70.133 Perizoma alchemillata (Small Rivulet)
fw: 9-11mm; Jun-Aug; common hemp nettle (Galeiopsis tetrahit); common in England, Wales and lowland Scotland
Perizoma alchemillata (Small Rivulet) §1 female
ID: Similar to P.affinitata (Rivulet) which is larger (fw 12-15mm). Both species have a prominent white cross-band (~distal margin of median fascia) which is divided by a narrow line of brown ground colour. In P.alchemillata the proximal margin of this cross-band usually shows a 'W'-shaped indentation just dorsal to halfway along its length (see inset in forewing picture below); in P.affinitata this indentation is usually 'U'-shaped (this distinction is not absolute - I have found a specimen of P.affinitata with a 'W'-shaped indentation). In P.alchemillata the white band is strong throughout its length on both sides of the narrow brown dividing line; in P.affinitata the distal white line is noticeably weaker (less white) than the proximal white line, especially in its dorsal half. P.alchemillata often shows a more or less distinct double basal white line (~distal margin of sub-basal fascia) which is usually represented by just a short single dorsal line in P.affinitata.
Male genitalia: Only P.affinitata is shown at dissection group. Pierce describes several differences between P.affinitata and P.alchemillata. Features for P.affinitata described first: Labides with head united - head globular vs bilobed; Juxta indented above and below vs narrower above; Uncus tapered, broad at base vs short, pointed; Valva simple vs short. I need to examine more material to properly assess and present these differences.
Female genitalia: According to Pierce, P.alchemillata has a single discoid scobinate signum whilst P.affinitata has two signa, one elongate, ovate and spined the other discoid. Both species are shown at dissection group but this difference is not apparent from the images displayed there. The images of female genitalia below show a single discoid signum.
Male genitalia: Only P.affinitata is shown at dissection group. Pierce describes several differences between P.affinitata and P.alchemillata. Features for P.affinitata described first: Labides with head united - head globular vs bilobed; Juxta indented above and below vs narrower above; Uncus tapered, broad at base vs short, pointed; Valva simple vs short. I need to examine more material to properly assess and present these differences.
Female genitalia: According to Pierce, P.alchemillata has a single discoid scobinate signum whilst P.affinitata has two signa, one elongate, ovate and spined the other discoid. Both species are shown at dissection group but this difference is not apparent from the images displayed there. The images of female genitalia below show a single discoid signum.
Dissection
Male genitalia
Female genitalia
§1 Braemar, Aberdeenshire; 15/07/2011; female; fw 10.6mm
§2 Glen Urquart, Inverness-shire; 18/07/2012; male; fw 10.2mm
§3 Seathwaite, Cumbria; 23/07/2016; female; fw 11.4mm
§4 Thorndon Country Park, Essex; 14/05/2017; male; fw 10.6mm; netted by day
All images © Chris Lewis
§2 Glen Urquart, Inverness-shire; 18/07/2012; male; fw 10.2mm
§3 Seathwaite, Cumbria; 23/07/2016; female; fw 11.4mm
§4 Thorndon Country Park, Essex; 14/05/2017; male; fw 10.6mm; netted by day
All images © Chris Lewis
Page published 01/07/2013 (§1-2) | §3 added 05/07/2017 | §4 added 03/04/2018
