Mosquitoes of the Auckland District.
[Read before the Auckland Institute, 2nd October, 1928; received by Editor, 12th February, 1929; issued separately, 15th August, 1929.]
The present paper is the first result of studies carried out by aid of a research grant originally made by the New Zealand Institute and the Department of Health, and later renewed and increased by the former. The grants were made to the Auckland Mosquito Control Committee, under whose direction the present writer has conducted his studies.
The paper contains descriptions of adults, eggs, larvae and pupae of three mosquitoes found commonly in and around the City of Auckland, and of the habits associated with each stage.
The three species are Aedes (Finlaya) notoscriptus (Skuse), Culex pervigilans Bergroth and Rachionotomyia argyropus Walker, the last of which presents most unusual, if not unique larval habits.
Aedes (Finlaya) notoscriptus (Skuse), 1888, Edwards, 1922.
- Culex notoscriptus Skuse (W. Macleay MSS.) Proc. Linn. Soc., N.S.W. (2), 3, p. 1738, 1888.
- Stegomyia notoscriptus (S.), Theobald, Mono. Culic., 1, p. 286, 1901.
- ——, Giles, Handbook Gnats, 2nd Ed., p. 371, 1902.
- ——, Theobald, Mono. Culic., 3, p. 145, 1903.
- Ann. Mus. Nation. Hung., 3, p. 76, 1905.
- Scutomyia notoscriptus (S.), Theobald, Gen. Ins. Culic., p. 19, 1905.
- Mono Culic., 4, p. 198, 1907.
- —— Bancroft, Ann. Q'ld. Mus., No. 8, p. 24, 1908.
- ——, Theobald, Mono. Culic., 5, p. 200, 1910.
- Ochlerotatus notoscriptus (S.), Edwards, Ann. Mag. Nat. Hist., (8), 9, p. 523, 1912.
- Scutomyia notoscriptus (S.), Taylor, Trans. Ento. Soc. Lond., 1913, pt. 4, p. 686; 1914, p. 191 (1915).
- Proc. Linn. Soc. N.S.W., 39, p. 457, 1914, (1915).
- Ochlerotatus notoscriptus (S.), Taylor, Proc. Linn. Soc. N.S.W., 43, pt. 4, p. 834, 1918.
- ——, Miller, N.Z. Dept. of Health Bull., No. 3, (1920).
- Aedes (Finlaya) notoscriptus (S.), Edwards, Bull. Entom. Res., 13, pt. 1, p. 100, 1922.
- ——, Edwards, Bull. Entom. Res., vol. 14, pt. 4, 1924.
General Coloration. Head black, thorax dark brown or black, with a distinctive lyre-shaped thoracic pattern. Abdomen black with white basal and lateral patches. Legs black, some tarsi white, with white patches on joints of some legs.
Female. (Fig. 1): Head black, black-scaled, occiput and nape carrying many upright forked scales. Proboscis length 2 ½ mm.,
half length of body, black, with a silvery-white band in the middle; labella lighter in colour. Palpi black, scaled, black bristles, apex with fine silvery-white scales; a peculiar raised papilla on penultimate segment (Fig. 2). Clypeus black. Torus black anteriorly, with a number of scales on inner margin; posteriorly golden brown.
Antennae thirteen-jointed, length same as proboscis, (2.5 mm.); black, flagellar segment lighter in colour, covered with short black hairs and scattered longer black verticillate hairs. Eyes greenish-black, with a golden sheen; a band of golden scales below the eyes; a longitudinal row of golden scales from nape to frons. Occiput
and nape covered with black scales and upright forked black hairs.
Thorax umber-brown to almost black; numerous blackish-bronze coloured spindle-shaped scales; round the margins are numerous long black bristles. One median silvery and sometimes golden line running from cervix to two-thirds distant posteriorly when it bifurcates and continues to scutellum. Two short medio-lateral lines made up of golden hairs; these continue posteriorly to one-third length of thorax. Two lateral curved lines of golden hairs, which also run to scutellum; lateral again to these are two other thin lines of silvery-white. Scutellum trilobed, black except a stripe of flat silvery-white scales situated basally. Five bristles on median lobe, three on lateral lobe. Metanotum pale brown. Halteres with a pale stem and knob, black patch on inner and upper margin.
