Diagnosis. Male subnitidella differs from other species in the group by the combination of a simple yellow patch and a group of black scales just behind frenulum; further it is one of the smaller and darker species, with less antennal segments than most other species (36 maximum). The male genitalia are well characterized by the gnathos process. Females are smaller and darker than the other described females, and have less antennal segments.
Description. Male. Forewing length 2.0-2.6 mm (2.37 ± 0.17, 44), wingspan 4.2-5.8 mm. Head: frontal tuft yellow-ochre to fuscous, variable; collar similar. Antenna with 31-36 segments (33.4 ± 1.3, 40); scape white, sometimes with few brown scales. Forewing dark greyish-brown to fuscous, slightly irrorated by dark tipped scales, no white spots present; underside with distinct basal patch of deep yellow scales near costa reaching to 1/4. Hindwing: grey, underside along costa directly behind frenulum with a distinct short row of black lamellar scales. Abdomen dark grey, with yellowish grey tufts.
Female. Forewing length 2.0-2.4 mm (2.22 ± 0.16, 9), wingspan 4.4-5.4 mm. Antenna with 27-32 segments (30.4 ± 1.7, 9).
Male genitalia. Capsule length 330-390 µm (349.6 ± 14.8, 15). Vinculum anteriorly rounded. Uncus slightly widened, truncate at tip. Gnathos asymmetrical, central element with an anteriorly curved keel, ending in a pointed process at right side; lateral arms with long and narrow anterior apodemes. Valva length 250-289 µm (264.2 ± 9.0, 15), basally with almost parallel margins, narrowed in middle towards pointed tip. Aedeagus 330-365 µm (344.0 ± 14.0, 15), with ventral carina bifid; aedeagal tube with spatulate tip, dorsal lobe in middle, or slightly on right side, with serrate margin. Vesica with one very long straight, or slightly curved cornutus, with a conical cornutus joined to its basis, and a pointed cornutus with serrations; less then 10 spine-like cornuti and many small cornuti present.
Female genitalia. Terminal segments rather broad; T8 with 3-6 setae and some scales; anal papillae with 11-20 setae each. Ductus spermathecae with 3 1/4 convolutions. Signa 300-355 µm (dorsal) and 350-365 µm (ventral) long.
Final instar larva: long and slender, deep yellow. Head capsule 325-345 µm, 1.13-1.16 x as long as wide, distinctly narrower than in other three described species.
Host plant. Lotus corniculatus L., a common perennial herb of grasslands all over Europe, possibly also on other Lotus species. Cocoon: ochreous.
Widespread in Europe, northward to 60° N, southward to the northern border of the Sahara in Tunisia and eastward to the Crimea and Asia minor. Not yet recorded from Norway, Belgium, Luxembourg, Switzerland, Poland, Hungary, Albania and Portugal, nor from any of the large mediterranean islands. Known from a few specimens from Denmark: NEZ, NWZ and NEJ (on Laesø). In scattered localities in southern Sweden. The species is here for the first time in detail recorded from Finland, The Netherlands, Germany, Czech Republic, France, Spain, Italy, Rumania, Bulgaria, Yugoslavia, Greece, Turkey, Soviet Union (Estonia and Ukraine) and Tunisia.
Life history. The egg is conspicuous and deposited on the stem of the host, usually at the base of a leaf-stalk, frequently near the stem base. The mine is a long gallery in the bark of the stem: the larva is first mining down for 0.5-2 cm, then going up the stem in a rather straight line, or partly encircling the stem, occasionally going down again in the last part of the mine. The mine may reach a total length of 6 to 9 cm. The mine is at first narrow, reddish brown, with straight edges, but later becomes as wide as the stem, with irregular margins, becoming silvery white in fresh mines. Frass deposited in midline, brown, not always well visible. Larva well visible in mine, appearing as a slight swelling.The stems of the host are not killed by the mining activity. The larva quits the mine through a semicircular slit, and spins a cocoon in the soil or on leaf-liter.
Larvae have been taken in September and October, adults fly from May (March in Tunisia) to early September. Reared adults emerged in May. Voltinism not yet clear from these data, clear peaks in flight are not apparent. More data from single localities are needed, and bivoltinism can only be proved by finding larvae and rearing in early summer.
In northern Europe T. subnitidella is almost exclusively found on limestone grasslands (downland) and coastal dunes, in southern Europe it is found in many habitat types. The species might be vulnerable to habitat loss in more northern parts of its occurrence.
This taxonomic description is based on van Nieukerken (1990).