Ectopsocus briggsi

A common barkfly (despite the absence of records showing on the NBN Atlas), albeit apparently less so than the similar Ectopsocus petersi.

The dark spots on the forewing are usually less obvious than on Ectopsocus petersi but there is considerable overlap and identification on sight is usually difficult, if not impossible. I recommend examination of the abdomens in order to reach a confident identification and find this very much easier if they are well cleared in 10% potassium hydroxide (or similar) first. A high-powered microscope may be necessary, espcially for females.

At the tip of the underside of males of both species there are several patches of dark tubercles, one close to the apex and, slightly basal to this, three in a row. You need to examine the middle one of these three (make sure you're looking at the right patch - I am pretty sure one or two of my earlier attempts at identifying these were confused due to looking at the patch nearer the apex instead). On briggsi this patch is narrow and, looking from the side, vertical-sided whereas on petersi it is broader and more rounded. There is some variation though, and on at least one occasion I have needed to revise my initial identification formed when using the dissecting microscope when I examined it under the compound microscope. Usually it is quite straighforward though...

On this individual the narrow row of tubercles is top centre in the second photo. It can be useful to examine the internal genital structure too, especially on those individuals that are not so clear-cut. These can be difficult to isolate and clean without pulling the various elements apart, although so long as the elements aren't damaged that shouldn't matter. The differences between the two species' genitalia aren't covered at the excellent Barkfly Recording Scheme website, but they are covered by the RES Handbook by T R New (2nd ed 2005). However, there appears to be a mistake with the labelling here, as on page 98 figures 202 and 205 are referred to in the keys for petersi and briggsi respectively wherease the same diagrams (enlarged) appear on page 100 figures 214h and 214g where they are labelled as briggsi and richardsi respectively. I believe the text on page 98 is correct and the caption for figure 214 on page 100 is incorrect.

male Ectopsocus briggsi showing patch of tubercles and genitalia, North Elmham (Norfolk, UK), 29th December 2021

male Ectopsocus briggsi showing genitalia, North Elmham (Norfolk, UK), 29th December 2021 (different individual to the one above)

male Ectopsocus briggsi showing patch of tubercles and genitalia, North Elmham (Norfolk, UK), 2nd October 2021

male Ectopsocus briggsi showing patch of tubercles and genitalia, North Elmham (Norfolk, UK), 23rd February 2022

Females can be tricky - the inner edges of the apical lobes of the subgenital plate are supposed to be parallel in petersi and converging in briggsi, however in my experience they are rarely exactly parallel on petersi and usually converge towards the apexes to a lesser or greater extent. Additionally the tips of these lobes have longer hairs on petersi than on briggsi, but this is not always easy to judge and is also subject to some variation (for example one individual I caught had long hairs on one lobe and short hairs on the other - apparently undamaged).

female Ectopsocus briggsi showing apical lobes of the subgenital plate, North Elmham (Norfolk, UK), 19th September 2021

There apppears to be a second pair of lobes which can be visible behind the first pair. So far as I understand it you only need to view the pair that is most easily visible, although it seems that the second pair can be more obvious (compared to the first pair) in briggsi than in petersi.

female Ectopsocus briggsi showing apical lobes of the subgenital plate, North Elmham (Norfolk, UK), 4th July 2019

female Ectopsocus briggsi showing apical lobes of the subgenital plate, North Elmham (Norfolk, UK), 17th December 2021

Although not consistent there seems to be an average difference in the shape of the edge of the subgenital plate between the bases of the apical lobes, although there is overlap - on briggsi there is usually an obvious central projection whereas on petersi this tends to be much flatter. Also the length and the shape of the apical lobes seems to differ, being longer on briggsi and more curved on briggsi. This can create an almost heart-shaped gap between the lobes which is quite different to anything I have seen on petersi.

female Ectopsocus briggsi showing apical lobes of the subgenital plate, North Elmham (Norfolk, UK), 17th December 2021

female Ectopsocus briggsi showing apical lobes of the subgenital plate, North Elmham (Norfolk, UK), 16th November 2018

The prominence of the central projection between the lobe bases varies between individuals and on this individual it is as small as I have seen it on briggsi, resembling petersi in this respect.

female Ectopsocus briggsi showing apical lobes of the subgenital plate, North Elmham (Norfolk, UK), 11th July 2019

female Ectopsocus briggsi showing apical lobes of the subgenital plate, North Elmham (Norfolk, UK), 1st August 2019

female Ectopsocus briggsi showing apical lobes of the subgenital plate, St Mary's churchyard, North Elmham (Norfolk, UK), 14th January 2022