{{Short description|Species of moth}} {{Speciesbox | name = Treble-bar | image = Aplocera plagiata01.jpg | genus = Aplocera | species = plagiata | authority = (Linnaeus, 1758) }}

The '''treble-bar''' or '''St. John's wort inchworm''' (''Aplocera plagiata'') is a moth of the family Geometridae. the species was first described by Carl Linnaeus in his 1758 10th edition of ''Systema Naturae''. It is found throughout the Palearctic region and the Near East.

This species varies considerably in size (wingspan 37–43&nbsp;mm) and colouration but is generally grey with three characteristic dark fascia across each forewing, giving it its common name. The hindwings are pale grey or buff. Many forma have been described. See Prout (1912–16) <ref>Prout, L. B. (1912–16). Geometridae. In A. Seitz (ed.) ''The Macrolepidoptera of the World''. The Palaearctic Geometridae, 4. 479 pp. Alfred Kernen, Stuttgart.[https://archive.org/details/macrolepidoptera1216seit pdf]</ref>''Aplocera plagiata'' is difficult to certainly distinguish from its congener ''Aplocera efformata'' See Townsend et al.<ref>Martin C. Townsend, Jon Clifton and Brian Goodey (2010). [https://butterfly-conservation.org/uploads/Difficult_species_guide_page_32.pdf ''British and Irish Moths: An Illustrated Guide to Selected Difficult Species'']. (covering the use of genitalia characters and other features) Butterfly Conservation.</ref><ref>Jaan Viidalepp and Axel Hausmann, 2013 In: Axel Hausmann (Hrsg.): ''The Geometrid Moths of Europe''. 1. Auflage. Volume 3: Larentiinae I. Apollo Books, Stenstrup 2013, {{ISBN|978-90-04-26097-9}}</ref>

One or two broods are produced each year. In the British Isles, the adults can be seen at any time from May to September. The species flies at night and is attracted to light. The egg is whitish, without gloss, micropylar rosette 11- to 12-leaved, the sides with regular polygonal reticulation, each cell again more irregularly subdivided. The larva is also very variable, being green to reddish brown with alternating darker and lighter stripes. It feeds on various species of St John's wort (''Hypericum'' species).<ref>[http://www.nhm.ac.uk/research-curation/research/projects/hostplants/search/index.dsml HOSTS database, National History Museum, London]. Retrieved 2024</ref> It overwinters as a small larva. [[Image:Dieschmetterling14ecks 0435.png|thumb|140px|left|Moth and larrva depicted in ''Die Schmetterlinge Deutschlands'' 10,10a]]

== Subspecies == *''Aplocera plagiata hausmanni'' *''Aplocera plagiata plagiata''

== References == {{Reflist}} *Chinery, Michael ''Collins Guide to the Insects of Britain and Western Europe'' 1986 (Reprinted 1991) *Skinner, Bernard ''Colour Identification Guide to Moths of the British Isles'' 1984

== External links == {{commonscat|Aplocera plagiata}} *[http://www.ukmoths.org.uk/species/aplocera-plagiata/ Treble-bar at ''UKMoths''] *[https://web.archive.org/web/20160303224149/http://www.faunaeur.org/full_results.php?id=444530 ''Fauna Europaea''] *[http://www.lepiforum.de/lepiwiki.pl?Aplocera_Plagiata ''Lepiforum e.V.'']

{{Taxonbar|from=Q1415385}}

Category:Aplocera Category:Moths described in 1758 Category:Moths of Europe Category:Moths of Asia Category:Animal taxa named by Carl Linnaeus