Tansy Plume Gillmeria ochrodactyla
([Denis & Schiffermüller], 1775)
Wingspan 23-27 mm.
Superficially similar to P. pallidactyla, this species has the hindleg banded brown and white below the middle spurs, and is often more distinctly marked on the forewing.
It occurs, sometimes commonly, over much of England and Wales, and flies in July.
The larvae feed on tansy (Tanacetum vulgare), mining down a shoot, hibernating through the winter in the roots and burrowing up another shoot in the spring.
- Larva: (description Ian F. Smith):
Foodplant: Tanacetum vulgare. August - October, in flowers. November - March, diapauses in rootstock. April, eats into stem of new growth behind a leaf sheath. May and early June, mines stem for about 2 cm, then moves to fresh position on stem, or to a new stem, to mine again.
Early instars Length: 4 mm to 9 mm in late April / early May.
Head: Pitchy brown or black. Paler anterior. Mouthparts reddish brown. Stemmata and stemmatal area black.
Prothoracic shield: Pitchy black, divided by fine greenish white medial line.
Thoracic legs: Dark brown with black marks.
Body: Ground colour whitish; slightly tinted green, most noticeably on thorax and venter. Coarsely shagreened. Reddish brown dorsal, dorso-lateral and spiracular lines, which expand and meet intersegmentally, the dorsal line appearing as a series of kite-shape marks on the abdomen. The lines are present, but less distinct, on segments T2 and T3. The colour of the lines is due to a combination of yellowish brown integument and dark reddish brown shagreen granules.
Spiracles: Pitchy brown.
Pinacula: Fully developed, dark grey, shiny, sclerotised pinacula with two setae and two black setal spots are found on segment A9 and below the spiracles on A1 to A8. Most other pinacula consist mainly of a unisetose black setal spot with an insignificant sclerotised grey periphery, visible only under magnification.
Setae: Translucent grey.
Anal segment (A10): No anal comb. Anal plate, pitchy black.
Prolegs: Transparent. Slightly tinted light green. Planta thin. Crochets black. Large blackish lateral sclerite on anal prolegs.
Penultimate instar Length: 11 mm. May.
Head: Pale green. Epicranial spheres overlaid yellowish. Mouthparts reddish brown. Stemmatal area black.
Prothoracic shield: Pale green. Row of six setae at anterior and another six further back. Base of seta pale so setal spot forms a small peripheral black ring.
Thoracic legs: Pale green transparent. Claw brown.
Body: Matches colour of T. vulgare stem. Ground colour pale green, translucent, shagreened. Greyish green dorsal, dorso-lateral and spiracular lines. The lines are present, but less distinct, on segments T2 and T3. The colour of the lines is due to a combination of grey-black shagreen granules and a short stubble of black secondary setae. The dorsal line is intensified by the darker green of the contractile dorsal vessel. White subspiracular line and whitish subdorsal and lateral lines, discontinuous intersegmentally.
Spiracles: Strong black peritreme Surrounded by collar of integument lacking grey-black granules and black secondary setae, so paler than rest of spiracular line.
Pinacula: Fully developed, whitish, shiny, sclerotised pinacula with two setae and two black setal spots are found on segment A9. Most other pinacula consist mainly of a black setal spot, with any whitish sclerotised periphery obscured by the white lines on which they are located.
Setae: Primary setae are translucent whitish, set in a black setal spot, which forms a ring round the base of the seta. Brown setae on anal plate. Thick stubble of black secondary setae on dark lines of body.
Anal segment (A10): No anal comb. Anal plate, whitish green with light brown setal spots.
Prolegs: Transparent. Concolorous with venter. Planta thin. Crochets black with tips reflected upwards.
Final instar Length: 14 mm. Late May or early June.
Head: Whitish yellow. Frons whitish. Mouthparts reddish brown. Stemmatal area black.
Prothoracic shield: Translucent, clouded whitish, variously showing whitish yellow of head or pale green of body. When the larva is viewed superficially from above, the prothoracic shield can be mistaken for the head, which is often held down and concealed from view. Row of six setae at anterior and another six further back. Base of seta pale so setal spot forms a small peripheral black ring.
Thoracic legs: Pale green, transparent. Claw brown.
Body: Matches colour of T. vulgare stem. Ground colour pale green, translucent, shagreened. Dorsal, dorso-lateral and spiracular lines slightly darker green, barely perceptible, as the grey-black shagreen granules and short stubble of black secondary setae are much sparser than in previous instar. The dorsal line is the sole noticeable dark line because of the darker green of the contractile dorsal vessel. Strong white subspiracular line on A1 to A8, less distinct on T2 and T3. Fainter whitish subdorsal line, discontinuous intersegmentally. Indistinct, fragmentary, whitish lateral line. Ventrally pale green.
Spiracles: Pitchy black.
Pinacula: Sclerotised pinacula on segment A9 concolorous with integument, so only perceptible by shiny reflection and their black setal spots. Most other pinacula consist mainly of a black setal spot, with any whitish sclerotised periphery obscured by the white integument on which they are located.
Setae: Primary setae are translucent whitish or pale grey, set in a black setal spot, which forms a ring round the base of the seta. Brown setae on anal plate. Sparse stubble of black secondary setae on darker parts of body. Colourless secondary setae ventrally.
Anal segment (A10): No anal comb. Anal plate, brownish yellow with light brown setal spots.
Prolegs: Transparent. Concolorous with venter. Planta thin. Crochets pitchy black with tips reflected upwards.
Pupa: 14 mm. Attached by reddish cremaster to stem, or to dead or live leaves of T. vulgare. Slender, with pronounced subdorsal keels and anterior beak. Slender extended case on wing apex / antenna. Two colour forms occur: i) Light greenish ground colour heavily marked brown , matching the colours of dead T. vulgare leaves. Dorsal line dark brown. Dark brown subdorsal spot on each abdominal segment. Subdorsal keel, white and most pronounced on head and thorax, ochrous brown on abdomen, extending to segment A3. Dark brown dorsolateral line and supraspiracular line with hooked expansions round spiracles. Strong dark brown subventral and ventral lines. Beak dark brown. Wing case veins whitish yellow, cells brown. Wing apex case combined with antennal case, long and thin, whitish. ii) Light green with faint vestiges of the markings described above, matching the colour of live T. vulgare. However, sometimes green pupae are found on dead foliage and brown pupae on live plant parts . An example of the green variety was observed to retain its colour until two days before emergence, when it turned uniformly yellowish brown.
Similar species: The main foodplants recorded for Platyptilia pallidactyla are Achillea spp., but it has also been found feeding, and reared, on Tanacetum vulgare (by R.J. Heckford, in litt.), where it can be confused with P. ochrodactyla larvae. In a description of P. pallidactyla (C. Hart, in litt.) the main distinguishing features of the otherwise similar larva appear to be its smaller size; 12 mm fully grown, and external feeding instead of mining by the mature larva.
Search techniques: Look for wilted, even slightly, new shoots of Tanacetum vulgare (tansy). These are most easily found in late April, when shoots are relatively equal in height at about 30 cm. Later, occupied shoots are often stunted and hidden by unaffected growth and by other plants, which need to be parted in the search. River embankments are a likely situation, the larvae often favouring plants sheltered by adjacent trees or bushes. Gently pull back the leaf sheaths from the stalk. If you see traces of frass, look closer for the larva of P. ochrodactyla, often protruding from a short excavation in the stem in late April or, later, just visible down its boring in the stem.