A key to British Sericoderus (Corylophidae)

June 22, 2018 | Author: Anonymous | Category: Science, Biology, Zoology, Entomology
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A key to British Sericoderus (Corylophidae) Mark G. Telfer, 27th January 2012 This key is intended to help with the identification of Sericoderus from Britain. Roger Booth’s discovery of a second species in Britain, brevicornis, has made identification of females problematic. Those problems are gradually being resolved but this document is still a work in progress. Two species of this genus are known from Britain (Johnson, 2008): SERICODERUS Stephens, 1829 brevicornis Matthews, A., 1890 lateralis (Gyllenhal, 1827) 1a. With a small tubercle on the midline of the metasternum. Antennae 11-segmented. Male S. brevicornis. 2 1b. No tubercle on the midline of the metasternum. Antennae 10-segmented. Female. 3 2. Discussion: Sericoderus lateralis is thought to be a parthenogenetic species in Britain and throughout its cosmopolitan distribution. It is conceivable for a normally parthenogenetic species to occasionally produce sexually reproducing individuals. However, Stan Bowestead’s view is that the absence of a sperm duct in female lateralis means that sexual reproduction cannot occur and thus that the existence of males can be discounted. Roger Booth has recently discovered that lateralis females do have a sperm duct, albeit very fine and difficult to see (see below). So a very small possibility exists that a male Sericoderus specimen could be lateralis. 3. NOTE: The spermatheca (Fig. 1) has a globular bulb, a short, straight prong (the ‘apical lobe’) and a long, curved C-shaped tube (the ‘gland duct lobe’). On the bulb, near the base of the gland duct lobe there may be a ‘sperm duct lobe’. Although ‘lobe’ implies something elongate and protruding, in brevicornis the sperm duct lobe is just a tiny blister-shaped structure; Stan Bowestead always uses a compound microscope at 400× to see it.

Fig. 1: Spermatheca of Sericoderus brevicornis redrawn from Bowestead (2003).

© Mark G. Telfer, 2012


The following couplet uses the characters published by Bowestead (2003), modified in the light of subsequent observations. 3a. Sperm duct lobe present. Sperm duct just visible at 25×. Gland duct lobe often1 with a marked preapical constriction. brevicornis 3b. Sperm duct lobe absent. Sperm duct very fine, barely visible at 75×. Gland duct lobe without a marked preapical constriction. lateralis Discussion: In practice, given that dissection and examination of the spermatheca is difficult and time-consuming, any females collected in association with males may be assumed to be brevicornis. But note the assumptions discussed above regarding the identification of males. Roger Booth’s experience, from working with recently collected brevicornis specimens marinaded in 5% acetic acid for a while, is that the sperm duct (a flexible, translucent, membranous tube) is more easily seen than the sperm duct lobe. When dissecting under water, the sperm duct is just visible at 25×. Very recently, Roger Booth (in litt., 23rd Jan. 2012) has dissected some of a series of 48 female lateralis collected at Wicken Fen, Cambridgeshire in 2011 and found that a sperm duct is indeed present! In Roger’s words: “… during dissection of these acetic acid softened specimens, I found that the spermatheca was still joined to the bursa. I could not see anything at 25×, but when I moved the bursa with my forceps, the spermatheca moved too. Even at 75× I could only just make out a very fine tube, which must be the sperm duct. I can now easily imagine that because the sperm duct in lateralis is so very fine, that if one was softening up dried material in NaOH or KOH, it was either being dissolved away or would never be seen, leading to the conclusion that it was absent”. It is worth noting that it is possible to see the sperm duct lobe of brevicornis using a stereomicroscope but probably only with >80× magnification, good optics and good lighting. The lobe is easier to see when you can move the spermatheca around under the microscope than when it is glued into position. Without using a compound microscope, I suspect it would be very difficult to be sure that the sperm duct lobe is absent. Roger Booth has studied Sericoderus females in some detail and noted additional characters in the length of the gland duct lobe of the spermatheca, the length and shininess of the elytra, and the overall body size. These additional characters are presented here for further testing. It is not yet clear how reliable these characters are so if you use this key, please feed back your comments to Roger or I. a. Gland duct lobe much longer, more horseshoe-shaped, encircling an area greater than the bulb. Elytra more elongate, the length is distinctly greater than the maximum breadth across both elytra; shinier. Body averages slightly larger and yellower. brevicornis b.


Gland duct lobe much shorter, more circular, encircling an area more equal to the bulb. Elytra less elongate, the length is only slightly greater than the maximum breadth across both elytra; duller. Body averages slightly smaller and greyer. lateralis

I have added the word ‘often’ as I have seen several female brevicornis with no detectable preapical constriction.

© Mark G. Telfer, 2012


I have recorded Sericoderus 34 times in Britain since I first tackled the genus in 2004. I have only found lateralis once. To the best of my knowledge, other coleopterists such as Peter Hammond and Roger Booth have been finding much the same: lateralis appears now to be greatly outnumbered if not completely replaced by brevicornis, at least in south-east England. Taking all my brevicornis records, I have found 56 males and 42 females and I suspect the population sex ratio would average out at 50:50. It looks as though brevicornis is now the default Sericoderus and any recent records of lateralis need to be carefully verified. Many British coleopterists are probably still regarding lateralis as the default Sericoderus which makes it more difficult to be sure of the current status of lateralis in Britain. As well as the Wicken Fen record mentioned above, Roger Booth (pers. comm., Nov. 2011) still finds lateralis on his patch at Laleham, Middlesex (VC 21), mixed in with brevicornis. Finally, please note that the use of the name brevicornis for the sexual British species is provisional, pending a re-examination of relevant type material (Roger Booth, pers. comm.). Acknowledgements Many thanks to Roger Booth for generously sharing the results of his investigations, to Stan Bowestead for discussion and determining specimens, to Peter Hammond for helpful discussion, and to Arved Lompe for finding the PDF online. References Bowestead, S. (2003). Sericoderus brevicornis Matthews (Coleoptera: Corylophidae) redescribed and new to New Zealand. New Zealand Entomologist, 25 (2002), 65 - 67. [actual publication date February 2003]. Available as a free online PDF: http://www.ento.org.nz/nzentomologist/abstract.php?volume_issue=j25_1&first_page=65 Johnson, C. (2008). Family CORYLOPHIDAE LeConte, 1852. P. 79 in Duff, A.G. (ed.) Checklist of beetles of the British Isles. 2008 edition. Wells: A.G. Duff.

© Mark G. Telfer, 2012


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