Psednurini, Psednura, and sexing Pyrgomorphidae

Workbook

BACKGROUND

There are two species of Psednura in this region: Psednura pedestris and Psednura musgravei. Although the latter is a more northern species, it has been collected as far south as Merimbula, NSW.

We find these highly cryptic, flightless grasshoppers quite often, and have generally assumed them to be P. pedestris

When we discovered a somewhat different coloured one in Nadgee NP on 25/12/18, we decided to see if we could identify it to species. Surprisingly, on a return visit to the same site the following day we found a second one … larger and greener. We didn’t collect either insect, so we have only a series of photos to go on.

Both sightings are recorded on the Atlas: # 1 - 25th Dec, 2018; # 2 - 26th Dec, 2018

number 1

number 2

I managed to locate a relevant, recent review:

Key, K.H.L. 1972. A revision of the Psednurini (Orthoptera: Pyrgomorphidae). Australian Journal of Zoology - Supplementary Series, Number 14. 1-72

… but it was clear that I’d need the female genitalia to be sure of the species ID.

Step 1: distinguishing males from females

This is not immediately obvious. The general morphology is similar, colour doesn't help, and there is no elongated ovipositor. In addition, most references focus on the internal (ie concealed) copulatory organs, and so I had to hunt about for a diagram of the external features.

Image extracted from Kekeunou et al, page 9 — Image extracted from Kekeunou *et al*, page 9

The way I understand these drawings, the sexes in Pyrgomorphidae can be distinguished based on the following arrangement of terminal structures:

adult male has an unpaired ventral extension ….the sub genital plate. Depending upon the species, it may also have a pair of cerci laterally.
adult female has a stacked set of paired structures … the ventral valves, dorsal valves, and the paraproct. Overlying this, dorsally, may be an unpaired structure … the epiproct.

With references to Kekeunou et al, page 9, I concluded that my insects were: #1 = male, #2 = female

Step 2: which species?

The female (#2) very helpfully displayed her ovipositor while Paul was photographing her. We didn’t handle or dissect her, yet we were able to get a useful lateral view of the valves.

The shape of the dorsal valve, with a prominent row of sclerotised teeth, confirms that insect #2 is indeed P. pedestris.

female ovipositor (lateral view) … image rotated to help with comparison to diagrams 40 & 51 (below)

Given that #1 , the male, was found in exactly the same location, it seems safe to assume that it too is P. pedestris. The only way to absolutely ID the male would be to dissect the genitalia, as the relevant structures are not visible externally.

Further support for #1 being P. pedestris can be found in Key’s description of the species’ biologies (1978, p.65 - see extract below). In summary, P. pedestris would be expected to occupy ‘swampy areas’ and stands of pure sedge or rushes, while P. musgravei tends towards more mixed species vegetation. And the two have not been found together in the exact same habitat. The location of #1 and #2 was alongside a coastal creek, just behind the beach. The vegetation there is almost purely Ficinia nodosa, a Cyperaceae.

This does, however, raise a question about the Psednura we see here at home. The forest vegetation is highly diverse, and not at all ‘swampy’. I’ll be taking a closer look at the next female Psednura we find here!

update - 20th Jan 2019

I’ve been keeping an eye out for Psednura … and at the moment, they’re everywhere! Late afternoon, look among the grasses, and there they are!

Again, Psednura pedestris. The two images below show a single female. The white ‘fluff’ is the pith of the rush she is chewing. The second image shows the sclerotised teeth of the dorsal valve, diagnostic for this species.

And finally a mating pair! Here a second female, in a separate grass patch … and firmly coupled to a much smaller male.
(Note that the colours of this male are almost identical to the colours of ‘insect #1’, described above)

close up of genitalia of mating pair in copulo

Extract from Erichson, W.F. 1842. First description of an Australian pyrgomorph Psednura (Mesops) pedestris.

Apterus, testaceus, capitis thoracisque vitta laterali albidis, femoribus posticis intusrubris, tibiis posticis glaucis basi rubris. — Long. maris ultra 1, fem. prope 2 unc.

Wingless, testaceous (dull brick-red) colour, head and thorax with a lateral white line, hind femora inside red, base of hind tibia bright, shiny red.

Apterus in utroque sexu (both sexes wingless), testaceous, nonnunquam sometimes infra et femoribus posticis facie exteriore virescentibus, forte vivus omnino viridis. Antennae testaceae testaceous, ensiformes sword-shaped. Caput fortiter antrorsum productum, vitta pone oculos laterali albida. Thorax vitta laterali albida. Tegminum et alarum vestigia nulla. Abdomen compressum. Pedes antici brevissimi, postici femoribus intus rubris, tibiis glaucis, basi rubris, tarsis pallidis.

Mas femina plus duplo minor, abdomine spina infra-analilongiore, sensim gradually acuminata pointed, supra concava concave above hastato spear shaped. (Fig.10a.)

Plate 5, Fig. 10 reproduced below.

Screen Shot 2019-02-04 at 10.26.31 am.png

1/5/19

Received 3 insects from Linda Rogan, which she captured near Eltham, following on from an earlier report of these insects on iNaturalist https://www.inaturalist.org/observations/22359083.

lateral view of mouthparts of smallest insect

ventral view of mouthparts of smallest insect

ventral view of mouthparts of smallest insect (prothoracic legs removed)

terminalia of smallest insect - ventral view. Note very long epiproct.

dorsal view of same animal with the long epiproct dissected away.

dorsal view of terminalia - epiproct removed

Why is the subgenital plate in the larger male insect much shorter than in the smaller male insect? Key states that in the male, the instars may be distinguished by the length of the subgenital plate - but doesn’t add anything more. In another Psednurini, Pyrgomorpha vignaudi, the subgenital plate lengthens during nymphal development. At stage 1, its tip is only at the base of the paraproct, whereas by stage 6, its tip has extended well past the paraproct and cerci (Kekeunou et al, 2015).

Note too that the subgenital plate of the male in the mating pair shown above is long, while the epiproct is short. In contrast, the epiproct is long in both of Linda’s males. Key makes no mention as far as I can tell of a difference in the length of the epiproct between instars or geographical locations.

REFERENCES

Erichson, W.F. 1842 Beitrag zur Insecten-Fauna von Vandiemensland, mit besonderer Berücksichtigung der geographischen Verbreitung der Insecten. Archiv für Naturgeschichte 8, 1, 83-287

Key, K.H.L. 1972. A revision of the Psednurini (Orthoptera: Pyrgomorphidae). Australian Journal of Zoology - Supplementary Series, Number 14. 1-72

Kekeunou, S., Mbeng, D., Oumarou-Ngoute, C., & Wandji, A.C. 2015. Morphology, development and reproduction of Pyrgomorpha vignaudii (Orthoptera: Pyrgomorphidae). Entomological Research, 45, 58-70.

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.