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

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THYMUS. Garden Thymes. [Lamiaceae]


Six species and subspecies of Thymus are recorded in Britain. These include the native Wild Garden Thyme (T. polytrichus).

Five British miners are recorded on Thymus.

The coleophorid Coleophora lixella is recorded as a seed-feeder on Thymus, although it also mines grasses in Britain and elsewhere.

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



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


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: Blotch mines reaching the edge of the leaf, initially pale green turning brownish white, are caused by the larva feeding on the underside of a leaf (UKMoths). The fully developed case is slender, shining black brown, about 9 mm long. Towards the end a narrow, transparent yellowish ventral keel. Mouth angle 50-60°. Cases on the leaf underside (Bladmineerders van Europa).

On Calamintha, Clinopodium, Glechoma, ? Lycopus, Mentha, Nepeta, Origanum, Prunella, Salvia, Stachys and Thymus in Britain plus Melissa, Melittis and Satureja but not Calamintha elsewhere. Throughout England and Wales and a few places in Scotland. Widespread in continental Europe.

Coleophora albitarsella Zeller, 1849 [Lepidoptera: Coleophoridae].

2b > Leaf-miner and case-bearer: Larva in a slender, brownish black, bivalved sheath case of 7-8 mm. The oral half is tubular, the rear part strongly laterally compressed. Mouth angle 30°. Actually the case only looks like a sheath case. The larva cuts off mined leaves, after having removed the complete leaf margin: what is left is an upper and a lower epidermis, connected by the stub of the petiole. Leaves treated in this way are placed in front of the old case, the stub dorsally, and pointing forwards. The stubs together form a low dorsal keel. The case in fact is a composite leaf case. However, the larva adds so much silk (also because the leaves are too small to form a complete tube) the the leaf fragments are obliterated (Emmet et al., 1996a) (Bladmineerders van Europa).

On Thymus in Britain and elsewhere. Britain including East Kent, North Hants and Surrey. Widespread in continental Europe.

Coleophora niveicostella Zeller, 1839 [Lepidoptera: Coleophoridae].

2c > Leaf-miner and case-bearer: Larva in an untidy composite leaf case of c. 9 mm with a mouth angle of 90°. The larva mines a leaf, usually at the top of a twig, completely out, often while attached to the leaf margin. When the leaf is emptied it is cut off and forms the newest addition to the case (Bladmineerders van Europa).

On Thymus in Britain and elsewhere. Britain including Caernarvon, East Kent and West Cornwall. Widespread in continental Europe.

Coleophora serpylletorum Hering, 1889 [Lepidoptera: Coleophoridae].

2d > Seed-feeder, leaf-miner and case-bearer: Initially it feeds on the seeds of thyme and then uses the seedhead as a case. It overwinters in this case and starts feeding again in March on grass spp. It then makes a case from the mined blade of grass (British leafminers). The larva initially feeds on the seeds of thyme, feeding within a floret and using this as its case. After overwintering, it changes foodplants to grass, and eventually forms an elongated case from two grass blade portions sewn together (UKMoths). The larva begins its life by eating out the ripe fruit of a thyme floret. The emptied and dried calyx functions as its first case, in which it hibernates. After hibernation the larva switches to grasses, initially in its original thyme case. Later a new case is made out of a mined grass leaf. This final case is about 11 mm long, two-valved, straw-coloured, has a mouth angle of 25°, and bears a striking resemblance to a grass spikelet (Bladmineerders van Europa).

On Thymus and the grasses Anthoxanthum odoratum, Briza media, Dactylis glomerata, Holcus lanata and Poa annua in Britain and these grasses plus Alopecurus pratensis, Avenula pubescens, Bromus hordaceus, Elymus and Koeleria elsewhere. Widespread in Britain and continental Europe. Also recorded in the Republic of Ireland.

Coleophora lixella Zeller, 1849 [Lepidoptera: Coleophoridae]

3 > Leaf-miner: Young larvae make small, brown, full depth blotch mines without frass in the young leaves, from within the protection of a spinning. Later they cause upper-surface window feeding, while hidden among spun leaves (Bladmineerders van Europa).

On Thymus in Britain and Mentha, Thymus and Satureja elsewhere. Widespread in Britain and continental Europe. Also recorded in Ireland.

Scrobipalpa artemisiella (Treitschke, 1833) [Lepidoptera: Gelechiidae].



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