Pleural pilotaxy (Fig. 3): Protergum is dark brown in colour, carrying 8 to 10 strong light-coloured pronotal bristles and a band of silvery-white scales. Pro-episternum golden yellow in colour, carrying 6 to 12 strong prosternal bristles; on the posterior end are several white scales. Pro-epimeron carries two pro-epimeral bristles covering the first spiracular, black scales and white scales
are scattered about the posterior margin. Spiracular area has 6 to 8 bristles, but in no way do they cover the first spiracle, black scales are present and a band of white scales on lower margin; between this area and the mesepisternum is a patch of white scales.
Fig. 2.—Palpus of ♀.
Fig. 3.—Pleural pilotaxy of A. notoscriptus.
Fig. 4.—White pleural scales.
Fig. 5.—Pleural scales.
Mesepisternum carries 10 to 20 pre-alar bristles; its posterior margin is bordered by a fringe of sterno-pleural bristles: several patches of white scales are also present. Mesepimeron has a large number of upper mesepimeral bristles; two patches of white scales are also present, these are broad and short (Fig. 4). The black scales are crescentic (Fig. 5).
Legs—Fore-leg: coxa and trochanta pale; femur black, pale at base, with a line of white scales down each side; knee joint white. Tibia black, with a line of white scales along each side. First and second tarsals black with a broad white proximal band; third tarsal black, with a few white scales at basal end; fourth and fifth tarsals black. Mid-leg: black, with much wider band of white scales along entire, length, and an apical patch of white scales. Tibia black, with the same longitudinal white band and a faint white band near proximal joint. First tarsal with white basal patch. Second with large white basal band. Third, fourth and fifth black. Hind-leg: femur black, with line of white scales along each side; knee joint white, tibia with much broader white line, which, however finishes at apical two-thirds. Tarsal joints: first and second
with broad white basal band and faint apical band, third and fourth with white basal band only, fifth all white except for a few brown scales at apex. Hind tarsus half as long again as the others. Ungues of fore-leg long, almost straight and simple, Ungues of mid-leg shorter than fore and more curved. Ungues of hind-leg simple, smaller than others, with signs of a rudimentary tooth (Fig. 6).
Wings (Fig. 7) 4.5 mm. long. Veins covered with black scales. Cell R.2 much longer and narrower than cell M.2, base of cell R.2 almost level with that of M.2, if anything a little nearer the base of the wing stem, less than one-third the length of the fork cell. Cell M.2 about one and one-third times the length of stem. Posterior cross vein twice its own length distant from the mid cross vein.
Fig. 7.—Wing of Aedes notoscriptus.
Fig. 8.—Fringe scales.
Fig. 9.—Median vein scales.
Fig. 10.—Lateral vein scales.
Fringe scales (Fig. 8) long, tapered and curved, lighter in colour than vein scales (Figs. 9 and 10); median vein scales (Fig. 9) broad and shorter than lateral (Fig. 10).
Male: Head similar to that of female, but with a distinct stripe of silvery-white scales round the eyes, and a patch of golden scales on the frons. Palpi longer than proboscis, brown, with dark brown scales basally, these becoming darker towards apex; patches or bands of white scales on last two joints. Proboscis black, a white band on base of the apical half; length 5 mm. Antennae brown, verticils silky brown; penultimate and antepenultimate segments long. Ungues of fore and mid-leg unequal and toothed (Fig. 11). Ungues of hind-leg with a trace of a small tooth.
Hypopygium (Fig. 12) long and broad at base slightly tapering posteriorly. Dorsal surface with scattered long setae and scales; the internal border of basal and sub-apical lobes covered with bristles pointing internally. Clasper narrow, tapering to a fine point; no claw or spine. Arising from the harpago area are two
long curved tapering moderately chitinised appendages which reach to two-thirds or more of the length of the lobes. Phallosome bristly.
This species differs from either of the other two being described in this paper in the thoracic ornamentation, the white banded legs and the white ring at the centre of the proboscis. It is found in New Zealand from Nelson to Auckland. It is ordinarily a sylvan species, being plentiful in shrubberies and gullies especially where the sunlight strikes through the foliage. Skuse (1888 p. 1740) describes this species as being occasionally found in houses, but in Auckland it is a frequent intruder. It is a purely daytime biter, early morning and late afternoon being the most favoured times, except on dull days, when it bites at any time.
Aedes (Finlaya) notoscriptus flies very quietly and does not hover around before biting as does Culex pervigilans; moreover it settles on a person's legs much more frequently than on the hands and face. It is a persistent attacker, returning again and again when driven off. It exhibits a marked preference for settling on a dark material, a preference which I have often tested; when flying, it stretches the hind-legs behind the body (as does Culex pervigilans), while Rachionotomyia argyropus, the third species described in this paper, spread its legs out laterally when in flight.
