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

 

GEUM. Avens. [Rosaceae]


Five species of Geum are recorded in Britain. These include the native Water Avens (G. rivale), Hybrid Avens (G. x intermedia) and Wood Avens (Geum urbanum). The BSBI provide a downloadable plant crib for Geum.

Eight British miners are recorded on Geum.

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



Key for the identification of the known mines of British
Diptera recorded on Geum


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).

See Key to non-Diptera.


1a > Leaf-miner: Initially a linear mine which later develops into a conspicuous blotch; frass in two rows in linear section, scattered irregularly in the blotch (Spencer, 1976: 134-5, fig. 237, as potentillae).

Corridor, gradually and considerably widening towards the end. Frass in two rows in the corridor part, further up dispersed irregularly. Pupation outside the mine.

A short broad upper surface corridor leading to a long blotch between veins .

On Agrimonia, Filipendula, Fragaria, Geum, Potentilla, Rubus and Sanguisorba in Britain. On additional Rosaceae elsewhere. Common and widespread throughout Britain. Also recorded in the Republic of Ireland, Europe, Japan, U.S.A. and Canada.

Agromyza idaeiana (Hardy, 1853) [Diptera: Agromyzidae].



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


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 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 and case-bearer: The larva lives outside the mine, protected by a case, and feeds on the underlying plant tissues via a hole cut in the epidermis. From that point it eats away as much leaf tissue as it can reach without fully entering the mine. Mine does not contain frass (Coleophora species)

2

1b > Leaf-miner, but not a case-bearer: The larva lives mainly inside the mine. Mine usually contains frass. In later instars the larva may live sandwiched between two more or less circular sections cut from the leaf.

3

2a > Leaf-miner and case-bearer: The case resembles that of C. violacea, but does not lie so flat again the leaf as this species (having a mouth angle of 30 to 50°). C. violacea also has a case which bulges in the middle, whereas in C. potentillae the case tapers towards the posterior . Immediately after emergence the larva makes a full depth, quickly widening, corridor, with frass as small grains in a broad central band. Finally results a blotch of 2 x 5 mm, from which the youth case is cut. The fully developed case is a hairy, greyish brown to silver grey lobe case of about 1 cm long, with a clearly laterally compressed end; the mouth angle is about 90°. The case is difficult to separate from that of C. ochripennella.

On Betula, Agrimonia, Crataegus, Filipendula ulmaria, Fragaria vesca, Geum, Helianthemum nummularium, Potentilla, Prunus spinosa, Rosa, Rubus caesius, Rosa fruticosus and Salix cinerea in Britain plus Malus sylvestris, Ribes, Sanguisorba and Spiraea elsewhere. Widespread in Britain and in continental Europe.

Coleophora potentillae (Elisha, 1885) [Lepidoptera: Coleophoridae].

3a > 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.

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

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

3b > Leaf-miner: Small (less than 1 cm), full depth blotch, transparent when fresh, starting at the leaf margin, usually near the leaf tip; frass in scattered grains. The larva makes an elliptic double sided excision to form a case. Subsequently, it continues feeding within the case.

On Agrimonia, Alchemilla, Filipendula, Fragaria, Geum and Rubus in Britain. On Achillea, Agrimonia, Alchemilla, Filipendula, Fragaria, Geum, Potentilla, Rubus and Spiraea elsewhere. Distributed throughout much of Britain. Widespread in continental Europe.

Incurvaria praelatella (Denis & Schiffermüller, 1775) [Lepidoptera: Incurvariidae].

3c > Leaf-miner: The mine begins with short, rather broad corridor, that often is overrun by the later, large, very transparent full depth blotch. The mine begins somewhere in the centre of the leaf. Frass in many loose grains.

The larvae of sawflies have at least six thoracic legs (although they may be reduced or absent), a head capsule and chewing mouthparts with opposable mandibles but no abdominal legs.

On Geum in Britain and elsewhere. Distribution in Britain unknown. Widespread in continental Europe.

Metallus lanceolatus (C. G. Thomson, 1870) [Hymenoptera: Tenthredinidae].

3d > Leaf-miner: A long gallery with dispersed frass . Oviposition may be at either side of the leaf, not necessarily close to a vein. The mine is a not very tortuous corridor, not widened in the end. Frass in a broad central line. The mine strongly overlaps with the one of S. splendidissimella.

On Agrimonia, Fragaria, Geum, Potentilla and Rubus in Britain plus Geranium elsewhere. Widespread in Britain and continental Europe.

Stigmella aurella (Fabricius, 1775) [Lepidoptera: Nepticulidae].

3e > Leaf-miner: The initial gallery has frass in an interupted black line . Egg usually at the upperside of the leaf. The mine is a long, strongly vein-determined corridor. In the first part the frass lies in a rather narrow, often interrupted central line; further on the frass line is broader and more diffuse. Frequently more than one mine in a leaf.

Mines of Stigmella pretiosa on Geum Image: © Duncan Williams (British leafminers)
Mines of Stigmella pretiosa on Geum
Image: © Duncan Williams (British leafminers)

On Geum and Rubus in Britain and elsewhere. Discovered in Scotland in 1990. It occurs at least as low as 50m in damp, shady riparian Birch and Alder woodland in Sutherland. Widespread in continental Europe.

Stigmella pretiosa (Heinemann, 1862) [Lepidoptera: Nepticulidae].

3f > Leaf-miner: A long sinuous gallery with narrow frass-line . Oviposition generally at the leaf upper side, not especially close to a vein. From there a long and slender corridor starts, with frass usually in a narrow central line. The corridor often crosses itself, but rarely a thick vein.

On Agrimonia, Filipendula, Fragaria, Geum, Potentilla and Rubus in Britain and elsewhere. Widespread in Britain, Ireland and continental Europe.

Stigmella splendidissimella (Herrich-Schäffer, 1855) [Lepidoptera: Nepticulidae].



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