066 Acleris laterana (Dark-triangle Button)

TORTRICIDAE | Tortricinae: Tortricini

49.066 Acleris laterana (Dark-triangle Button)

ws: 15-20mm (BTM), fw 7-9mm (Sterling & Parsons), 7.1-9.4mm (my specimens); Aug-Oct; rosaceous trees and shrubs (Crataegus, Prunus, Rosa, Rubus, Sorbus), willows (Salix spp), bilberry (Vaccinium spp); common throughout GB.
Synonyms: Acleris latifasciana (BTM), Argrotoxa comparana (Pierce & Metcalfe)?

Acleris laterana §4 f. labeculana male

ID: Polymorphic and variable. Very similar to A.comariana. A.laterana averages larger (ws 15-20mm vs 13-18mm; fw 7-9mm vs 6-8mm). A.comariana is bivoltine, flying Jun-Jul and Aug-Oct. So specimens obtained in June and July are more likely to be A.comariana; specimens obtained in Aug to Oct with fw>8.5mm are likely to be A.laterana and with fw<7mm should be A.comariana. But as there is considerable overlap in both size and flight season genital dissection is usually required to distinguish these two species.

Form: laterana (uncommon) - ground colour silver white with variable suffusion of grey and black scales; markings red-brown - basal markings diffuse but sub-basal fascia developed on dorsum, costal blotch extending to tornus, its distal edge diffuse; terminal area sprinkled black. This form is similar to A.comariana f. latifasciana (has this been renamed laterana?)
Form: labeculana (common) - ground colour suffused grey; markings red-brown - basal patch represented by a small dorsal portion of the sub-basal fascia, otherwise obsolescent; costal blotch lunate. This form is similar to A.comariana f proteana.
Form: comparana - ground colour pale yellow-brown; markings blackish - same pattern as labeculana. This form is similar to A,comariana f. potentillana
Form: perplexana (common) - ground colour grey-brown, varying considerably in shade; markings brownish - basal patch ?obsolete, costal blotch relatively inconspicuous and may extend to dorsum. This form is similar to A.schalleriana f. castaneana

Male genitalia: The aedeagus of A.laterana has 2 long and several smaller cornuti; that of A.comariana contains no cornuti. Dissection group also mentions that the ventral incision of the sacculus is deeper in A.laterana than in A.comariana, but this is a much less convincing distinguishing feature than that provided by the aedeagus.
Female genitalia: Features differentiating A.comariana from A.laterana are as follows, features of A.comariana are given first:
1. Anterior border of sterigma "W"-shaped with central hump and short lateral points vs "U"-shaped with no central hump and long lateral points;
2. Triangular sclerotisation in antrum absent vs present;
3. Signum present vs absent? The signum of A.comariana is described by Pierce and Metcalfe as a "small scobinate scar" and this is also illustrated in MBGBI5.1 p219 fig.8 and implied by its labelled absence in an image of A.laterana at Moth Dissection - however it is not really apparent in any of the images of the female genitalia of A.comariana at Moth Dissection - so I conclude that features 1. & 2. are more obvious.

Variation
Dissection
Male genitalia
Female genitalia

Form laterana
Form labeculana
Form comparana
Form perplexana

§1 St Marys, Isles of Scilly; 06/09/2009; male; f.comparana?
§2 Ham Fen, Kent; 10/08/2010; male; fw 7.8mm; f.labeculana
§3 St Marys, Isles of Scilly; 28/09/2011; male;
§4 Strumpshaw Fen, Norfolk; 22/08/2012; male; fw 8.7mm; f.labeculana
§5 St Marys, Isles of Scilly; 30/09/2013; female; fw 8.5mm; f.labeculana
§6 Compton Bishop, Somerset; 24/08/2014; fw 8.1mm; f.comparana
§7 Dornie, Ross-shire; 07/09/2014; male; fw 8.5mm; f.labeculana
§8 Dornie, Ross-shire; 09/09/2014; female; fw 8.9mm; f.labeculana
§9 Dornie, Ross-shire; 07/09/2014; male; fw 7.1mm; f.comparana
§10 Dornie, Ross-shire; 08/09/2014; female; fw 9.2mm
§11 Bampton Grange, Cumbria 14/09/2016; male; fw 8.2
§12 Bampton Grange, Cumbria 14/09/2016; female; fw 8.9
§13 Cliburn Moss, Cumbria; 18/09/2019; female; fw 8.0mm
§14 Cliburn Moss, Cumbria; 18/09/2019; female; fw 8.6mm
§15 Pound Wood, Essex; 23/07/2019; female; fw 9.0mm; f.labeculana
§16 Pound Wood, Essex; 23/07/2019; female; fw 9.4mm; f.comparana
§17 Pound Wood, Essex; 23/07/2019; male; fw 8.0mm; f.labeculana
§18 Glen Urquart, Inverness-shire; 18/09/2021; female; fw 8.7mm, f.labeculana
§19 St Mary's, Isles of Scilly; 20/08/2022; male; fw 7.4mm; f.perplexana
§20 Pound Wood, Essex; 18/07/2022; fw 8.8mm f.comparana
§21 Covert Woods, Kent; 15/08/2022; female; fw 8.8mm; f.laterana
All images © Chris Lewis