Podacanthus wilkinsoni Macleay, 1881

Common Names:

Lauri's Ring-barker
The Gregarious Phasmid

Identification:

Head above, behind the antennæ, with several impressed longitudinal lines, antennæ twenty-four jointed, about the length of the anterior legs in the male, shorter in the female. Prothorax narrower than the head, and becoming narrower to its junction with the mesothorax, its length being about equal to the length of the head behind the antennæ; the mesothorax is rather narrower and scarcely longer than the prothorax except at its base, where it widens out; it is covered beneath and on the sides with small tubercles, and on the back with a double row of five larger tubercles; the metathorax is longer than the mesothorax, and much wider ; it is sharply tuberculated beneath, as are also, thouglh in a less degree, the abdominal segments. The tegmina are rather pointcd - in the female half the length of the wings, in the male about one-third. The wings are moderately large and equal in both sexes. The legs are rather short; the hind femora strongly dentated beneath on the inner and outer edge, with a deep groove between; the intermediate femora are armed in the same way, but not so strongly; and the anterior are grooved beneath, but not dentated. The basal joint of the tarsi is a little the longest, except in the intermediate legs.

The specimens have been in spirits and therefore it is impossible to make out the colouration with certainty, but the body seems to have been of a reddish-brown, almost black beneath, the wing coverts yellowish, with the median carina brown, the costal area of the wings brownish-yellow, and the wings themselves hyaline, without any visible rosy tint. Length of male three inches six lines; the female is not longer nor bulkier than the male. This uniformity of size in the sexes, if constant, is, I believe, quite unprecedented in this family of insects. (from Macleay, 1881)

the orange to brownish yellow base to the pre-anal part of the wing (the coriaceous “costal field”); the shape of the operculum, which is only very gently curved for most of its length, but sharply so cephalad, and bears a few small laterocephalic teeth; and the emarginate caudal margin of the poculum. (Key, 1957)

is distinguished by the orange-yellow proximal patch on the remigium of the hind wing. (from ?)

Length: 89mm
Coloring:

male and female volant

distinguished by the orange-yellow proximal patch on the remigium of the hind wing.


Campbell & Hadlington, 1967
Male:


Campbell & Hadlington, 1967
Female:


Photo: P. Miller
In this image of a nymph, note the 2 rows of 4 bright red dots (short spines) on the thorax. These are quite prominent on the nymph; they are present but less prominent on the adult. The black dot between the mid - and hind-wings is also prominent on earlier instars, when the wings are less developed.

Lifespan: nypmhs take 3 months to mature, the adult stage a further 3 months.


Campbell & Hadlington, 1967
Eggs: dropped singly on to the forest floor beneath the crown of the tree on which the female is feeding. Most of the eggs hatching in the field are from fertilized females, but a small percentage may develop parthenogenetically. The eggs lie amongst the forest litter for up to eighteen months and sometimes longer before hatching. Generally no development of the embryo is perceptible until the first summer following oviposition, when development takes place though hatching is usually delayed by a diapause until the next spring. In a small number of cases the eggs develop and hatch within one year but some do not hatch until the third season after oviposition. Eggs from unmated females of P. wilkinsoni yielded female individuals only, and thus the parthenogenesis appears to be thelytokous, however it is rare (1.4%). (from Campbell & Hadlington, 1967)

Nymphs hatch between late October and November, usually during the early hours of the morning, if conditions at the time of hatching are very dry or the egg is free to move, the nymph may be unable to free its third pair of legs. There are seven (male) or eight(female) nymphal instars, growth usually being complete by mid-January. (from Campbell & Hadlington, 1967)

Habitat:

arborial, top of host plants (not necessarity top of canopy)

Most of the Eucalyptus species are acceptable as food, though there are preferences within the genus. While no quantitative tests have been done on food preferences it has been noted in nature that the narrow-leaved “peppermints” E. radiata Sieb. and E. robersoni Blakely, the broad-leaved “peppermint” E. dives Schauer and the “gums” E. viminalis Labill., E. huberiana Naud., E. dairympleana Maiden, E. mannifera (A. Cunn. Herb.) Mudie, E. stellulata Sieb., E. pauciflora Sieb., and E. bicostata Maiden, Blakely and Simmonds appear to be favoured species, and are the first to be defoliated. Other species which are known to have been severely defoliated are E. laevopinea R. T. Baker, E. obliqua L'Hérit., E. delegatensis, R. T. Baker, and E. fastigata Deane and Maiden, though these appear to be less favoured than the former groups. E. andreana Naud. is an acceptable species and has been used for most laboratory rearings. Some Eucalyptus species are avoided and these will only be eaten when there is no choice of food. (Campbell & Hadlington)

Similar Species:

Rearing Notes:

Forrestry Commission of N.S.W reared this species for may years while studying it.

Range:

NE coastal, SE coastal, Murray-Darling basin, QLD, NSW

Status:

Not endangered. Known to occur in plage proportions from time to time.

Kentromorphic phase differences have been reported (Key 1957) in the Podacanthus wilkinsoni which sometimes reaches high population densities. In the nymph, the pro-cryptic low-density phase is rather uniform and usually green, whereas the conspicuous, supposedly aposematic, high-density phase is patterned with black, yellow and sometimes white. A mean density of one insect per eucalypt branchiet is sufficient to induce the extreme high-density pattern, while the low- density extreme occurs at less than one per 20 branchlets. Intermediate patterns appear at intermediate densities, or in response to density change. The species also shows morphometric phase differences analogous to those of locusts. There is apparently no correlation between density and activity, and no overt gregariousness. (Key)

References

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