Farmers of Clevedon who have cattle grazing in the bush in the winter and spring say that black and white mosquitoes (presumably A. notoscriptus) are so numerous there in warm weather that they cause the cattle to seek the open country to escape their bites, and drovers have stated that, when conducting sheep past swamps, both they and the stock have been severely attacked by mosquitoes, the sheep being bitten on the nose and ears to such an extent as to cause a mild stampede. In Mercer, dairy-farmers have had to burn cowdung to ward off the persistent attacks of a black and white mosquite
during milking; they say that the severity of the attacks is such as to diminish the milk yield, and add that the mosquitoes bite the cows in preference to the milkers.
Eggs and Oviposition.
Skuse (1888 p. 1740), describes the eggs of this species as being hatched from boat-shaped masses of nearly 300 eggs; but this is now known to be incorrect. They are laid singly, though they may, and often do, run together forming star-shaped masses, but they never lie side by side to form rows as described in the case of Culex pervigilans. Any two eggs approaching to within a quarter of an inch of each other will at once run together and become attached by their ends, not by their sides. The eggs are light in colour when first laid, but become black after two or three hours' exposure. The surface presents a matt appearance under a low power; this may be due to air bubbles, for when they are shaken in water the matt surface is lost and they sink to the bottom, but this does not interfere in any
way with the hatching of the larvae. When the egg has lost its matt surface, the dark black colour is replaced by dark brown. In form (Fig. 13) they are navicular, slightly more pointed at one end than the other, the micropyle being at the less acute end.
|Length of egg||.625 mm.|
|Greatest width||.2 mm.|
These eggs are not easy to find, for they occur in natural or artificial water containers in sheltered positions, in hollows in rocks, especially those occurring in caves, in knot- and rot-holes in such trees as mahoe (Melicytus ramiflorus) tawhero (Weinmannia racemosa), pohutukawa (Metrosideros excelsa), kowhai (Sophora tetraptera) and puriri (Vitex littoralis); in the axils of nikau leaves (both on the palm and on the ground), Astelia, and in banana palms in gardens and conservatories; in barrels, tanks and troughs in the shade of buildings, trees, shrubs or long grass, and in standing water in conservatories or ferneries. I have also found them in drains, swamps and water-holes, but this is exceptional. These eggs are only found in still and stagnant water, rich in organic matter from the overhanging vegetation, and I have observed by placing tins with clear and stagnant water side by side that the female of this species has a strong preference for the stagnant water for oviposition, a
preference more marked than in the case of Culex pervigilans. Similar observations demonstrated her preference for shade. A most unusual breeding place for this species was in fire buckets on the Papakura railway station, a most open and windy situation.
The egg takes from 36 to 72 hours to develop and hatch, temperature largely controlling the rate; when the eggs are immersed they take twenty-four hours longer to hatch. These eggs are not laid until the last week in October in the Auckland district, and then only in a few warm locations, but in November and onwards to May large numbers are laid; after May they decrease in numbers and in June eggs are seldom seen. I have not observed the egg-laying of this easily disturbed species, although I have kept them in cages in the laboratory, and I am therefore unable to state whether oviposition takes place in daylight or at night.
The larvae of this species can be distinguished from those of the other species described, by the siphon which is short and barrel-shaped, while that of the others is much longer; the antenna has one antennal hair plume which is situated on the apical two-thirds. This larva, with drawings of the terminal segments, has been described by Cooling (1920 p. 21); but for the convenience of New Zealand observers the writer proposes to figure it in more detail from New Zealand specimens. The larva is of a darker colour than that of
Culex pervigilans, and very little variation in depth of colour has been observed. Length of larva in fourth instar—6 to 7 mm., without siphon.
Head (Fig. 14) dark, almost black, chitinised, slightly narrower than thorax, front rounded, slightly expanded laterally at the level of the antennae, posterior margin rounded. Pre-clypeal hairs short, stout at base, tapering, bent sharply inwards almost at right angles and sharply-pointed. Pre-antennals fairly long and pointed. Outer anterior clypeal hairs consist of three sets of trifid and quadrifid branches of simple hairs, which reach almost to the proximal third of the antennae. One trifid tuft of simple hairs is situated posteriorly and centrally to the antennae. One anterior ocular and one posterior ocular quadruple tuft. Eye moon-shaped, fairly large, Maculation absent.
