms

Phytomyza albiceps Meigen

Phytomyza atricornis Meigen, 1838

Phytomyza syngenesiae (Hardy, 1849)

Biostatus and distribution

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.

Life stages and annual cycle

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.

Pupa

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.

Top view of an adult female ragwort leafminer, Chromatomyia syngenesiae (Diptera: Agromyzidae). Creator: Tim Holmes. © Plant & Food Research. [Image: 2HKK]

Mine on underside of leaf of common sow thistle, Sonchus oleraceus (Compositae), with puparium of ragwort leafminer, Chromatomyia syngenesiae (Diptera: Agromyzidae): note the stigma (breathing tubes) sticking through the epidermis of the leaf. Creator: Tim Holmes. © Plant & Food Research. [Image: 2HJX]

Underside of an adult female ragwort leafminer, Chromatomyia syngenesiae (Diptera: Agromyzidae). Creator: Tim Holmes. © Plant & Food Research. [Image: 2HKF]

Side view of an adult female ragwort leafminer, Chromatomyia syngenesiae (Diptera: Agromyzidae). Creator: Tim Holmes. © Plant & Food Research. [Image: 2HKG]

Side view of an adult female ragwort leafminer, Chromatomyia syngenesiae (Diptera: Agromyzidae). Creator: Tim Holmes. © Plant & Food Research. [Image: 2HKH]

Underside of an adult male ragwort leafminer, Chromatomyia syngenesiae (Diptera: Agromyzidae). Creator: Tim Holmes. © Plant & Food Research. [Image: 2HKQ]

Three larvae of ragwort leafminer, Chromatomyia syngenesiae (Diptera: Agromyzidae) making leaf mines on common sow thistle, Sonchus oleraceus (Compositae). Note the black mandible and supporting skeleton in the larva on the right. Creator: Tim Holmes. © Plant & Food Research. [Image: 2HJZ]

Larva of ragwort leafminer, Chromatomyia syngenesiae (Diptera: Agromyzidae), partly dissected from a mine on common sow thistle, Sonchus oleraceus (Compositae). Note the black mandible and supporting skeleton. Creator: Tim Holmes. © Plant & Food Research. [Image: 2HK3]

Larva of ragwort leafminer, Chromatomyia syngenesiae (Diptera: Agromyzidae), dissected from a mine on common sow thistle, Sonchus oleraceus (Compositae). The white arrow points to the black mandible and supporting skeleton; the black arrow points to one of the two black posterior stigmata with the openings of the trachea, air ducts. Creator: Tim Holmes. © Plant & Food Research. [Image: 2HK4]

Pupa of ragwort leafminer, Chromatomyia syngenesiae (Diptera: Agromyzidae), in a mine on common sow thistle, Sonchus oleraceus (Compositae). The black arrow points to the larval mandibular skeleton which has both arms spread out. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2HKN]

Mine on upper side of leaf of common sow thistle, Sonchus oleraceus (Compositae), made by larvae of ragwort leafminer, Chromatomyia syngenesiae (Diptera: Agromyzidae): note the dark oval shadow of a puparium in a mine on the underside of the leaf. Creator: Tim Holmes. © Plant & Food Research. [Image: 2HJW]

Mine on underside of leaf of common sow thistle, Sonchus oleraceus (Compositae), made by larvae of ragwort leafminer, Chromatomyia syngenesiae (Diptera: Agromyzidae): note the dark brown puparium in the mine on the underside of the leaf. Creator: Tim Holmes. © Plant & Food Research. [Image: 2HJY]

Puparium of ragwort leafminer, Chromatomyia syngenesiae (Diptera: Agromyzidae), in a mine on common sow thistle, Sonchus oleraceus (Compositae): note the two anterior stigmata protruding through the epidermis (skin of the leaf), the stigmata connect with the trachea, air ducts. Creator: Tim Holmes. © Plant & Food Research. [Image: 2HLB]

Puparium of ragwort leafminer, Chromatomyia syngenesiae (Diptera: Agromyzidae) in a mine on common sow thistle, Sonchus oleraceus (Compositae), after the adult fly has emerged. The black arrow points to the mandibular skeleton. Creator: Tim Holmes. © Plant & Food Research. [Image: 2HLA]

Puparium of ragwort leafminer, Chromatomyia syngenesiae (Diptera: Agromyzidae), after the adult fly has emerged. The black arrow points to the hole in the epidermis (skin) of the leaf and the split in the front of the puparium. Creator: Tim Holmes. © Plant & Food Research. [Image: 2HLC]

Recognition

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.

