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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 Malva 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 Malva in Britain.
Chromatomyia
horticola (Goureau, 1851) [Diptera: Agromyzidae].
OR
Chromatomyia
syngenesiae Hardy, 1849 [Diptera: Agromyzidae].
1b >
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 tentatively Malva. Widespread
throughout Britain. Also recorded in the Republic of Ireland.
Widespread in continental Europe.
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