Cockroach nymph — Life in a Southern Forest

Workbook

Cockroach nymphs found in decaying round of wood near wood shed and in house.

Probably belong to the subfamily Blattellinae which have a glandular opening on the seventh tergite and a genital hook on the left side (fig. B, p.198 Rentz).

They look like photos of Robsheldfordia spp. nymphs on p. 242 of Rentz “A Guide to the Cockroaches of Australia”. Males are fully winged and the female tegmina are reduced to small pads and lack hind wings. First abdominal tergum has a pari of shallow depressions.

Locality data make Robsheldfordia circumducta a possible species.

The following panel shows drawings of this species from Roth 1991.

fig.2A,B pronotum male

fig.2D head male

fig.3A male supra-anal plate and paraprocts (ventral)

fig.3B subgenital plate and genitalia (dorsal)

fig.2J front femora (anterior views)

fig.3D hindwing (male)

Or perhaps Johnrehnia australiae p. 223 Rentz and John. Defining feature of this genus is absence of any specialisations of the abdominal tergites and its subfamily

I am attempting to raise #1 through to adult stage to identify it.

found in round of eucalypt wood on 21/1/22

7mm body length

#1 found in bed on 18/2/22 - placed in container (cockroach house) with katydid nymph food

18/2/22

18/2/22 body length 6.8mm

18/2/22

#2 found in kitchen sink on 19/2/22 - added to cockroach house

17/3/22 Discovered that one of the cockroaches, presumably the older, #2, was now an adult with long tegmina.

18/3/22 Placed the container in the freezer to cool the cockroaches down so that I could remove the adult for photography under the Tessovar.

dorsal view

ventral view

dorsal view dissected terminalia

Photos of terminalia show this is a male. Presence of a pair of depressions in first abdominal tergite show that this is a Robsheldfordia sp. Pigmentation of face and pronotum and pattern of femoral spines is consistent with R. circumducta.

#1 11 April

still at nymphal stage or is this a mature female? 2 pairs of wing buds present. According to Rentz, female Robsheldfordia spp. lack hind wings and the tegmina are reduced to small pads. So this suggests this is not that genus.

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