The leaf and stem mines of British flies and other insects
 

(Coleoptera, Diptera, Hymenoptera and Lepidoptera)

by Brian Pitkin, Willem Ellis, Colin Plant and Rob Edmunds

  

CANNABIS. Hemp. [Cannabaceae]

Hemp (Cannabis sativa) is an introduced plant to Britain.

Three British miners plus one species under glass are recorded on Cannabis.

A key to the European miners recorded on Cannabis is provided in Bladmineerders van Europa.

Key for the identification of the known mines of British
insects (Diptera and non-Diptera) recorded on Cannabis

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.

A linear mine on the upper surface, usually following the midrib and showing side branches along the veins. The frass is in strings.

Polyphagous. On more than 40 host genera in 15 families, but not yet on Cannabis in Britain. Widespread throughout Britain. Also recorded in the Republic of Ireland. Widespread in continental Europe.

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

1b > 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, usually in a lower-surface puparial chamber.

A long whitish upper surface corridor, which eventually goes lower surface.

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 species are widespread in Britain and elsewhere, although syngenesiae is almost entirely restricted to Asteraceae. Records on Asteraceae not based on examination of male genitalia are treated in this account as Chromatomyia 'atricornis'.

Chromatomyia horticola is recorded on 160 plant genera in 31 families of which 55 plant genera in 19 families, including Cannabis although not in Britain.

Chromatomyia horticola (Goureau, 1851) [Diptera: Agromyzidae].

1c > Leaf-miner: Mine generally follows the leaf margin, widening from the initial linear section into an irregular broad blotch; it is dark green when fresh but quickly turns blackish (Spencer, 1972b: 34 (fig. 90); Spencer, 1976: 138-9, fig. 246).

Full depth corridor that mostly starts near the leaf margin, and never begins with a series in close, intestine-like curves. Further on the corridor strongly widens, and usually remains close to the leaf margin. Often several larvae in a mine. Frass in lumps or short rods, never in long threads.

Puparium reddish brown

On Urtica, but not yet on Cannabis, in Britain and Humulus and possibly Parietaria eslewhere. Widespread and common in Britain. Also recorded in the Republic of Ireland. Widespread in continental Europe.

Agromyza reptans Fallén, 1823 [Diptera: Agromyzidae].
1d > Leaf miner: Upper-surface corridor. When there is sufficienty space the first part of the corridor is wound in a dense spiral. (This strongly reminds the mine of L. eupatorii, but there the spiral is larger.) Frass, at least partly, in strings. Pupation outside the mine.

The mine starts with a spiral and then becomes more or less straight, mining the upper leaf surface. Frass strings are also evident. The mine looks very similar to L.eupatorii, but in the latter the initial spiral is larger. Future DNA analysis may synonomise these species. This species was first notified to the Plant Health and Seed Inspectorate (APHA) in June 2016 although it seemed to have been present under glass, at secure sites under Home Office license, for 18 months..

On Cannabis (under glass) in Britain. Also recorded on Cannabis from Scandinavia to Slovenia, Serbia and Thrace (Fauna Europaea, 2008).

Liriomyza cannabis Hendel, 1931 [Diptera: Agromyzidae]
 

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