Antennae almost cylindrical, infuscated, antennal plume a single hair situated approximately at the apical two-thirds, in length reaching half the balance of the distance to the terminal. The terminal hairs are composed of one long and two shorter ones; a short spine-like process arising from a papilla is also present.
Mentum (Fig. 15) index 2.2: 1.10, triangular in shape, one central tooth at the apex, much larger than the side teeth. Eleven smaller incurved teeth each side, these teeth decrease in size posteriorly, the last one being very much smaller than the others.
Fig. 15.—Mentum of larva of A. notoscriptus.
Fig. 16.—Maxillae of larva.
Fig. 17.—Mandible of larva.
Base much crenulated symmetrically. Maxilla (Fig. 16) ovate with rounded apex, one strong spine on the outer margin, numerous diverging hairs arise from near the apex; one strong process on the inner margin. Mandible (Fig. 17) quadrangular. On the outer margin is a pair of strong, elongated recurved spines, pointing upwards; immediately below is a rounded stumpy spine or process. The premandible has one large tooth and three smaller below; along its upper surface and below the margin is a line of strong recurved hairs, which continue across to the opposite margin. Five short strong spines on posterior margin.
Thorax from above (Fig. 18) not much wider than head, angulated, mesothoracic and metathoracic chaetotaxy composed of groups
of long spinose hairs which are found arising from slightly chitinised papillae; several short sharp spines stand in close proximity to the hairs also. For ventral chaetotaxy see Fig. 19.
Abdominal segments on the dorso-lateral margin of each is one long bifid hair, minutely pubescent on the proximal third; these
hairs decrease in length on each successive segment posteriorly, several short trifid, bifid, and single hairs are to be seen on the angulations of each segment. Terminal segments (Fig. 20): lateral comb on the eighth comprises 30 to 36 scales in a triangular mass, not in regular lines; each scale (Fig. 21) has a fringe of fine hairs on the widest part of the free margins. Several single, bifid, trifid and quadrifid hairs are seen on this segment, all simple. Siphonal plume a quadruple tuft almost as long as anal segment, simple. Sub-siphonal plume same as last. Anal plume a single hair also simple.
Siphon infuscated, barrel-shaped, chitinised, twice as long as broad, siphon index 1.6: 0.9, slightly tapered after the apical two-thirds; the siphonal valve large and prominent, several hairs on the outer and inner margins. Pecten consists of 13 to 18 strong spines, which run up more than half the length of the siphon, increasing in size distally, terminated by one tuft of three simple hairs. Each spine (Fig. 22) has a circular base and the apex sharply pointed, and bears three small and one larger spinelet. Arcus present, but small.
Anal segment not completely invested with anal saddle, strongly chitinised; on the distal portion of the saddle are several fine small spines. Sub-dorsal hairs as follows: two long strong hairs one on each side arising from a strong papilla, five other shorter strong hairs also arising from papillae, but only two-thirds the length of the former on the dorsal margin are several black strong short spines. Lateral hair (Barraud) is a bifid tuft and as Cooling remarks is sometimes quadruple, but seldom seen. The ventral beard consists of 10 to 12 groups of simple hairs, similar in length to the shorter dorsal hairs. Anal gills: the two dorsal gills are half the length of the sub-dorsal hairs, the ventral are shorter by a third, but in some instances I have seen them equal in length; they have been noted by other observers to be liable to variation; they are blunt at the apex, and rather wide up to the distal two-thirds, then sharply tapering.
The larva of Aedes notoscriptus hangs from the surface of the water at an angle of 75°, and its movement is of a serpentine nature by which it can easily be distinguished from the other species described herein. It bears a very close resemblance to that of Aedes (Ochlerotatus) antipodeus, but the former has a more barrel-shaped siphon, while the latter has a more rounded head with the antennae more curved, and a more horizontal, but still sinuous movement in the water.
A. notoscriptus and C. pervigilans are occasionally found breeding together, but the locality in these instances is always of the type characteristic of the former. It shows a decided preference for the darkest parts of water containers. I have frequently looked for it in troughs and have found plenty of C. pervigilans but very few A. notoscriptus. One day, however, on examining the covered-in part of a trough, where the ball-cock is protected by a covering, I found them concentrated there in large numbers. In an old barrel
left in a shrubbery at Muriwai I found this larva to number over 500 to the pint of surface water.