Top view of an adult female ragwort leafminer, Chromatomyia syngenesiae (Diptera: Agromyzidae). Creator: Tim Holmes. © Plant & Food Research. [Image: 2HKE]

Leaf mines in ragwort, Jacobaea vulgaris (Compositae), made by larvae of ragwort leafminer, Chromatomyia syngenesiae (Diptera: Agromyzidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2HJQ]

Mines on underside of a dandelion, Taraxacum officionale (Compositae), leaf made by larvae of ragwort leafminer, Chromatomyia syngenesiae (Diptera: Agromyzidae). Two brown puparia are present. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2HKV]

Mines on underside of leaf of gerbera, Gerbera jamesonii (Compositae), made by larvae of ragwort leafminer, Chromatomyia syngenesiae (Diptera: Agromyzidae). Brown puparia are present. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2HKC]

Leaf mine in fireweed, Senecio minimus (Compositae), made by a caterpillar of Stigmella ogygia (Meyrick, 1889) (Lepidoptera: Nepticulidae): note the narrow serpentine start to the mine and the central black line of frass, excreta. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2HJC]

Natural enemies

Predators

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.

Parasitoids

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.

Top side of male (left) and female ragwort leafminer parasitoids, Dacnusa areolaris (Nees, 1812) (Hymenoptera: Braconidae). The wasp emerges from the puparium of ragwort leafminer, Chromatomyia syngenesiae (Diptera: Agromyzidae). Creator: Tim Holmes. © Plant & Food Research. [Image: 2HJE]

Underside of male (left) and female ragwort leafminer parasitoids, Dacnusa areolaris (Nees, 1812) (Hymenoptera: Braconidae). The wasp emerges from the puparium of ragwort leafminer, Chromatomyia syngenesiae (Diptera: Agromyzidae). Creator: Tim Holmes. © Plant & Food Research. [Image: 2HJF]

Front of a ragwort leafminer parasitoid, Dacnusa areolaris (Nees, 1812) (Hymenoptera: Braconidae). The wasp emerges from the puparium of ragwort leafminer, Chromatomyia syngenesiae (Diptera: Agromyzidae). Creator: Tim Holmes. © Plant & Food Research. [Image: 2HJD]

Dead larvae of ragwort leafminer, Chromatomyia syngenesiae (Diptera: Agromyzidae), with an internal parasitoid larva. Note how a constriction passes down the dark parasitoid gut. Creator: Tim Holmes. © Plant & Food Research. [Image: 2HLD]

Parasitoid pupa of ragwort leafminer, Chromatomyia syngenesiae (Diptera: Agromyzidae), in leaf mine: note the black faecal columns on either side of the pupa. Creator: Tim Holmes. © Plant & Food Research. [Image: 2HLJ]

Parasitoid pupa of ragwort leafminer, Chromatomyia syngenesiae (Diptera: Agromyzidae), exposed in leaf mine: note the white cord (at tip of black arrow) with which the pupa is attached to the leaf. Creator: Tim Holmes. © Plant & Food Research. [Image: 2HLG]

Round exit hole of adult parasitoid of ragwort leafminer, Chromatomyia syngenesiae (Diptera: Agromyzidae), in leaf mine. The parasitoid pupal skin is in the mine to the right of the arrow. Creator: Tim Holmes. © Plant & Food Research. [Image: 2HLM]

Adult parasitoid of ragwort leafminer, Chromatomyia syngenesiae (Diptera: Agromyzidae), top view. Creator: Tim Holmes. © Plant & Food Research. [Image: 2HLL]

Adult parasitoid of ragwort leafminer, Chromatomyia syngenesiae (Diptera: Agromyzidae), underside. Creator: Tim Holmes. © Plant & Food Research. [Image: 2HLK]

Puparium of ragwort leafminer, Chromatomyia syngenesiae (Diptera: Agromyzidae), with exit hole made by an adult parasitoid. Creator: Tim Holmes. © Plant & Food Research. [Image: 2HLP]

Adult parasitoid of ragwort leafminer, Chromatomyia syngenesiae (Diptera: Agromyzidae). The parasitoid larva had pupated in the fly puparium. Creator: Tim Holmes. © Plant & Food Research. [Image: 2HLQ]

