Art. XL.—Contributions to the Entomology of New Zealand: No. 8—Parectopa citharoda Meyr. (Order Lepidoptera).
[Read before the Wanganui Philosophical Society, 1st November, 1915.]
Parectopa citharoda Meyr.
Parectopa citharoda Meyr., Trans. N.Z. Inst., vol. 48, p. 418.
Shape.—Oval, wafer-like; base flat; upper portion rounded. The shell appears to extend beyond the egg proper, forming a wide flat transparent mm.
Dimensions.—Total width, 0.40—0.50 mm.; width, excluding rim, 0.28 - 0.35 mm; total length, 0.59 - 0.75 mm.; length, excluding rim, 0.41 - 0.47 mm.; height, about 0.10 mm.
Sculpture.—Devoid of sculpturing, except for very minute white spots (elevations) scattered over the surface of the shell in regular hexagonal formation.
Shell.—Transparent, thin and flexible, but fairly strong; shiny, almost glossy; covered with minute wrinkles.
Colour.—White; the growth of the embryo can be clearly followed.
Note.—The ovae are well cemented to the leaf-surface; are large for the size of the moth. Period of incubation, about fourteen days. (Described 14th February, 1915.)
The eggs are laid indiscriminately on either side of the leaf of the food plant; this follows from the fact that the leaves naturally grow in a vertical position, and there is little, if any, difference between the two surfaces. The eggs are also laid with practically no fixed position between the margin of the leaf and the midrib. There is a distinction, however, in that they are laid invariably on young tender leaves, towards the upper (as opposed to the basal) end. The young seed-pods are also favoured by the parent moth for the deposition of her ovae.
The mine is not difficult to detect, being most conspicuous. It has no definitely fixed position, but often follows the midrib or the margin of the leaf for some distance. It is to be found on either side of the leaf, for the same reason as the deposition of the ovum; for the same reason, also, the larva, when full grown, leaves the leaf from whichever side is most convenient to it. The gallery is long and narrow, in many cases first starting from the site of the egg in a small semicircle and then continues more or less straight till some obstruction is reached, as, for instance, the hard midrib or the margin of the leaf. The obstruction may be followed for some distance, and in this way the mine may become much twisted and contorted. As the larva grows, the mine naturally becomes gradually wider till the last three or four days of the larval existence in the leaf; during this latter period the gallery is much widened, and becomes a large irregular blotch or chamber. The total length of a mine
seldom falls short of 7 in. or 8 in. The deposition of the frass in the mine is an important point for identification. In this case it at first occupies the central portion of the mine, forming a narrow slightly waved line of more or less detached granules, leaving a pale space on either side of it. In some cases this line of frass is continuous without indication of a granular consistency, and looks as if it had been deposited in a soft condition and had run together into a homogeneous thread; at times it is vermiform in character, according to the manner in which the larva was feeding while advancing. This arrangement is suddenly stopped by a break or clear space in the mine, after which the frass granules become more prolific. This continues for some distance, when there is another change—the mine goes deeper into the leaf and becomes choked throughout its whole length with the frass granules. These changes in the character of the frass denote the larval moults. At first the mine is white and in marked contrast to the rest of the leaf, but as moisture gets under the cuticle it becomes much less conspicuous; however, the leaf soon becomes brown along the track of the mine, and so it becomes even more conspicuous than before. The latter portion of the mine is first dark green, but as the frass dries and the cuticle of the leaf withers it becomes dark brown.
1st Stadium.—The prothorax is greatly enlarged; the remaining segments are well rounded, and rapidly diminish in size towards the anus, giving the grub a very attenuated appearance. Colour light green, head light brown. There appear to be none of the primary setae present; to discover these a ¼ in. objective was used without effect. The head is triangular equilateral, flattened, somewhat retractile.
2nd Stadium.—Head large; the cheeks are margined with black; the clypeus has also the black margin, is broad against the labrum, and slightly widens till about two-thirds of its length, when it narrows considerably till it meets the angle formed by the cheeks on the top of the head; mandibles prominent; the cheeks are pale green, with a darker area extending their whole length against the clypeus; labrum dark brown. Prothorax very large, meso- and meta-thorax smaller than the prothorax, the latter smaller than the former, all three flattened dorsally and ventrally. Abdominal segments well rounded, of almost equal size, slightly diminishing towards the anal end, somewhat flattened dorsally and ventrally. Colour light green, darker in centre. Primary setae still absent.
