04.036 Stigmella myrtillella (Bilberry Dot)
ws: 4-5mm (MBGBI1); bivoltine May-Jun, Aug; larvae Jul and Sep-Oct, mine the leaves of bilberry/bog bilberry (Vaccinium myrtillus/uliginosum); throughout UK where the foodplant grows.
ID: Group B - forewing with a pale fascia but no pale spots. Using the key in MBGBI1 - terminal cilia abruptly whitish beyond a line of dark-tipped scales; fascia yellowish-white, not metallic; apical cilia of forewing more yellow than cilia of hindwing; fascia yellowish (not whitish!), beyond middle, outwardly oblique; basal area of forewing fuscous (with little yellow showing); ws 4-6mm, fascia distinct, aedeagus without long hooked cornuti.
Similar species considered here are all in the Salicis Group of MBGBI1. They all have a ferruginous-yellow head, whitish collar and eye-caps. There are differences in flight season: S.obliquella - May & Aug, S.myrtillella - May-Jun & Aug - so specimens found in Apr and Jul should be S.salicis, those found in Jun should be S.myrtillella, and those found in May & Aug could be any of these three.
S.myrtillella is distinguished in the key in MBGBI1 by having a (narrower) whitish rather than a yellowish fascia! - this seems entirely unconvincing and I think this species would be impossible to separate from S.salicis on external features. As far as I can determine, a difference in habitat/proximity to the foodplant may be the only means of distinguishing adult S.myrtillella/salicis.
Male genitalia: The key and the text in MBGBI mentions that there is a long ventral prolongation of the vinculum in S.myrtillella, but this is not convincingly illustrated in the figures (fig 67, p227 and fig 58, p237) and images at Moth Dissection suggest that this is a variable feature in both species (or perhaps it varies with the degree of compression of the specimen). These illustration show the cornuti to be fairly evenly sized and absent from the apical third of the aedeagus in S.myrtillella, while in S.salicis the cornuti are more variable in size and evenly distributed through the whole aedeagus. Nepticuloidea.info (followed in my Stigmella key) states "usually 5 or 6 cornuti of unequal length" in S.salicis and "usually 3 or 4 cornuti of equal length" in S.myrtillella. However, comparing images of both species at Moth Dissection there does not appear to be any convincing difference in this feature between the species (assuming the specimens are correctly identified). Similarly the gnathos, pseuduncus, transtilla and valval apices appear indistinguishable.
Female genitalia: Not illustrated or described in MBGBI1. Nepticuloidea.info suggests that the species can be distinguished by: S.salicis - anal tufts ½ length of apophyses; ovipositor protruding; corpus bursae with sparse pectination; S.myrtilella - anal tufts ~= length of apophyses; ovipositor slightly protruding; corpus bursae with dense pectination. Only S.salicis is shown at Moth Dissection. The female genitalia shown here as S.myrtillella appear indistinguishable from those at Moth Dissection shown as S.salicis.
Identification of the specimens on this page as S.myrtilella rather than S.salicis is based on an abundant bilberry understory in the predominantly pine and birch woodland at Cliburn Moss. More work to be done assessing genital differences when more material becomes available.
Similar species considered here are all in the Salicis Group of MBGBI1. They all have a ferruginous-yellow head, whitish collar and eye-caps. There are differences in flight season: S.obliquella - May & Aug, S.myrtillella - May-Jun & Aug - so specimens found in Apr and Jul should be S.salicis, those found in Jun should be S.myrtillella, and those found in May & Aug could be any of these three.
S.myrtillella is distinguished in the key in MBGBI1 by having a (narrower) whitish rather than a yellowish fascia! - this seems entirely unconvincing and I think this species would be impossible to separate from S.salicis on external features. As far as I can determine, a difference in habitat/proximity to the foodplant may be the only means of distinguishing adult S.myrtillella/salicis.
Male genitalia: The key and the text in MBGBI mentions that there is a long ventral prolongation of the vinculum in S.myrtillella, but this is not convincingly illustrated in the figures (fig 67, p227 and fig 58, p237) and images at Moth Dissection suggest that this is a variable feature in both species (or perhaps it varies with the degree of compression of the specimen). These illustration show the cornuti to be fairly evenly sized and absent from the apical third of the aedeagus in S.myrtillella, while in S.salicis the cornuti are more variable in size and evenly distributed through the whole aedeagus. Nepticuloidea.info (followed in my Stigmella key) states "usually 5 or 6 cornuti of unequal length" in S.salicis and "usually 3 or 4 cornuti of equal length" in S.myrtillella. However, comparing images of both species at Moth Dissection there does not appear to be any convincing difference in this feature between the species (assuming the specimens are correctly identified). Similarly the gnathos, pseuduncus, transtilla and valval apices appear indistinguishable.
Female genitalia: Not illustrated or described in MBGBI1. Nepticuloidea.info suggests that the species can be distinguished by: S.salicis - anal tufts ½ length of apophyses; ovipositor protruding; corpus bursae with sparse pectination; S.myrtilella - anal tufts ~= length of apophyses; ovipositor slightly protruding; corpus bursae with dense pectination. Only S.salicis is shown at Moth Dissection. The female genitalia shown here as S.myrtillella appear indistinguishable from those at Moth Dissection shown as S.salicis.
Identification of the specimens on this page as S.myrtilella rather than S.salicis is based on an abundant bilberry understory in the predominantly pine and birch woodland at Cliburn Moss. More work to be done assessing genital differences when more material becomes available.
§1 Cliburn Moss, Cumbria; 03/08/2019; male; fw 2.5mm
§2 Cliburn Moss, Cumbria; 03/08/2019; female; fw 2.4mm
§3 Cliburn Moss, Cumbria; 03/08/2019; male; fw 2.5mm
§4 Cliburn Moss, Cumbria; 02/09/2022; male; fw 2.3mm
§5 Cliburn Moss, Cumbria; 14/05/2024; female; fw 2.3mm
All images © Chris Lewis
§2 Cliburn Moss, Cumbria; 03/08/2019; female; fw 2.4mm
§3 Cliburn Moss, Cumbria; 03/08/2019; male; fw 2.5mm
§4 Cliburn Moss, Cumbria; 02/09/2022; male; fw 2.3mm
§5 Cliburn Moss, Cumbria; 14/05/2024; female; fw 2.3mm
All images © Chris Lewis
Page published 24/05/2024 (§1-5)