Two ectoparasitic larvae (arrows) of Diglyphus isaea(Walker, 1838) (Hymenoptera: Eulophidae) feeding on larva of a leafminer, Liriomyza sp. (Diptera: Agromyzidae). Creator: Tim Holmes. © Plant & Food Research. [Image: 154P]

Adult Diglyphus isaea (Walker, 1838) (Hymenoptera: Eulophidae) after chewing an exit hole from a leaf mine of Liriomyza sp. (Diptera: Agromyzidae). Creator: Tim Holmes. © Plant & Food Research. [Image: 1551]

Top view of adult Diglyphus isaea (Walker, 1838) (Hymenoptera: Eulophidae), an ectoparasite of larvae of leafminer flies (Diptera: Agromyzidae). Creator: Tim Holmes. © Plant & Food Research. [Image: 1555]

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 Name	Common Name	Classification	Enemy Type	Reliability Index	Biostatus
Chrysocharis pubicornis (Zetterstedt, 1838)	(Wasp)	Hymenoptera: Eulophidae	parasitoid	10	adventive
Chrysonotomyia sp. 'Agromyzidae' of Berry 2000	(Wasp)	Hymenoptera: Eulophidae	parasitoid	7	endemic
Dacnusa areolaris (Nees, 1812)	Ragwort leaf miner parasite (Wasp)	Hymenoptera: Braconidae	parasitoid	10	adventive
Diglyphus isaea (Walker, 1838)	Parasitic eulophid wasp (Wasp)	Hymenoptera: Eulophidae	parasitoid	10	adventive
Encyrtidae sp. 2 of Berry 1998	(Wasp)	Hymenoptera: Encyrtidae	parasitoid	6	unknown
Hemiptarsenus varicornis (Girault, 1913)	(Wasp)	Hymenoptera: Eulophidae	parasitoid	10	adventive
Opius cinerariae Fisher, 1963	(Wasp)	Hymenoptera: Braconidae	parasitoid	9	adventive
Proacrias n.sp. (J. Berry 2001)	(Wasp)	Hymenoptera: Eulophidae	parasitoid	8	endemic

Host plants

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.

Leaf mines in cineraria, Pericallis x hybrida (Compositae), made by larvae of ragwort leafminer, Chromatomyia syngenesiae (Diptera: Agromyzidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2HK7]

Leaf mines in common sowthistle, Sonchus oleraceus (Compositae), made by larvae of ragwort leafminer, Chromatomyia syngenesiae (Diptera: Agromyzidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2HKY]

Leaf mines in tree dahlia, Dahlia imperialis (Compositae), made by larvae of ragwort leafminer, Chromatomyia syngenesiae (Diptera: Agromyzidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2HKU]

Leaf mines in sunflower, Helianthus annuus (Compositae), made by larvae of ragwort leafminer, Chromatomyia syngenesiae (Diptera: Agromyzidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2HL7]

Leaf mines in two leaves of fireweed, Senecio glomeratus (Compositae), made by larvae of ragwort leafminer, Chromatomyia syngenesiae (Diptera: Agromyzidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2HKM]

Leaf mines in shore groundsel, Senecio lautus (Compositae), made by larvae of ragwort leafminer, Chromatomyia syngenesiae (Diptera: Agromyzidae). Creator: Nicholas A. Martin. © Nicholas A. Martin. [Image: 2HL1]

Leaf mines in fireweed, Senecio minimus (Compositae), made by larvae of ragwort leafminer, Chromatomyia syngenesiae (Diptera: Agromyzidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2HJM]

White leaf mines in puwhaureroa, Senecio rufiglandulosus (Compositae), made by larvae of ragwort leafminer, Chromatomyia syngenesiae (Diptera: Agromyzidae). The thin brown mines were made by a caterpillar, Stigmella ogygia (Meyrick, 1889) (Lepidoptera: Nepticulidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2HJI]

Leaf mines in cotton fireweed, Senecio quadridentatus (Compositae), made by larvae of ragwort leafminer, Chromatomyia syngenesiae (Diptera: Agromyzidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2HJN]

High density of mines turning white leaves of Sonchus sp. (Compositae); mines made by larvae of ragwort leafminer, Chromatomyia syngenesiae (Diptera: Agromyzidae). Creator: Nicholas A. Martin. © Nicholas A. Martin. [Image: 2HL4]

