73.294 Mythimna (Mythimna) straminea (Southern Wainscot)
ws: 31-38mm (MBGBI9.1), fw: 14-18mm (Waring & Townsend); Jul-Aug; common reed (Phragmites australis) reed canary-grass (Phalaris arundinacea); local in marshes and fens in England and Wales, most common in S&SW.England and E.Anglia.
ID: M.straminea and M.impura (Smoky Wainscot) can be very similar to M.pallens (Common Wainscot), but they have a different forewing shape - in M.pallens the forewing base is narrower and the termen makes a steeper angle with costa; M.straminea has a straighter costa and a more pointed apex than M.pallens or M.impura.
M.impura has a straw forewing ground colour; the central vein is white-marked and bordered on its dorsal side with a blackish streak of variable intensity; there may be additional fine black interneural streaks in the terminal part of the forewing; hindwing smoky grey, but sometimes only lightly dusted with grey. Doubtful specimens can be identified by viewing the underside of the forewing which is extensively dusted with blackish scales in M.impura and largely white in M.pallens and M.straminea.
M.straminea has a whitish or greyish-straw forewing ground colour; a diffuse brownish streak runs along the dorsal margin of the central vein; variable dotted postmedian line; hindwing whitish with veins dark-lined and a dark dashed median line (which may be faint). Both M.impura and M.straminea show a dark central spot on the hindwing underside which is usually not present in M.pallens. Having said all that, I usually find the easiest way to recognise M.straminea is by looking at it head-on when it appears to be wearing a headband - due to narrow dark lines across the patagia.
M.impura has a straw forewing ground colour; the central vein is white-marked and bordered on its dorsal side with a blackish streak of variable intensity; there may be additional fine black interneural streaks in the terminal part of the forewing; hindwing smoky grey, but sometimes only lightly dusted with grey. Doubtful specimens can be identified by viewing the underside of the forewing which is extensively dusted with blackish scales in M.impura and largely white in M.pallens and M.straminea.
M.straminea has a whitish or greyish-straw forewing ground colour; a diffuse brownish streak runs along the dorsal margin of the central vein; variable dotted postmedian line; hindwing whitish with veins dark-lined and a dark dashed median line (which may be faint). Both M.impura and M.straminea show a dark central spot on the hindwing underside which is usually not present in M.pallens. Having said all that, I usually find the easiest way to recognise M.straminea is by looking at it head-on when it appears to be wearing a headband - due to narrow dark lines across the patagia.
Male genitalia
Very similar to M.pallens and M.impura. In M.pallens the anterolateral angle of the sacculus is close to 90°, while in M.impura and M.straminea it is more obtuse. In M.pallens the valva expands fairly rapidly from the neck distally and the dorso-lateral angle is rounded, while in M.impura and M.straimnea the valva expands more gradually and the dorso-lateral angle has a small point. In M.straminea the neck of the valva is shorter and the the valva expands more gradually than in M.impura. In M.straminea the dorsolateral angle of the sacculus is more rounded such that the lateral margin of the sacculus appears shorter than in M.impura
Very similar to M.pallens and M.impura. In M.pallens the anterolateral angle of the sacculus is close to 90°, while in M.impura and M.straminea it is more obtuse. In M.pallens the valva expands fairly rapidly from the neck distally and the dorso-lateral angle is rounded, while in M.impura and M.straimnea the valva expands more gradually and the dorso-lateral angle has a small point. In M.straminea the neck of the valva is shorter and the the valva expands more gradually than in M.impura. In M.straminea the dorsolateral angle of the sacculus is more rounded such that the lateral margin of the sacculus appears shorter than in M.impura
Female genitalia
Very similar to M.impura and M.pallens. In M.pallens the sclerotisation of the ductus bursae extends to the junction with the bursa copulatrix, while in M.impura it doesn't extend so far. M.straminea appears intermediate with regard to the above feature and is better distinguished by the shape of the border of the ostium, which is more or less transverse in M.pallens and M.impura but is arched (convex to the posterior) in M.straminea.
Very similar to M.impura and M.pallens. In M.pallens the sclerotisation of the ductus bursae extends to the junction with the bursa copulatrix, while in M.impura it doesn't extend so far. M.straminea appears intermediate with regard to the above feature and is better distinguished by the shape of the border of the ostium, which is more or less transverse in M.pallens and M.impura but is arched (convex to the posterior) in M.straminea.
§1 Ham Fen, Kent; 15/07/2010; fw 16.3mm
§2 Foulness, Essex; 19/07/2014; female
§3 Strumpshaw Fen, Norfolk; 25/07/2014; male; fw 15.7mm
§4 Foulness, Essex; 27/07/2015; male; fw 15.6mm
§5 Foulness, Essex; 26/08/2017
§6 Foulness, Essex; 08/07/2023; male; fw 15.5mm
All images © Chris Lewis
§2 Foulness, Essex; 19/07/2014; female
§3 Strumpshaw Fen, Norfolk; 25/07/2014; male; fw 15.7mm
§4 Foulness, Essex; 27/07/2015; male; fw 15.6mm
§5 Foulness, Essex; 26/08/2017
§6 Foulness, Essex; 08/07/2023; male; fw 15.5mm
All images © Chris Lewis
Page published 27/12/2016 (§1-4) | §5 added 20/04/2018 | §6 added 04/10/2023