Spiral Segmentation in Two Species of New Zealand Weta (Orthoptera, Gryllacridoidea, Henicidae)
Two examples of naturally occurring spiral segmentation, one on an immature female specimen of Deinacrida carinata Salmon, and the other on an adult female of Hemideina crassicruris Salmon, are described and illustrated. These are the first examples of this abnormality recorded from the Orthoptera Saltatoria.
Spiral segmentation, sometimes termed helicomerism, has been recorded from orthopterous insects by Cappe de Baillon (1937), who observed it in the phasmid Dixippus morosus (Br.), and by Balazuc (1955), who recorded it from the mantid Mantis religiosa L., in which it had been experimentally induced, and from the earwig Forficula auricularia L., in which it was naturally occurring. This abnormality is well known amongst the Lepidoptera, Hymenoptera, and Diptera, from all of which a number of examples have been described by Cockayne (1929, 1934 et al.) and other authors. In these orders it has been studied in some detail and has been experimentally induced by treatment of eggs with heat, ultra-violet rays or by mechanical stimulation. Balazuc induced it in the mantid by mechanical stimulation of the ootheca. As far as can be ascertained there are no records of spiral segmentation occurring in Orthoptera Saltatoria in the literature, hence the examples described below are the first recorded from this group of insects.
The first is a penultimate stage female Deinacrida carinata Salmon, collected at Herekopare Island, Foveaux Strait, during May, 1954. In this specimen the fourth, fifth, and sixth abdominal segments are helicomerous (Fig. 1). The fifth tergite is the only one which is divided, its right hemitergite being medially fused with the fourth tergite and the left with the sixth tergite. These junctions are indicated by a longitudinal ridge such as normally occurs medially on the fifth, sixth, seventh, and eighth tergites, and which is therefore not a deformity. Apart from this the junctions are almost completely undistorted and lack any sign of previous injury. The sternal region of the abdomen is normal.
The second example is an adult female specimen of Hemideina crassicruris Salmon, captured on Stephen 's Island, Cook Strait, during December, 1954. Here the seventh, eighth and ninth abdominal segments are helicomerous (Fig. II), all the other segments being normal. The right hemitergite of the eighth segment, normal in size, is fused medially with the seventh tergite, and the left hemitergite which is very much smaller and only weakly developed, is medially fused with the ninth tergite. A certain amount of buckling and distortion which has occurred at the junction of these segments, suggests that the abnormality may have been caused by injury to the insect during a juvenile stage. The sternal region is normal.
As Balazuc suggests, helicomerism is rare in the Orthoptera, these examples being the only two encountered during the examination of many specimens of different species of New Zealand weta.
[Footnote] * Prepared during the tenure of a New Zealand University Research Fellowship.
Both specimens are dried and have been placed in the Entomological Collections of the Dominion Museum, Wellington.
Helpful criticism offered by Dr. Salmon during the preparation of this note is gratefully acknowledged.
Balazuc, J., 1955. La T ératologie des Orthopt éroides. A propos de quelques nouveaux faits observationnels et exp érimentaux. Boll. Lab. Ent. agr. Portici, XIV: 48–64, 1 pl.
Cappe de Baillon, P., 1927. R écherches sur la t ératologie des Insectes. Encycl. ent. 8: 291 pp., 85 figs., 9 pls.
Cockayne, E. A., 1929. Spiral and Other Anomalous Forms of Segmentation. Trans. ent. Soc. Lond. LXXVII (II): 177–184, pls. XIII-XV.
—— 1934. Spiral and Other Anomalous Forms of Segmentation with an Account of Three Ventral Spirals in One Brood of Hadena dissimilis Kn. Trans. R. ent. Soc. Lond. LXXXII (I): 165–172, pls. III-V.
Salmon, J. T., 1950 A Revision of the New Zealand Wetas, Anostostominae (Orthoptera: Stenopelmatidae). Dom. Mus. Rec. Ent. 1 (8): 121–177.