CHEIRANTHUS. Wallflower. [Brassicaceae]

Cheiranthus is not recorded Britain, but Wallflowers are common garden plants.

Two polyphagous species, the agromyzid Chromatomyia horticola and the drosophilid Scaptomyza flava are recorded on Cheiranthus in Britain.

The British anthomyiid Delia cardui is recorded on Cheiranthus by Ackland in Chandler (1978), but it is not clear whether this host association is British or Foreign.

The polyphagous agromyzid Liriomyza huidobrensis has been recorded in quarantine in Britain (Dom Collins (pers. comm.)).

Elsewhere the polyphagous agromyzids Liriomyza strigata and the polyphagous drosophilid Scaptomyza flava, are recorded mining Cheiranthus.

No non-Diptera miners are recorded on Cheiranthus in Britain.

Elsewhere one British non-Diptera miner, Ceutorhynchus minutus, is recorded on Cheiranthus (see below). Cnephasia incertana is recorded on Erysimum (including Cheiranthus) in Bladmineerders van Europa) (see below).

A key to the European miners, based on characteristics of the mines, immature stages and where relevant the larval cases, recorded on Erysimum including Cheiranthus is provided in Bladmineerders van Europa. This includes Chromatomyia horticola, Liriomyza brassicae, Liriomyza strigata, Scaptomyza flava, Liriomyza xanthocera, Apterone helicolidella, Ceutorhynchus minutus, Cnephasia incertana, Coleophora onopordiella, Phyllotreta nemorum and Plutella xylostella.

Note: Diptera larvae may live in a corridor mine, a corridor-blotch mine, or a blotch mine, but never in a case, a rolled or folded leaf, a tentiform mine or sandwiched between two more or less circular leaf sections in later instars. Pupation never in a cocoon. All mining Diptera larvae are leg-less maggots without a head capsule (see examples). They never have thoracic or abdominal legs. They do not have chewing mouthparts, although they do have a characteristic cephalo-pharyngeal skeleton (see examples), usually visible internally through the body wall. The larvae lie on their sides within the mine and use their pick-like mouthparts to feed on plant tissue. In some corridor miners frass may lie in two rows on alternate sides of the mine. In order to vacate the mine the fully grown larva cuts an exit slit, which is usually semi-circular (see Liriomyza huidobrensis video). The pupa is formed within the hardened last larval skin or puparium and as a result sheaths enclosing head appendages, wings and legs are not visible externally (see examples).

1a > Leaf-miner: Mine linear, whitish, both upper and lower surface. Pupation internal, at the end of the mine with the anterior spiracles projecting through the epidermis (Spencer, 1976: 433). Upper-surface, less often lower-surface corridor. Frass in isolated grains. Pupation within the mine, in a, usually lower-surface, pupal chamber (Bladmineerders van Europa). A long whitish upper surface corridor, which eventually goes lower surface (British leafminers).

Two highly polyphagous species of Chromatomyia, with indistinguishable mines, have been recorded in Britain. These are syngenesiae (Hardy) and horticola (Goureau) which can only be distinguished by the male genitalia. Both are polyphagous and widespread in Britain and elsewhere, although syngenesiae is almost entirely restricted to Asteraceae (see also 'atricornis').

Chromatomyia horticola is recorded on 55 plant genera in 19 families in Britain including Cheiranthus in Britain.

Chromatomya syngenesiae is recorded in Britain on 27 plant genera in the family Asteraceae and many more genera elsewhere, but not yet on Cheiranthus in Britain.

Chromatomyia horticola (Goureau, 1851) [Diptera: Agromyzidae].
OR
Chromatomyia syngenesiae Hardy, 1849 [Diptera: Agromyzidae].

1b > Leaf-miner: Corridor-blotch mine, normally dorsal; usually whitish; in small leaves it lies characteristically in the centre of the leaf often touching the petiole; in larger leaves it lies to one side of the mid-rib. Frass deposited in green clumps near the leaf margin. Pupation usually external, sometimes in a separate pupation mine.