3rd Stadium.—Colour greenish-yellow, a faint white spiracular line. Length just before emerging from leaf (fully extended), about 6.20 mm.; breadth, about 0.90 mm. Body covered with a fine pile. Spiracles circular, minute, very inconspicuous. Prolegs on abdominal segments 3, 4, and 5; armed with single row of 7 brown, well-formed hooks. Primary tubercles bearing short, simple, and in most cases single transparent setae. Tubercle 1 is minute, above ii in the thoracic segments, but some way in front of and below ii in the abdominal segments. ii is well developed. iii is coalesced with two setae on the prothorax, where it is prespiracular; in the meso- and meta-thorax is beneath but in front of i, and has a minute secondary seta above and in front of it, is post-spiracular in the abdominal segments. iv in the prothorax is prespiracular, and is coalesced with a second seta (probably v), is beneath and in front of iii in meso- and meta-thorax, is post-spiracular and behind iii, almost directly beneath ii, in the abdominal segments. v is absent in the meso-, meta-thorax, and abdominal segments. vi appears to be present in the prothorax
in conjunction with vii, but is absent in the other segments. vii is beneath iv in the abdominal segments. (Fig. 1.)
During the first two stadiums the larva burrows close against the outer cuticle of the leaf, but after the second moult descends at once into the parenchyma, gradually eating all that portion of the leaf between the two outer cuticles. It is easy to see where the moults have taken place, not only from the appearance of the frass, as shown in a former paragraph, but also from the fact that at such places the mine is slightly enlarged and the next portion of the mine is directed at a slight angle from the old one, as if the larva had tried to avoid its cast skin, the head-piece of which can be readily distinguished in the clear portion of the mine. After the second moult the mine is at first narrower than before, and is difficult to follow on account of its descending into the denser portion of the leaf (see Fig. 3). The larva appears to undergo only two moults within the mine.
The first two stadiums are of equal duration, being about ten days, though this period may be shortened or lengthened according to meteorological conditions. The 3rd stadium is longer, lasting, on an average, a fortnight. When full-grown the larva leaves the leaf and descends to the ground to pupate.
The cocoons are exceedingly pretty little structures, and their construction is most fascinating to watch under low powers of the microscope. The usual length is 7 mm. and the width varies according to the situation of the cocoon; when constructed on a flat surface it may be as much as 5 mm. The shape is oval and flat. The construction is exceedingly delicate, the cocoon proper having the appearance of a fine white shiny skin The term “cocoon proper” is used because when completed the whole exposed surface is thickly covered with numbers of minute white floccy globules. These look like small bubbles and when seen through the microscope each one has the appearance of being a collection of minute transparent cells, the whole forming a somewhat lengthened sphere. These globules are exceedingly delicate, and many appear to be lightly attached to the cocoon, though numbers can be removed by blowing upon them. The object of this elaborate superstructure is not known.
The globules are ejected from the anal aperture of the larva during the construction of the cocoon proper. The larva takes no notice of the newly ejected globule till it comes across it while weaving the silken canopy; on finding the globule it roughly tears an opening in the structure it has been taking so much trouble in making, and forces it out through the opening so made, not taking the trouble to mend this ugly rent with any degree of care Between seventy and eighty globules are ejected in this way from the cocoon before the work is completed, and these give to it a most curious and beautiful appearance. Watching two larvae constructing their cocoons at the same time, I was astonished to find that the globules were ejected by each at regular intervals of about twenty minutes. Having observed the time of one ejection. I was able to observe subsequent ejections at the minute of the operation throughout the two days during which the cocoons were being constructed. The cocoons are to be found in numbers upon the ground in the dead leaves under the food plant: the smallest and most curved and twisted leaves are the most favoured; even crannies in the lumps of dirt are taken advantage of, besides blades of grass, and sometimes crannies in the bark of the tree itself.
