49.220 Rhopobota myrtillana (Small Bilberry Marble)
ws: 9-12mm (MBGBI5.2), fw 4.5-6.0mm (Sterling & Parsons); May-Jun; bilberry (Vaccinium myrtillus); NS-B moor heath mountain throughout GB
Synonym: Griselda myrtillana (BTM)
Synonym: Griselda myrtillana (BTM)
ID: Basal and subbasal fascia more or less confluent often forming a dark brown or grey-brown basal patch; median fascia silvery white, variably suffused with plumbeous and brown, its anterior border distinct, posterior border more diffuse; postmedian fascia confluent with tornal patch, dark brown or grey-brown; subterminal fascia silvery-white, variably suffused, from costa at 2/3 to dorsal half of termen; apical patch dark brown crossed by 2 prominent white costal strigulae. Similar to R.stagnana, which averages larger (ws: 10-14mm) and has a discrete subbasal fascia.
Male genitalia: The valva of R.stagnana has a distinct notch at the sacculus-valva junction; there is no such notch in the valva of R.myrtillana.
Female genitalia: Rhopobota species have a prominent sclerotisation at the junction of ductus and bursa copulatrix. This sclerotisation can be interpreted as a pair of side struts connected by a central arc. In R.myrtillana the length of the side struts is relatively short. An attempt at an absolute distinction can be obtained from the following measurements: A) length from anterior apex of side strut to centre of anterior margin of arc, B) width of the sclerotisation at the level of the central arc. A/B is close to 1 and distinctly <1.5 in R.myrtillana and distinctly >1.5 in R.stagnana.
Male genitalia: The valva of R.stagnana has a distinct notch at the sacculus-valva junction; there is no such notch in the valva of R.myrtillana.
Female genitalia: Rhopobota species have a prominent sclerotisation at the junction of ductus and bursa copulatrix. This sclerotisation can be interpreted as a pair of side struts connected by a central arc. In R.myrtillana the length of the side struts is relatively short. An attempt at an absolute distinction can be obtained from the following measurements: A) length from anterior apex of side strut to centre of anterior margin of arc, B) width of the sclerotisation at the level of the central arc. A/B is close to 1 and distinctly <1.5 in R.myrtillana and distinctly >1.5 in R.stagnana.
§1 Knipe Scar, Cumbria; 17/06/2017; male; fw 4.5mm; netted by day
§2 Knipe Scar, Cumbria; 17/06/2017; female; fw 5.0mm; netted by day
§3 Ballindalloch, Moray; 26/06/2021; male; fw 5.0mm
All images © Chris Lewis
§2 Knipe Scar, Cumbria; 17/06/2017; female; fw 5.0mm; netted by day
§3 Ballindalloch, Moray; 26/06/2021; male; fw 5.0mm
All images © Chris Lewis
Page published 16/01/2018 (§1&2) | §3 added 02/09/2021