On numerous genera of Brassicaceae, Asteraceae, Papaveraceae, Resedaceae, Tropaeolaceae and Violaceae, including Cheiranthus, in Britain and additional genera of these families and Fabaceae. Widespread, from Caithness in the north to Cornwall in the south of Britain. Also recorded in the Republic of Ireland, Europe, the East Palaearctic, Near East and Neartic Region.

Scaptomyza flava (Fallén, 1823) [Diptera: Drosophilidae].

1c > Leaf-miner: Leaf and stem mine. Mine always arising from the leaf base or ending in it, because the larva mines and changes leaves. Mine often broad, irregular corridor like, often touching the midrib. At first corridor often entirely without frass, later in the spring the mines are often less deep, containing thick, irregularly deposited frass lumps.

On Cheiranthus, Dianthus and Lychnis and Silene in Britain and/or elsewhere (records ambiguous). Only recorded in Warwick, Easterness and Surrey in Britain. Widespread in continental Europe. Also recorded in the Near East and Nearctic Region.

Delia cardui (Meigen, 1826) [Diptera: Anthomyiidae].

Key for the identification of British non-Diptera mines recorded on
Cheiranthus

Note: The larvae of mining Coleoptera, Hymenoptera and Lepidoptera may live in a corridor mine, a corridor-blotch mine, a blotch mine, a case, a rolled or folded leaf, a tentiform mine or sandwiched between two more or less circular leaf sections in later instars. Larva may pupate in a silk cocoon. The larva may have at least six legs (although they may be reduced or absent), a head capsule and chewing mouthparts with opposable mandibles (see video of a gracillarid larva feeding). Larvae of Hymenoptera and Lepidoptera usually also have abdominal legs (see examples). Frass, if present, never in two rows. Unless feeding externally from within a case the larva usually vacates the mine by chewing an exit hole. Pupa with visible head appendages, wings and legs which lie in sheaths (see examples).

1a > Leaf-miner: Rather small, untidy, full depth, often branched corridor, often close to the leaf margin. Sides irregularly eaten out. Frass in a greyish-green central line that is interrupted from time to time, sometimes partly in strings. In times of rain the frass may run out and appear greenish. Usually several mines in a leaf (Bladmineerders van Europa). The legless larva is rather shapeless, with a well-sclerotised head. The body is whitish; head greyish brown with Y-shaped lighter marking. Pronotum with a pair of brownish shields. The mandibles have two teeth (Bladmineerders van Europa).

Mine of Ceutorhynchus minutus on Raphanus sativus Image: Willem Ellis (Bladmineerders van Europa)

Recorded on numerous genera and species of Brassicaceae, Capparaceae, Resedaceae and Tropaeolaceae, including Cochlearia, but not yet on Cheiranthus, in Britain and Cheiranthus elsewhere. Widespread in Britain and continental Europe. Also recorded in the Republic of Ireland.

Ceutorhynchus minutus (Marsham, 1802) [Coleoptera: Curculionidae]

1b > Leaf-miner: In the first instar the larva mines the leaves, forming short, irregular, blotch-like mines, but in later instars it lives externally, feeding in spun leaves and often twisting those of tender shoots. Larval head light-brown or yellowish brown, edged with black postero-laterally, ocellar area blackish; prothoracic plate black edged with whitish anteriorly; abdomen dull dark green; pinacula distinct, black, sometimes brownish but with black bases to setae; anal plate large, black (Bradley et al., 1973). Small, full depth mine without a definite shape; little frass. Some silk is deposited in the mine. The larva soon leaves the mine and continues feeding among spun leaves (Bladmineerders van Europa).

Recorded on numerous genera and species in several plant families, but not yet on Cheiranthus, in Britain. Recorded on numerous genera and species of several plant families elsewhere, including Cheiranthus. Widespread in Britain and continental Europe. Also recorded from the Channel Is.

Cnephasia incertana (Treitschke, 1835) [Lepidoptera: Tortricidae]