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 'atricornis' has been recorded on Erigeron in Britain.

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

1b > Leaf-miner: Short linear mine in first instar, later producing a circular or oval blotch. Frass is excreted in a black mass prior to pupation. Puparium reddish brown to black, firmly glued with frass within the mine.

On Aster, Bellis and Erigeron in Britain and additional genera of Asteraceae elsewhere. Widespread in southern England and Europe. Also recorded in Canada, Argentina, South Africa, India, Australia and Papua New Guinea.

Calycomyza humeralis (von Roser, 1840) [Diptera: Agromyzidae].

1c > Leaf-miner: A narrow upper surface linear branching mine without apparent feeding lines. Frass in isolated grains and pearl chains. At least in Erigeron, older mines turn reddish brown. Pupation external

On Erigeron acer and Erigeron canadensis in Britain and additional genera of Asteraceae elsewhere. Known only from Warwick in Britain. Widespread in continental Europe.

Phytomyza erigerophila Hering, 1927 [Diptera: Agromyzidae].