45.006 Platyptilia isodactylus (Hoary Plume)
ws: 19-29mm; Jun-Sep; marsh ragwort (Senecio aquaticus); common in fens and marshes throughout GB
Platyptilia isodactylus §1 male
ID: 3rd lobe of hindwing with a scale-tooth in the fringe; 2nd lobe of forewing ~square-ended, third lobe of hindwing much narrower than first 2 lobes in outer half; scale-tooth weak, linear, half-way along dorsum; saddle paler than thorax > Platyptilia
P.tesseradactyla is small (ws<20mm); P.calodactyla and P.gonodactyla have a prominent dark triangle on the forewing costa.
P.tesseradactyla is small (ws<20mm); P.calodactyla and P.gonodactyla have a prominent dark triangle on the forewing costa.
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Male genitalia: Hart "In all British Platyptilia species the valvae are simple and the uncus is long and tapered. The species can easily be separated by the different shapes of the juxta". Unfortunately, the illustrations in Hart are not entirely consistent with those in Gielis or the images at Moth Dissection AND there appears to be a significant amount of intraspecific variation in the exact shape of the juxta and juxta lobes. The general pattern of the juxta in this genus is a central well sclerotised U (concave posteriorly) with a less well sclerotised juxta lobe extending subapically from the lateral margin of each tine of the U, such that the apices of the U protrude as a short spine (Gielis refers to the juxta as "anellus arms" and interprets each arm as having a central spine). Gielis also mentions and illustrates differences in the shape of the apex of the saccus (in the natural position the saccus is folded over the bases of the valvae, such that its apex is naturally posterior; in slide prep it is unfolded so the the apex is anterior). Looking for consistency amongst all the sources mentioned P.gonodactlya and P.isodactylus may be separable on the following features:
P.gonodactyla: Juxta lobe (A) about same length as distance from midline base of juxta to apex of spine (B): apex of saccus (C) deeply concave P.isodactylus: A/B = ~0.8; C shallowly concave. The best features for P.calodactyla may be that the valvae taper more noticeably and possibly the uncus is stouter (there is no consistency in shape of the juxta in the 3 sources). |
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§1 Pennyghael, Mull; 21/06/2018; male; fw 10.4mm; to light
§2 Corfe, Dorset; 08/09/2020; male; fw 9.2mm
§3 Leworthy, Devon; 31/07/2021; male; fw 9.8mm; to light
All images © Chris Lewis
§2 Corfe, Dorset; 08/09/2020; male; fw 9.2mm
§3 Leworthy, Devon; 31/07/2021; male; fw 9.8mm; to light
All images © Chris Lewis
Page published 02/07/2018 (§1) | §2 added 09/02/2021 | §3 added 21/08/2021
