POLYGONUM. Knotgrass. [Polygonaceae]

Six species of Polygonum are recorded as native to Britain - Equal-leaved Knotgrass (P. arenastrum), Knotgrass (P. aviculare), Northern Knotgrass (P. boreale), Sea Knotgrass (P. maritimum), Ray's Knotgrass (P. oxyspermum) and Cornfield Knotgrass (P. rurivagum). A further two species have been introduced - Lesser Red-knotgrass (P. arenarium) and Red-knotgrass (P. patulum).

Sea Knotgrass (P. maritimum) is protected under Schedule 8 of the Wildlife and Countryside Act, 1981.

Three Diptera miners, the anthomyiids Pegomya betae, Pegomya bicolor and the ephydrid Hydrellia griseola, are recorded on Polygonum in Britain. The record of Pegomya betae requires confirmation.

The British chironomid Cricotopus trifasciatus is recorded on Polygonum by Cranston in Chandler (1978) and the British anthomyiid Pegomya solennis is recorded on Polygonum by Ackland in Chandler (1978), but it is not clear whether these host associations are British or Foreign.

The larvae of a number of species of Chironomidae (see Cricotopus brevipalpis, Criciotopus tricinctus and Cricotopus trifasciatus) live in tunnels in decaying leaf sheaths under water. Their tunnels are open at both ends, and the larvae feed on particles they obtain from a water current they create in the tunnels. They do not feed on tissues of their 'hostplant' and therefore are not strictly miners (Bladmineerders van Europa).

Elsewhere the agromyzids Liriomyza sativae and Liriomyza trifolii and the anthomyiids Pegomya bicolor and Pegomya solennis are recorded mining Polygonum.

One British non-Diptera miner is recorded on Polygonum in Britain and elsewhere (see below).

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: Blotch mines, generally occupying an entire leaf, usually containing several larvae. Much, half deliquescent, green frass The record on Polygonum requires confirmation.

On Atriplex, Beta [Chenopodiaceae] and possibly Polygonum [Polygonaceae] in Britain and additionally Silene and Spinacia [Caryophyllaceae], Chenopodium, Atropa, Hyoscyamus and Solanum [Solanaceae] in continental Europe. Only recorded from Warwick in Britain. Also recorded in the Republic of Ireland, Europe, the East Palaearctic and Nearctic Regions.

Pegomya betae (Curtis, 1847) [Diptera: Anthomyiidae].

1b > Leaf-miner: Leaf mine. Large upper side blotch or blister mine, which can start with a short corridor. In small leaves the mine can be full depth in places. Often several larvae in a mine; frass irregularly scattered in large lumps. Pupation external.

On Persicaria, Polygonum, Rumex and possibly Begonia (record ambiguous) in Britain and in addition Begonia [Begoniaceae] and other genera of Polygonaceae elsewhere. Widespread in Britain. Also recorded in the Republic of Ireland. Widespread in continental Europe. Also recorded in Morocco, Algeria, Tunisia, Syria, Israel, Korea, China and Japan.

Pegomya bicolor (Wiedemann, 1817) [Diptera: Anthomyiidae].

1c > Leaf-miner: Linear mine, becoming a blotch. Two or more larvae feeding together. Frass in lines.

On ? Oxyria, ? Polygonum and Rumex in Britain plus Emex and Persicaria elsewhere. Widespread in Britain. Also recorded in the Republic of Ireland. Widespread in continental Europe.

Pegomya solennis (Meigen, 1826) [Diptera: Anthomyiidae].

1d > Leaf-miner: Irregular mine, locally shallow, elsewhere much deeper, giving it a mottled appearance. In broadleaved plants the mine often begins as a blotch with stellate extensions, but sometimes as a very fine, shallow corridor. In grasses the mine often begins in the leaf sheath. The frass is very fine-grained, initially scattered, later in aggregates.

Mine of Hydrellia griseola on Glyceria fluitans Image: Willem Ellis (Bladmineerders van Europa)

On ? Alisma, ? Damasonium, ? Sagittaria, ? Bellis, ? Rorippa, Tropaeolum , ? Lychnis, ? Stellaria, ? Carex, ? Cyperus, ? Scirpus, ? Hydrocharis, ? Stratiotes, ? Lamium, ? Lemna, ? Allium, Arrhenatherum, ? Polygonum, ? Potamogeton, ? Veronica, ? Typha in Britain and ? Alisma, ? Damasonium, ? Sagittaria, ? Bellis, ? Rorippa, Tropaeolum, Lychnis, ? Stellaria, Carex, ? Scirpus, Trifolium, ? Hydrocharis, Lamium, ? Lemna, Allium, Papaver, Agrostis, Alopecurus, Apera, Arrhenatherum, Avena, Avenula, Brachypodium, Briza, Bromus, Calamagrostis, Dactylis, Desmazeria, Digitaria, Echinochloa, Eleusine, Elymus, Festuca, Gaudinia, Glyceria, Holcus, Hordeum, Lagurus, Lolium, Panicum, Phalaris, Phleum, Phragmites, Poa, Secale, Setaria, Triticum, ? Polygonum, ? Potamogeton, Veronica, ? Typha and Verbena elsewhere. Widespread in England. Also recorded in the Republic of Ireland. Widespread in the Palaearctic region. Also recorded from Nearctic and Australasian Regions.

Hydrellia griseola (Fallén, 1813) [Diptera: Ephydridae].

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

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 at least 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).

1 > Leaf-miner: Initially a gallery is formed, this turning into a blotch, and later two successive conical leaf-rolls (UKMoths). Initially a pale, later brown, usually lower-surface blotch. The blotch is preceded by an epidermal corridor, but that may be obliterated by the later blotch. Silk at the inside of the mine causes it to buckle up a bit and fold. The reddish brown frass is accumulated in a corner of the mine. The older larva leaves the mine and continues feeding inside an untidy cone, made by cutting off a strip of leaf tissue and stitching it in place with silk (Bladmineerders van Europa).

Recorded on Fallopia, Lysimachia, Persicaria, Polygonum and Rumex in Britain and Chenopodium, Lysimachia, Lythrum, Persicaria, Oxyria, Persicaria, Polygonum and Rumex elsewhere. Occurring locally in England, Scotland and parts of Ireland. Widespread in continental Europe.

Calybites phasianipennella (Hübner, 1813) [Lepidoptera: Gracillariidae]