Of the species with which it can be
found together, Trifurcula pallidella resembles T. beirnei most; this can in many cases
be differentiated by the different flying period: T. pallidella occurs from May to early (mid) July, T. beirnei usually in August to September.
However, there are a few earlier records of T.
beirnei, thus July specimens need to be checked carefully. T. beirnei is on average larger (8-11
mm) than T. pallidella, and has three
types of scales (white, yellow and dark tipped). The characteristic gnathos and
large curved valvae of T. beirnei can
often be seen without dissection.
Most other species likely to confuse with T. pallidella belong to the T. immundella complex of species, and of these T. immundella (Zeller, 1839) and T.
chamaecytisi Z. & A. Laštůvka, 1994 resemble T. pallidella most,
but larger and worn specimens of the other species may also be confused. Most
of these species, except T. immundella, feed on the same hosts as pallidella,
and can therefore be found in the same localities. These species are on average
somewhat smaller (6-8.5 mm, sometimes even smaller), and apart from T.
chamaecytisi, they are darker when fresh. In collections T. pallidella was
often confused with the much smaller (5-7 mm) T. serotinella Herrich-Schäffer,
1855. The male genitalia offer the best characters, see images.
Male. Wingspan 7.5-9 mm. Forewing length 3.9 - 4.2 mm (n=10). Head: frontal tuft white to yellowish orange, collar white. Scape yellowish white, sometimes with few darker scales, flagellum yellowish grey; antennae with 42-50 segments. Thorax and forewings white, irrorate with yellow scales; no brown scales present; forewings often predominantly white; cilia concolorous with forewing. Hindwing yellowish white, with some white scales at basis; underside with a terminal 'velvet'-like patch of special scales. Abdomen with three pairs of yellowish abdominal tufts.
Female. Forewing length ca 4.0 mm. Antennae with a least 33 segments (antennae in only specimen examined incomplete). Male genitalia. Capsule length 430-480 µm. Vinculum with ventral plate prolonged anteriorly, shape variable, tegumen triangular. Gnathos with central element truncate or slightly emarginated at tip, lateral arms prolonged anteriorly. Uncus with pointed tip. Valva length 285-300 µm, inner margin not sinuous, dorsal surface excavated for more than half its length; transverse bar of transtilla straight. Aedeagus 390-410 µm long, with single ventral, medial carina, with truncate tip, fused by ventral process to vinculum; vesica with group of long, needle-like cornuti at right side, one long and heavy cornutus, and one strong, curved cornutus in addition to numerous denticulate cornuti. Female genitalia. T8 almost triangular, with more than 10 setae and many scales on either half; anal papillae with 17-18 setae. Anterior and posterior apophyses curved. Vestibulum heavily folded; ductus spermathecae with 3 convolutions.
Larva. Mature larvae about 6-8 mm long, extremely slender, yellow when
fresh. Body almost completely smooth, small spines (microtrichia) absent.
Headcapsule 400-480 μm long, 440-515 μm wide (n=2), much wider than long.
Labrum with 2 pairs of setae; mandibula with 4 strong cusps; labial palpus with
3 segments and long terminal seta, second segment much longer than segment 1 or
3. Prothorax with pair of slender tergites and single indistinct sternite plus
two small sternites anterolateral to the medial one; with the full complement
of 13 pairs of setae. Mesothorax with 12 pairs of setae (D1 present, 4 pairs of
setae ventral to SV1), metathorax with 10 pairs (D1 and L3 absent). Abdominal
segments 1-8 with 6 pairs, A9 with 3 pairs and A10 with 2 pairs. Distribution
of setae illustrated in setal map. Paired ventral ambulatory calli
present on T2-3 and A1-7. Anal rods in A10 posteriorly bifid, forming an angle
of almost 180°.
The larva differs from other described Trifurcula (s. str.)