Leaf mines in fireweed, Senecio hispidulus (Compositae), made by larvae of ragwort leafminer, Chromatomyia syngenesiae (Diptera: Agromyzidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2HKP]

Leaf mine in New Zealand celery, Apium prostratum (Umbelliferae), made by larvae of ragwort leafminer, Chromatomyia syngenesiae (Diptera: Agromyzidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2HKS]

Leaf mines in Cucumber, Cucumis sativus (Cucurbitaceae), made by larvae of ragwort leafminer, Chromatomyia syngenesiae (Diptera: Agromyzidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2HJS]

Leaf mines in Cucumber, Cucumis sativus (Cucurbitaceae), made by larvae of ragwort leafminer, Chromatomyia syngenesiae (Diptera: Agromyzidae). The black arrow points to a puparium in a mine. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2HJT]

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 Name	Family	Reliability Index	Biostatus
New Zealand celery, Sea celery, Shore celery, Tūtae kōau	Apium prostratum Labill. ex Vent.	Umbelliferae	10	indigenous, non-endemic
Common burdock	Arctium minus (Hill) Bernh.	Compositae	10	naturalised
Capeweed, Cape weed	Arctotheca calendula (L.) Levyns	Compositae	9	naturalised
Hedge artemisia, Wormwood	Artemisia arborescens L.	Compositae	10	naturalised
Estragon, Tarragon	Artemisia dracunculus L.	Compositae	10	naturalised
Michaelmas daisy	Aster sp. 'garden cultivar' of Martin 2001	Compositae	8	cultivated
Winged thistle	Carduus tenuiflorus Curtis	Compositae	9	naturalised
Mountain bluet, Perennial cornflower	Centaurea montana L.	Compositae	9	naturalised
Black knapweed, Lesser knapweed	Centaurea nigra L.	Compositae	9	naturalised
Boar thistle, Bull thistle, Scotch thistle, Spear thistle, Pūngitangita, Pūnitanita	Cirsium vulgare (Savi) Ten.	Compositae	10	naturalised
Hawksbeard	Crepis sp.	Compositae	7	naturalised
Apple cucumber, Cucumber, Khira, Long green cucumber	Cucumis sativus L.	Cucurbitaceae	9	cultivated
Tree dahlia	Dahlia imperialis Roezel ex Ortgies	Compositae	10	naturalised
Dahlia	Dahlia sp.	Compositae	7	unknown
German ivy	Delairea odorata Lem.	Compositae	10	naturalised
	Dolichoglottis lyallii (Hook.f.) B.Nord.	Compositae	5	endemic
Broad-leaved fleabane, Tall fleabane, Hāka, Kaingarua, Porerarua, Pouhawaiki	Erigeron sumatrensis Retz.	Compositae	9	naturalised
Galinsoga, Potato weed	Galinsoga parviflora Cav.	Compositae	8	naturalised
African daisy, Barberton daisy	Gerbera jamesonii Adlam	Compositae	9	naturalised
Common sunflower, Sunflower	Helianthus annuus L.	Compositae	9	naturalised
Ox tongue, Oxtongue	Helminthotheca echioides (L.) Holub	Compositae	10	indigenous, non-endemic
Cats ear, Flatweed, Spotted cat's-ear	Hypochaeris radicata L	Compositae	10	naturalised
Ragwort, Saint James' wort, Tansy ragwort	Jacobaea vulgaris Gaertn.	Compositae	10	naturalised
Candle plant	Kleinia articulata (Linné fil.) Haworth 1812	Compositae	10	cultivated
Lettuce	Lactuca sativa L.	Compositae	10	naturalised
Red dead nettle	Lamium purpureum L.	Labiatae	7	naturalised
Nipplewort	Lapsana communis L.	Compositae	10	naturalised
Oxeye daisy, Ox-eye daisy	Leucanthemum vulgare Lam.	Compositae	10	naturalised
Catnip	Nepeta cataria L.	Labiatae	10	naturalised
Corn poppy, Field poppy, Flanders poppy	Papaver rhoeas L.	Papaveraceae	10	naturalised
Cineraria	Pericallis ×hybrida (Scheidw.) B.Nord.	Compositae	10	naturalised
Butterbur, Winter heliotrope	Petasites fragrans (Vill.) C.Presl.	Compositae	9	naturalised
Hawkweed	Picris burbidgeae S.Holzapfel	Compositae	9	indigenous, non-endemic
Field pea, Garden pea, Snow pea	Pisum sativum L.	Leguminosae	10	naturalised
Australian fireweed	Senecio bipinnatisectus Belcher	Compositae	10	naturalised
Fireweed	Senecio esleri C.J.Webb	Compositae	8	naturalised
Fireweed, Pukatea	Senecio glomeratus Poir.	Compositae	10	indigenous, non-endemic
Fireweed	Senecio hispidulus A.Rich.	Compositae	10	indigenous, non-endemic
Fireweed, Shore groundsel, Variable groundsel	Senecio lautus G.Forst. ex Willd.	Compositae	10	indigenous, non-endemic
Australian burnweed, Australian fireweed, Fireweed	Senecio minimus Poir.	Compositae	9	indigenous, non-endemic
Cotton fireweed, White fireweed, Pahohoraka, Pekapeka	Senecio quadridentatus Labill.	Compositae	8	indigenous, non-endemic
	Senecio radiolatus F.Muell. subsp. antipodus (Kirk) C.J.Webb	Compositae	10	endemic
Pūhāureroa, Pūwhāureroa	Senecio rufiglandulosus Colenso	Compositae	9	endemic
Gravel groundsel	Senecio skirrhodon DC.	Compositae	10	naturalised
Common groundsel, Groundsel	Senecio vulgaris L.	Compositae	10	naturalised
Perennial sow thistle	Sonchus arvensis L.	Compositae	8	naturalised
Prickly sow thistle, Rough sow thistle, Kautara, Pūhā tiotio, Puhapuha, Raurōroa, Taweke, Tiotio, Wekeweke	Sonchus asper (L.) Hill	Compositae	10	naturalised
New Zealand sow thistle, Shore puha, Kautara, Pūhā, Pūhā tiotio, Puhapuha, Raurōroa, Taweke, Tiotio, Wekeweke	Sonchus kirkii Hamlin	Compositae	9	endemic
Common sow thistle, Sow thistle, Milky thistle, Pororua, Pūhā, Pūwhā, Rauriki	Sonchus oleraceus L.	Compositae	10	naturalised
French marigold	Tagetes patula L.	Compositae	9	naturalised
Feverfew	Tanacetum parthenium (L.) Sch.Bip.	Compositae	7	naturalised
Dandelion, Tawao, Tohetaka, Tohetake, Tohetea	Taraxacum officionale F.H.Wigg.	Compositae	10	naturalised
Blowballs, Dandelion	Taraxacum sp.	Compositae	7	unknown
White clover	Trifolium repens L.	Leguminosae	10	naturalised

