Acanthoperga species identification
Image above courtesy of Karin Taylor (iNaturalist observation) CC-BY-NC-ND
Workbook
Can Acanthoperga sawflies in photographs be confidently identified to species level using the original descriptions in the taxonomic literature?
What are the diagnostic features of the 3 Acanthoperga species?
I have constructed a matrix for Acanthoperga spp. drawing on the descriptions in Westwood (1880), Benson (1939), Morice (1919) and Rohwer (1910).
Click on this thumbnail to download a 55KB pdf version.
The images below show some of the body parts referred to in the matrix above.
Critical summary of diagnostic characters of Acanthoperga spp:
A. leucomelas differs from both A. cameronii and A. marlatti in the following characters:
relative length of club and flagellomeres 4+5 - club shorter in A. leucomelas, longer in A. marlatti (flagellum missing in holotype of A. cameronii)
relative breadth/width of postocellar area - broader than long in A. leucomelas vs. longer than broad in A. cameronii, A. marlatti (Benson). Note, however, that Benson’s drawing of A. cameronii head (fig. 25) shows postocellar area being broader than long.
punctation of head in postocellar area - shining spaces between punctures in A. leucomelas vs. finely punctured without shining spaces in-between in A. cameronii and A. marlatti (Benson). Note, however, that Rohwer states that head of A. leucomelas is “dulled by small punctures”.
colour of abdomen above - yellow in A. leucomelas vs. orange-brown in A. cameronii and A. marlatti (Benson). However, Rohwer describes the tergum as “bright reddish-yellow” rather than “yellow” and Westwood’s drawing of A. cameronii shows the dorsum of the abdomen being orange-brown.
infuscation of tip of forewings - not infuscate in A. leucomelas vs. infuscate in A. cameronii and A. marlatti (Benson).
Rohwer states that malar space in A. leucomelas is large, but unclear whether it is larger than in the other species. Benson compares the pedicel length in all 3 species to the length of the malar space, but does not state its absolute size (small vs. large).
Type specimens of A. leucomelas were collected from Kuranda and Cairns, A. marlatti from north-eastern NSW and Brisbane. Purcell and Goolsby have collected A. cameronii from Port Macquarie in NSW to Noosa in Queensland. These were raised from larvae to adults, which were identified by Stefan Schmidt and Ian Naumann.
In summary, geographical distribution, relative length of club and antennomeres 4+5, wing tip infuscation and possibly abdomen dorsum colour are the only differences between A. leucomelas and A. cameronii/A. marlatti which concur with descriptions by different workers and are therefore useable for separation of these species.
A. cameronii differs from A. marlatti in the following characters:
pedicel of antenna is half as long as broad in A. cameronii vs. about as long as broad in A. marlatti (Benson). This is a subtle feature which will only be evident in high quality field photos.
scape and pedicel brown in A. cameronii (Westwood) vs. chocolate in A. marlatti (Benson). This difference is unlikely to be significant. For example, the scape and pedicel on the BOLD specimen of A. marlatti from Stefan Schmidt is dark brown.
A. marlatti has a distinctive chocolate spot/horizontal stripe on the genae behind the eyes, and a chocolate band on the pronotum directly opposite the head stripe, which continues onto the upper half of the pleura and the lateral region of the abdomen (Benson). There is no mention of this feature in descriptions of A. cameronii (Westwood, Benson), so it is assumed to be absent in that species. Rohwer reports a brownish-black region on the pleura just beneath the wings in A. leucomelas.
The hind basitarsus in A. cameronii is only about three-quarters as long as the rest of the tarsal segments together, whereas in A. marlatti it is nearly as long (Benson). This is a difficult character to score accurately in field photos because of potential parallax error.
In summary, pedicel length/width ratio, the presence of a chocolate stripe on the head/pronotum/pleurae and the relative length of the hind basitarsus and remaining tarsal segments are the only characters likely to be useful in field photos to separate A. cameronii and A. marlatti.
Matrix of iNaturalist Acanthoperga observations. Click on this thumbnail to download a 114KB pdf of the full matrix.
Photos of select iNaturalist observations
Conclusions:
None of the iNaturalist observations show the diagnostic features of A. leucomelas, viz. club shorter than flagellomeres 4+5, absence of infuscation on forewing tip and postocellar area broader than long.
All of the specimens in the iNaturalist Acanthoperga observations look very similar to one another. They show at least some of the diagnostic features of A. marlatti which separate it from A. cameronii, viz. pedicel as long as broad; a distinctive chocolate stripe on the genae, directly opposite to a stripe on the pronotum, which is in turn continuous with a stripe on the upper half of the pleura and the lateral region of the abdomen; hind basitarsus nearly as long as the rest of the tarsal segments together.
A caveat is that the original description of A. cameronii is much older (1880 vs. 1939) and far less detailed than for A. marlatti and the holotype specimen is missing its antennal flagella. This adds some uncertainty to the separation of these species by morphology. A strong case can be made for applying DNA barcoding to this problem. As mentioned above, the COI sequence of A. marlatti is already available on BOLD.
References:
Benson, R.B. 1939. A revision of the Australian sawflies of the genus Perga Leach, sens. lat. (Hymenoptera, Symphyta). The Australian Zoologist 9: 324-357.
Morice, F.D. 1919. Notes on Australian sawflies, especially the “Authors' Types” and other specimens in the British Museum of Natural History and the Hope Collections of the Oxford University Museum; with diagnostic synopses of the genera and species, and photographs illustrating their structural characters. Transactions of the Entomological Society of London 66: 247-333, pls XI-XV.
Purcell, M. & Goolsby, J.A. 2005. Herbivorous insects associated with the paperbark Melaleuca quinquenervia and its allies. VI Pergidae. Australian Entomologist 32: 37-48
Rohwer, S.A. 1910. Some Australian sawflies. Entomological News 21: 467-474
Westwood, J.O. 1880. A monograph of the sawflies composing the Australian genus Perga of Leach. Proceedings of the Zoological Society of London 1880: 359-379
This is a workbook page … a part of our website where we record the observations and references used in making species identifications. The notes will not necessarily be complete. They are a record for our own use, but we are happy to share this information with others.