Colour at first almost transparent crystal white, later assuming a light yellow. The eyes are the first to change colour, changing to a reddish-brown; a couple of days or so before emerging the pupa becomes black, excepting those portions that are white in the imago, and the markings on the wings are very plain. The pupa is roughly cylindrical in shape, slightly flattened dorsally and ventrally; the greatest width is opposite the end of the 1st legs; from here the sides converge slightly towards the head, which is broad and well rounded, and somewhat more so towards the last abdominal segments. In profile the dorsal outline is practically straight, head well rounded; between the head and the mesothorax there is a deep incision, at the bottom of which is situated the prothorax.
Ventrally there is a depression opposite the bottom of the eyes, and from here the maxillae and 1st legs and other ventral appendages form a rounded prominence, interrupted by the termination of the 1st legs, from whence the outline gradually follows the antennae towards the anal segments.
Such is the rough outline of the pupa. On top of the head, situated anteriorly, is a small dark prominence used in pushing open the cocoon on the day of emergence. The eyes are fairly large and prominent. The mandibles are present, and occupy two-thirds of the outer edge of the labrum between the eyes; between these, and occupying the remaining margin of the labrum, are the labial palpi; these are well developed, and, though at first slightly constricted, widen out considerably at about half their length, and then gradually taper off. On either side of these, their base resting against the mandibles and a small portion of the eye, are the maxillae; these are very narrow, and are prolonged beyond the labial palpi a short distance. On either side, beneath and somewhat behind the eyes, are the maxillary palpi, forming a sort of eye-collar. Of
this Tutt says, “The palpus on leaving the maxilla passes backwards in the angle between the head and the prothorax, until it is situated deeply beneath the antenna, then it turns forwards to the antenna, and only reaches the surface by emerging from beneath the antenna, and, turning inwards, forms the ‘eye-collar,’ which contains only its terminal joints, the others being concealed deeply.
The 1st legs occupy all the space between the maxilla and the antenna, and even follow the antenna for a short distance; they are fairly broad throughout, and end a little above half the length of the pupa; the terminal joints occupy almost the whole length of the maxillae. The 2nd legs extend along the antennae to about two-thirds of the total length of the pupa, and are broadest opposite the termination of the maxillae. The 3rd legs make their appearance beneath the 2nd legs, and, at first constricted, are fairly wide opposite the end of the wings, and terminate just above the end of the anal segments.
The antennae are narrow, and, commencing above the eyes, extend some distance beyond the terminal segments, more in some pupae than in others; their ends are free; the joints are most conspicuous.
The forewings are broadest opposite the 1st abdominal segment, and rapidly narrow to a narrow, pointed, incurved tip just below the 6th abdominal segment. The hindwings occupy a very narrow strip, which is lost in the 2nd abdominal segment.
The dorsal head-piece is large, prominent, well rounded posteriorly. The prothorax is extremely narrow, and forms a thin sunken strip behind the head-piece. The mesothorax is large and prominent, slightly extended behind. The metathorax is medium-sized. The abdominal segments are of about equal length, and gradually decrease in width towards the anal end. There are indications of a dorsal suture in the metathorax and upper abdominal segments. The free incisions are between segments 5–6, 6–7, 7–8 Segments 8, 9, and 10 appear to be soldered together. Spiracles are minute and raised. There are indications of neuration on the wings.
Duration of pupal stage from specimens obtained in August, twenty-nine days; in December, eleven days.
[The section below cannot be correctly rendered as it contains complex formatting. See the image of the page for a more accurate rendering.]
|Measurement at||Length from Front.||Transverse Diameter||Anterior-posterior Diameter.|
|Top of eye||0.16||0.49||0.55|
|End of labrum||0.35||0.69||0.52|
|" labial palpi||1.18||0.97||0.83|
|" 1st legs||1.94||0.97||0.76|
|" 2nd legs||2.69||0.83||0.72|
|" 3rd legs||4.00||0.28||0.31|
|" last abdominal segment||4.07|
The above measurements are, of course, subject to slight variation.
See page 418 of this volume.
When the imago is matured, and ready for emergence, the pupa forces its anterior segments out of the cocoon. The pupa-case bursts down the centre of the ventral surface; the head-piece, to which the eye-cases and maxillae and palpi are attached, is thrown off, but does not get lost owing to its being held by the tips of the maxillae.
The Australian broad- and narrow-leaved wattles (Acacia pycnantha, Acacia saligna). Indigenous food plants unknown.
Wanganui (M. N. W.), July to March.