Control

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.

Additional information

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?

Upper (top) and underside (bottom of leaf of common sowthistle, Sonchus oleraceus (Compositae), with leaf mine made by larvae of ragwort leafminer, Chromatomyia syngenesiae (Diptera: Agromyzidae). The arrows show where the mine has changed from the upper side of the leaf to the underside just before pupation on the underside. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2HKX]

Information sources

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.

Acknowledgements

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

Other images

Underside of an adult female ragwort leafminer, Chromatomyia syngenesiae (Diptera: Agromyzidae). Creator: Tim Holmes. © Plant & Food Research. [Image: 2HKJ]

Underside of an adult male ragwort leafminer, Chromatomyia syngenesiae (Diptera: Agromyzidae). Creator: Tim Holmes. © Plant & Food Research. [Image: 2HL6]

Larva of ragwort leafminer, Chromatomyia syngenesiae (Diptera: Agromyzidae) dissected from a mine in common sow thistle, Sonchus oleraceus (Compositae). Creator: Tim Holmes. © Plant & Food Research. [Image: 2HK5]

Larva of ragwort leafminer, Chromatomyia syngenesiae (Diptera: Agromyzidae), making a mine in common sow thistle, Sonchus oleraceus (Compositae). Creator: Tim Holmes. © Plant & Food Research. [Image: 2HK0]

Puparium of ragwort leafminer, Chromatomyia syngenesiae (Diptera: Agromyzidae), dissected from a mine in common sow thistle, Sonchus oleraceus (Compositae). Creator: Tim Holmes. © Plant & Food Research. [Image: 2HK2]

Dead larvae of ragwort leafminer, Chromatomyia syngenesiae (Diptera: Agromyzidae), with an internal parasitoid larva: note the dark parasitoid gut. Creator: Tim Holmes. © Plant & Food Research. [Image: 2HLE]