It is very susceptible to light and sound, the least light from a torch or the shadow of a person is sufficient to cause it to sink to the bottom, and it will remain there much longer than the larva of Culex pervigilans. Even after a long interval it comes to the surface very warily, and at the least shadow will descend again. It is able to remain under the water longer than the larvae of Culex pervigilans.
The pupa of this species is smaller than that of either of the others described. Colour, light brown. Length 4.5 to 5 mm. Paddle (Fig. 23), index 1.8: 2.1, ovoid, with a terminal bifid hair, which distinguishes it from the other species. Last abdominal segment with a tuft of four to six branched hairs (Fig. 23) on the latero-dorsal margin; a single hair more centrally situated. On the
penultimate segment, dorsally situated, are two bifid and four single simple hairs. Breathing trumpet (Fig. 24) square-shaped. Length of life 2 to 4 days in summer-time, extending to 6 in colder weather. The pupa hangs from the surface with abdominal segments at almost right angles to the surface of the water.
Culex pervigilans Bergroth.
Culex pervigilans Bergroth, Wiener entom. Zeitung, 1889, p. 295.
—— Theobald, Mono. Culic. of the World, vol. 2, pp. 88–90.
—— Miller, N.Z. Dept. of Health Bull. No. 3, 1920.
—— Edwards, Synopsis of Mosquitoes of Australasian Region (1924) p. 124.
General Coloration.—Thorax dark brown, densely covered with golden scales arranged longitudinally; traces of two curved longitudinal lines, especially when denuded of scales and bristles. Abdomen black, with white basal bands; venter white-scaled. Legs black, white spots at knee joints of femora. Ungues of female small, simple and much curved; of the male, uniserrated in fore and mid legs, in the hind, simple.
Female (Fig. 25). Head: Nape and occiput covered with golden-yellow curved scales; numerous black upturned curved bristles at the margins. Proboscis dark brown, darker at apex, lighter at base, strongly haired and scaled. Length 2 ½ mm. Palpi (Fig. 26) dark brown, 4-jointed, thick in appearance; penultimate joint curved inwardly, as long as next two, heavily scaled and bristly; in length one-
fifth of proboscis; basal joint almost black in some specimens. Antennae dark brown, almost black. Eyes deep purplish-black: strong black bristles around margins.
Thorax dark brown, covered with golden-yellow scales arranged in longitudinal rows; numerous black bristles about the median and marginal areas. Scutellum light brown, narrow curved scales and 8 border bristles. Metanotum dark brown. Pleura dark brown.
Pleural pilotaxy (Fig. 27) as follows: Protergum carrying 3 to 8 pronotal bristles. Pro-episternum has three prosternal bristles. Pro-epimeron carries 2 to 4 (usually 3) strong pro-epimeral bristles covering and guarding the first spiracle; numerous golden sickle-shaped hairs anterior to these. Spiracular area bare. Mesepisternum carries 3 to 6 pre-alar bristles, 6 to 10 sternopleural bristles on the posterior margin arranged vertically. Many white scales are present
on the area between the pre-alar and sternopleural bristles. Mesepimeron has 4 upper mesepirmeral bristles covering and guarding second spiracle; below these is a patch of white scales; one lower mesepimeral bristle. Coxa pale brown, with black bristles and odd white scales.
Legs dark brown, in parts almost black, heavily scaled and bristled. Femur dark brown dorsally, light brown ventrally, bristled, knee spot almost white. Tibia with pale knee joint, more heavily bristled than femora and slightly longer. Tarsus darker brown than the other joints. Ungues equal, simple, much curved, but showing a strong raised swelling basally. (Fig. 28).
Wings (Fig. 29) 4.5 mm. in length; when folded back longer than abdomen; densely clothed along the veins with brown scales.
Cell R.2 (first marginal cell) longer and narrower than cell M.2 (second posterior cell), its base more proximal than the base of the latter, its stem short, almost one-fifth the length of cell, shorter than stem of M.2, which is a little more than one-third the length of cell. Supernumerary and mid cross veins slightly separate, about half their own length away from each other. Posterior cross vein longer
Fig. 29.—Wing of C. pervigilans.
Fig. 30.—Lateral scale of wing vein.
Fig. 31.—Median vein scale.
Fig. 32.—Fringe scale of wing.
than mid cross vein and twice its own length distant proximally from it. Lateral scales (Fig. 30) of medium width, tapered distally; median scales (Fig. 31) broader, rounded distally; fringe scales (Fig. 32) scimitar-shaped. Halteres with light brown stem, knob darker in colour and a black patch on each side. Length 5.6 mm.