(Gustafsson 1981; Gustafsson & van Nieukerken 1990) by the large
headcapsule, which is wider than long, the complete absence of microtrichia,
the presence of D1 (named D2 by Gustafsson) on the mesothorax and the labial
palpus which has a very long segment 2, but otherwise confirms with the generic
description. Only Trifurcula (Glaucolepis) headleyella (Stainton, 1854)
and T. (T.) subnitidella (Duponchel, 1843) have also 12 setal pairs on
the mesothorax, the other studied Nepticulidae have only 11 (Gustafsson 1981;
Gustafsson & van Nieukerken 1990; Hoare 2000). No setal map of a species of
Trifurcula (s. str.) had been published previously.
Pupa. Pupal exuviae examined. Frons protruding slightly into conical
projection, eyecaps large, at eclosion torn from frons. Abdominal tergites 2-8
covered with many spines, in about 3 to 5 rows per segment, but not arranged in
distinct rows. Cremaster with two small hooks.
With certainty galls are now recorded from Chamaecytisus albus (Hacq.)
Rothm., C. austriacus (L.) Link, C. hirsutus (L.) Link, C.
ratisbonensis (Schaeffer) Rothm., C. ruthenicus (Fischer ex
Wołoszczak) A. Klásková, Cytisus procumbens (Waldst. & Kit. ex
Willd.) Sprengel (in section Corothamnus) and Lembotropis nigricans
(L.) Griseb.
The galls with full-grown larvae were found from 9 September to early
November. Galls occurred at different heights in the stem, both in older shoots
and younger shoots of the same year. Occasionally two or three galls were found
in the same stem. Old galls remain visible and can still be found in the next
spring, at least until June.
The egg is deposited on the stem where later the gall forms, usually
difficult to see. The larva first bores into the parenchyma and then feeds in a
spiral gallery around the stem, successively moving upwards, also partly boring
in the central woody part of the stem (Figs. 10-16). The stem is thickened more
or less considerably by the larval activity. The diameter of the galls varies
from 3.2-6.0 mm (depending on stem thickness) and the length from 13-26 mm
(n=20). The frass is deposited in the gallery, in a similar
fashion as in stem-mines of related Trifurcula species, almost filling
the gallery.
The full fed larva quits the gall through a slit in its upper part,
usually close to a stem bud (Fig. 14). The pupation takes place in a typical
Nepticulidae cocoon. Cocoon length is 2.7-3.7 mm (mean 3.3 mm, n=20),
width 1.8-2.5 mm (mean 2.1 mm, n=20). Its colour is pale brown to ferruginous
brown. In captivity the cocoons were attached to the walls of the rearing
tubes, to the surface of a stem or on pieces of paper tissue.
Widely distributed in eastern and southern Europe, see countries map and van Nieukerken ety al (2004) and van Nieukerken (2006)
In Poland and Slovakia the species was found in warm and dry grasslands
or open woodland, often on calcareous soils, but also on sand or gravel. In one case (Brzeźno reserve) it was found in a relatively wet habitat on the edge of a calcareous bog.
Elsewhere in Europe it occurs in a variety of habitats, although usually on
relatively warm places: often sunny slopes in river valleys, such as that of
the Danube in Germany, Austria and Hungary. The hosts are frequently associated
with Quercus pubescens woodland. The localities in Corsica, Greece and
Crete are Mediterranean shrubland (garrigue, maquis or phrygana), often close
to the sea. The altitudinal range is from sea level to 1000 m, with one record
at 1600 m in Italy (Imperia, Monesi, Alpi Marittimi).
In
2001 and 2002 the species was extremely abundant in Poland, and larvae could be
found in large numbers in most places. In contrast to that, in October 2004
almost no larvae or galls could be found in several of the same localities.
Most localities in Central Europe are in Nature reserves, and the species may
be vulnerable to increasing pressure by agricultural development and manure.
The galls with full-grown larvae were found from 9 September to early
November. Galls occurred at different heights in the stem, both in older shoots
and younger shoots of the same year. Occasionally two or three galls were found
in the same stem. Old galls remain visible and can still be found in the next
spring, at least until June.
The moths fly in central Europe from 9 May to 19 July, most in May and
June, in southern Greece and Crete they fly from 9 April to 17 May, but also 10
June in northern Greece. The species is clearly univoltine.
After hibernation
in outdoor temperature, the adults emerged from the middle of May to early
June.
This taxonomic description is based on van Nieukerken et al. (1986) & van Nieukreken et al (2004)