Parasitoid pupa of ragwort leafminer, Chromatomyia syngenesiae (Diptera: Agromyzidae), exposed in leaf mine: note the white cord with which the pupa is attached to the leaf. Creator: Tim Holmes. © Plant & Food Research. [Image: 2HLH]

Round exit hole made by adult parasitoid of ragwort leafminer, Chromatomyia syngenesiae (Diptera: Agromyzidae), in leaf mine; parasitoid pupal skin is in the mine to the right of the hole. Creator: Tim Holmes. © Plant & Food Research. [Image: 2HLN]

Leaf mines in potato weed, Galinsoga parviflora (Compositae), made by larvae of ragwort leafminer, Chromatomyia syngenesiae (Diptera: Agromyzidae). Creator: Nicholas A. Martin. © Nicholas A. Martin. [Image: 2HL0]

Leaf mines in fireweed, Senecio glomeratus (Compositae), made by larvae of ragwort leafminer, Chromatomyia syngenesiae (Diptera: Agromyzidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2HKZ]

Leaf mines in a dandelion, Taraxacum officionale (Compositae), made by larvae of ragwort leafminer, Chromatomyia syngenesiae (Diptera: Agromyzidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2HKW]

Mines in leaves of Michaelmas daisy, Aster sp. 'hairy garden cultivar' (Compositae), made by larvae of ragwort leafminer, Chromatomyia syngenesiae (Diptera: Agromyzidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2HKD]

Mines in leaves of Michaelmas daisy, Aster sp. 'garden cultivar' (Compositae), made by larvae of ragwort leafminer, Chromatomyia syngenesiae (Diptera: Agromyzidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2HJJ]

Mines in upper side of leaf of gerbera, Gerbera jamesonii (Compositae), made by larvae of ragwort leafminer, Chromatomyia syngenesiae (Diptera: Agromyzidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2HK9]

Mines in underside of leaf of gerbera, Gerbera jamesonii (Compositae), made by larvae of ragwort leafminer, Chromatomyia syngenesiae (Diptera: Agromyzidae): note the pale brown puparia. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2HKB]

Mines in underside (left) and upper side (right) of leaves of cineraria, Pericallis x hybrida (Compositae), made by larvae of ragwort leafminer, Chromatomyia syngenesiae (Diptera: Agromyzidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2HK8]

Mines in upper side of leaf of capeweed, Arctotheca calendula (Compositae), made by larvae of ragwort leafminer, Chromatomyia syngenesiae (Diptera: Agromyzidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2HK6]

Mines in upper side of leaves of candle plant, Kleinia articulata (Compositae), made by larvae of ragwort leafminer, Chromatomyia syngenesiae (Diptera: Agromyzidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2HJU]

Mines in upper side (left) and underside (right) of leaves of candle plant, Kleinia articulata (Compositae), made by larvae of ragwort leafminer, Chromatomyia syngenesiae (Diptera: Agromyzidae): note the brown puparium on the underside of leaf. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2HJV]

Mines in upper side of leaf of cats ear, Hypochaeris radicata (Compositae), made by larvae of ragwort leafminer, Chromatomyia syngenesiae (Diptera: Agromyzidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2HJR]

Mines in upper side of leaf of gravel groundsel, Senecio skirrhodon (Compositae), made by larvae of ragwort leafminer, Chromatomyia syngenesiae (Diptera: Agromyzidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2HJP]

Mines in upper side of leaf of field poppy, Papaver rhoeas (Papaveraceae), made by larvae of ragwort leafminer, Chromatomyia syngenesiae (Diptera: Agromyzidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2HJL]

Mines in upper side of leaf of common groundsel, Senecio vulgaris (Compositae), made by larvae of ragwort leafminer, Chromatomyia syngenesiae (Diptera: Agromyzidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2HJK]

Mines in upper side of leaf of spear thistle, Cirsium vulgare (Compositae), made by larvae of ragwort leafminer, Chromatomyia syngenesiae (Diptera: Agromyzidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2HJH]

Mines in upper side of leaf of Australian fireweed, Senecio bipinnatisectus (Compositae), made by larvae of ragwort leafminer, Chromatomyia syngenesiae (Diptera: Agromyzidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2HJG]

Leaf mines in Feverfew, Tanacetum parthenium (Compositae), made by larvae of ragwort leafminer, Chromatomyia syngenesiae (Diptera: Agromyzidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2HL8]

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