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LACTUCA. Lettuces. [Asteraceae] |
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Seven species of Lactuca are recorded in Britain. These include the native Least Lettuce (L. saligna), Prickly Lettuce (L. serriola) and Great Lettuce (L. virosa) and the introduced Garden Lettuce (L. sativa) and Blue Lettuce (L. tatarica), Mountain Lettuce (L. perennis) and Pliant Lettuce (L. viminea). Least Lettuce (L. saligna) is protected under Schedule 8 of the Wildlife and Countryside Act, 1981. Two Diptera miner, the polyphagous agromyzids Chromatomyia 'atricornis' and Liriomyza strigata, are recorded on Lactuca in Britain. The polyphagous agromyzids Liriomyza huidobrensis and Liriomyza trifolii have been recorded in quarantine in Britain (Pitkin and Plant in British leafminers).
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Elsewhere the agromyzids Chromatomyia horticola, Chromatomyia syngenesiae, Liriomyza bryoniae, Liriomyza huidobrensis, Liriomyza sativae, Liriomyza scorzonerae, Liriomyza sonchi, Liriomyza strigata, Liriomyza trifolii, Ophiomyia cunctata, Ophiomyia pinguis, Ophiomyia pulicaria and Phytomyza marginella, and the tephritid Trypeta zoe are recorded mining Lactuca. Elsewhere the agromyzid Napomyzxa lateralis is recorded boring stems of Lactuca. One non-Diptera leaf-miner is recorded on Lactuca in Britain (see below). Elsewhere one additional British non-Diptera miner is recorded on Lactuca (see below). |
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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).
Chromatomyia
horticola (Goureau, 1851) [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).
Liriomyza strigata (Meigen, 1830) [Diptera: Agromyzidae]. |
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Key for the identification of the mines of British
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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).
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1a > 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 (Bladmineerders van Europa).
Cnephasia incertana (Treitschke, 1835) [Lepidoptera: Tortricidae] |
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1b > Leaf-miner: The mine begins in the midrib, especially in a lower leaf, extending into the leaf disc, branching irregularly or pinnately, may also locally be blotch like. The mine is brown and very transparent. Sides very irregularly eaten out. Frass loosely dispersed or in a loose central line, buy may also be pressed against the sides of the corridor. The larva may also leave the mine and restart elsewhere (Bladmineerders van Europa).
Orthochaetes setiger (Beck, 1817) [Lepidoptera: Curculionidae] |
| Last updated 05-Feb-2012 Brian Pitkin |  |
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