Art. XXVI.—The Life-history of some New Zealand Insects: No. 1.
[Read before the Wellington Philosophical Society, 27th October, 1920; received by Editor, 31st December, 1920; issued separately, 20th July, 1921.]
This paper is the first of a series which it is hoped to publish on the biology of New Zealand insects, chiefly those belonging to the Hemiptera. The life-history of not a single species of our endemic Heteroptera has been studied. This is to be regretted, if only because, as Kirkaldy (3) says, “from ovum to adult many of the Hemiptera undergo very remarkable changes of form, much more interesting in reality than the ecdyses of Lepidoptera or other Heteromorpha.” Ctenoneurus hochstetteri Mayr., the subject of this study, is a very abundant member of the family of “flat bugs,” or Aradidae, the species of which, like certain beetles (Brontopriscus) and spiders (Hemicloea spp.) are dorsoventrally flattened in a manner admirably adapted to a subcortical habitat.
I am indebted to Mr. E. B. Levy for the trouble he took in photographing the eggs and insects, and to Mr. David Miller for kindly reading the manuscript and making many valuable suggestions.
Ctenoneurus hochstetteri Mayr. (Hem.-Het.)
Neuroctenus hochstetteri Mayr., Reise der “Novara,” Zool. ii, pl. 4, fig. 47, Hem., p. 166. Crimia attenuata Walk., Cat. Hem.-Het. Brit. Mus., pt. vii, p. 22. Mezira maorica, Walk., loc. cit., p. 28. Neuroctenus hochstetteri Mayr., Hutton, Trans. N.Z. Inst., vol. 30, p. 175, 1898. Ctenoneurus hochstetteri Mayr., Kirkaldy, Trans. N.Z. Inst., vol. 41, p. 25, 1909.
Distribution.—Owing to the lack of collectors interested in Hemiptera, the range of most of the species is unknown. This insect is probably generally distributed throughout the country; it is certainly abundant at Wanganui, Wellington, and Auckland.
Habitat.—Although this bug is abundant beneath almost any loose bark, it shows a decided preference for tawa (Beilschmiedia tawa). This preference is perhaps more due to the looseness of large flakes of bark on dead tawa than to any superiority in the food-supply. Prostrate logs are as much affected as standing stumps, and the number of the insects harboured by them is amazing. Both on the under-surface of the bark and upon the trunk beneath, the massed bugs may form black patches 6 in. or more in diameter, and composed of individuals of various ages, all exuding, especially if crushed, that peculiar and characteristic “buggy” odour familiar to those who have met the bed-bug.
Life-history.—Owing to the difficulty experienced in artificially rearing any specimen through more than a few stadia, this account does not claim to be complete. The early instars live for weeks with very little attention, but the older nymphs and the imagines die with disappointing rapidity.
The Egg (Plate XLIV, fig. 1; text-figs. 1, 2).—Average length, 1.5 mm. It is long, elliptical, and pure-white, the surface rendered beautifully punctate by the reticulation of numerous narrow ridges enclosing regular hexagonal pits. The position of the micropyle was not determined. The ova are deposited promiscuously or in patches on the bark or portions of the trunk, and are gummed lightly by the long axis of the egg. A patch of eggs may measure as much as 4 in. in diameter, and on removal of the bark be visible at 15 or 20 yards distance.
In the laboratory eggs hatched within one month, but that this is the normal period is uncertain. Individuals of most instars are found throughout the season, and the relative periods of the life-cycle probably vary with the time. Eggs hatch as late as April.
Fig. 3.—Second instar, just after first ecdysis. × 35.
Fig. 4.—An intermediate instar. × 11.
Fig. 5.—A late instar. × 8.
Dehiscence of the chorion occurs along approximately two-thirds of one side of the egg to one end, with one or two transverse fissures not extending more than half-way round the egg. Hatching is accompanied by some difficulty, the young nymph carrying the egg-shell for as long as three to six days. The edges of the shell fit round the first segments of the abdomen. The oolemm edges project as a delicate iridescent envelope.
The first instar only is white or colourless, except for a bright yellow area surrounding the orifice of the scent-gland, and caused by the appearance of that gland showing through the transparent exoskeleton. The head is smooth and shining, while the rest of the dorsal surface appears dull.
In October and November the first ecdysis occurs after about six days. The cuticle splits along the mid-dorsal line of the thorax. The second instar shows little structural change; but colour appears as a dark grey on the head, two grey streaks separated by a narrow pale line along the whole dorsal surface, and dark spots on the lateral edges of each segment. The scent-gland opens on a raised area of a dark colour. The individuals of the first and second instars show a habit of standing remarkably high on their legs, a peculiarity noted by Kershaw and Kirkaldy in an Oriental species.
The subsequent nymphal history is marked by an enormous increase in the size of the body relatively to the length of the appendages; by the appearance of spines on the lateral margins of the head; by the growth of tubercles and spots on the posterior margins of the abdominal segments; by the increase of granulation over the whole dorsal surface; and, above all, by the gradual curving of the mesonotal and metanotal posterior margins with the formation of wing-pads, of which those of the mesothorax, forming the rudimentary tegmina, soon cover entirely those of the metathorax. The compound eyes of the second and subsequent instars are brilliant red.
Although Osborn considers five instars to be the normal number in the Hemiptera, Kershaw and Kirkaldy note eight in the case of Dindymus sanguineus Fabr., an Oriental Pyrrohocorid; and there is every indication that Ctenoneurus hochstetteri passes through an equally large number of stadia. The difficulty of ascertaining the exact number of instars may be increased by individual as well as seasonal variation. Such a variation, according to Tillyard, is well known to occur in certain dragon-flies, where the nymphal instars are extremely numerous.
Maternal Solicitude.—Although J. H. Fabre has cast the weight of his authority against the classic example of De Geer's “grey bugs” (Elasmucha grisea) and their display of parental affection, it may be of interest to note that imagines of C. hochstetteri are sometimes found carrying several first or second instar nymphs on their backs and sides in a manner comparable to that of Lycosid spiders. Considering the gregarious habit of the species, perhaps we should rule out maternal solicitude as an explanation; but it is significant that these young nymphs do not apparently cling to older nymphs which closely approach imagines in size.
1. J. C. W. Kershaw and G. W. Kirkalky, On the Metamorphoses of Two Hemiptera-Heteroptera from South China, Ent. Trans., p. 59, 1908.
2. —– Biological Notes on Oriental Hemiptera, No. 1, Jour. Bombay Nat. Hist. Soc., p. 596, 1908.
3. G. W. Kirkaldy, On the Interesting Natune of Heteropterous Metamorphoses, The Entomologist, p. 58. 1908.
4. —– Upon Maternal Solicitude in the Hemipters, &c., The Entomologist, pp. 113–20, 1903.
5. H. Osborn, The Meadow-plant Bug (Miris dolabratus), Jour. Ag. Res., vol. 15, No. 3, 1918.