DAHLIA. Dahlias. [Asteraceae]


Dahlia (Dahlia pinnata) and Garden Dahlia (D. x cultorum) are cultivated in gardens in Britain.

Three Diptera miners, the agromyzids Chromatomyia horticola, Liriomyza bryoniae and Liriomyza strigata are recorded on Dahlia in Britain.

Elsewhere the polyphagous agromyzids Chromatomyia horticola, Chromatomyia syngenesiae, Liriomyza bryoniae, Liriomyza huidobrensis, Liriomyza sativae, Liriomyza strigata and Liriomyza trifolii are recorded mining Dahlia.

No non-Diptera miners are recorded on Dahlia in Britain or elsewhere.

A key to the European miners, based on characteristics of the mines, immature stages and where relevant the larval cases, recorded on Dahlia is provided in Bladmineerders van Europa. This includes Chromatomyiia cf syngenesiae, Liriomyza strigata and Liriomyza bryoniae but not Liriomyza huidobrensis, Liriomyza sativae or Liriomyza trifolii.




Key for the identification of the mines of British Diptera recorded on
Dahlia




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: A distinctive mine primarily above mid-rib, with irregular short lateral offshoots into leaf blade. Pupation external (Spencer, 1972: 51 (fig. 172), 55; Spencer, 1976: 270, 271 (fig. 486)). Branched, whitish, upper-surface corridor; main axis overlying the midrib; side branches overlying the main lateral veins. (In Campanula and Phyteuma the mine is much less branched, sometimes nothing more than a corridor on top of the midrib). Frass in rather long strings. Usually the mines begins as a long and narrow, shallow, tortuous lower-surface corridor that ends upon the midrib but otherwise is not associated with the leaf venation. Often this initial corridor is filled with callus, and then even less conspicuous. Pupation outside the mine (Bladmineerders van Europa). A linear mine on the upper surface, usually following the midrib and showing side branches along the veins. The frass is in strings (British leafminers).

On more than 40 host genera in 15 families in Britain including Dahlia. Widespread throughout Britain. Also recorded in the Republic of Ireland. Widespread in continental Europe.

Liriomyza strigata (Meigen, 1830) [Diptera: Agromyzidae].

1b > Leaf-miner: Mine not primarily above mid-rib.

2

2a > 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 Dahlia 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 Dahlia in Britain.

Chromatomyia 'atricornis' has been recorded on Dahlia in Britain.

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

2b > Leaf-miner: A short, irregular, linear upper surface mine on any part of the leaf, indistinguishable from the mine of Liriomyza sativae. Puparium pale yellowish brown

On 119 plant genera in 31 plant families of which only 4 plant genera in 2 plant families, including Dahlia, are records in Britain. Local, probably introduced to Britain. Widespread in continental Europe particularly in Botanical Gardens and glasshouses. Also recorded in Egypt.

Liriomyza bryoniae (Kaltenbach, 1858) [Diptera: Agromyzidae].



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Last updated 04-Feb-2012  Brian Pitkin Top of page