Male: Antennae lighter in colour than in female; the penultimate and antepenultimate joints longer, hairs brown in colour. Proboscis darker than in female, sometimes pale in centre. Palpi much longer than proboscis, last two joints with stiff black hairs.
Hypopygium (Fig. 33) large and composed of many appendages, the dorsal surface of the sub-apical lobe covered with numerous strong bristles pointing out to external border. The sub-apical lobe has a leaf-like appendage lying across from internal border to external border; it overlies the base of a strong stiff curved bristle which springs from the inner margin of the sub-apical lobe and points upwards and outwards. On the external border of this lobe are three chitinous tapered appendages turned backwards towards the phallosome. The claspers are long, “goose-necked,” and carry a narrow pointed claspette. Harpago and harpaginal fold can be seen by reference to the figure. Ungues of male fore-leg (Fig. 34) unequal, curved, proximally there is a small acute recurved spur; at the middle length is a longer blunt appendage. The fifth tarsal joint is heavily bristled and scaled; its base is expanded to form a strongly curved and acutely pointed projection.
Length, 6 mm.
Habitat, New Zealand; it is not yet certainly known elsewhere.
This is the common domestic mosquito in New Zealand. It is found in both Islands wherever there are human habitations, climatic conditions being no deterrent to its breeding; it is found from the sea coast to the inland mountains. It is purely a nocturnal feeder. There is no definite seasonal occurrence; it is found in abundance one
week, apparently disappears for a while, and then suddenly and unaccountably reappears. It breeds through the whole of the winter in Auckland city and suburbs, and as far south as Mercer, residents of which parts are pestered with its painful bites throughout the whole of the year. Some do, however, shelter for a while in the coldest weather in cellars, stoves, pig pens, stables and buildings, lying quietly close up to the walls with the legs widely spread. Directly a warm spell ensues they leave their shelter and begin to breed.
The numbers of the adults are kept in check by birds, lizards, dragon-flies and spiders, the latter continuing their activity among those sheltering within doors. In workshops and cellars I have seen spiders catching these mosquitoes resting on window panes.
Culex pervigilans notifies its presence by a high-pitched flying note, higher and much louder than that of A. notoscriptus. described above. Its persistent and annoying hoverings are very characteristic, and are by many regarded as more troublesome than its moderately painful bite. Graziers aver that cattle are seriously troubled at night by its attacks, and this is a matter which I hope to investigate.
Eggs and Oviposition.
Before the female of this species lays her eggs she flies around the pool or water vessel apparently looking for a suitable place; for preference she selects a floating leaf or stick. When settling, she depresses the posterior end and backs down to the water's edge. After a short time she crosses the hind legs, spreads the forelegs out sideways, lowering the body to the water level. In a few seconds the minute, perfectly white egg appears, and slides above the crossed hind legs, near the femur-tibia joints. As soon as the first egg reaches the water, others follow at intervals of about 4 seconds, and the raft begins to take shape by the female moving the point of the abdomen transversely, increasing the amount of the sweep until half the eggs are laid, then decreasing it until the last egg appears, thus forming the well-known navicular cluster with transverse rows of eggs. One raft is laid at a time, and its formation takes about 15 minutes.
The eggs of this species are laid in boat-shaped rafts, concave above, which have been ascertained to contain from 78 to 294, the average for those counted being 264. No correspondence between the type of habitat and the number of eggs in a raft has been observed. The extreme lightness of the rafts, their shape, and the surface tension of the water combine to keep them afloat in any weather, while if one purposely submerges them, the film of air caught between the tapered ends of the individual eggs quickly brings them to the surface again. The eggs are held together by a glutinous secretion which the female exudes with each egg at the time of oviposition. Each egg has a slight depression at one or both sides; this is due probably to their being pressed together while still soft, as those
I have examined before being laid are without this depression. They are laid side by side in a more or less vertical manner, the blunt end resting on the surface of the water, the pointed end being uppermost, and form rows both transversely and longitudinally, the longitudinal rows varying in number from 6 to 10. The eggs in the median rows are vertical, while the greater diameter of the lower blunt end of the individual eggs causes those of the lateral rows to tilt, so that the lower surface of the raft is wider across than the upper.
The individual eggs (Fig. 35) are cigar-shaped, i.e. thick and rounded at one end, tapering to a point at the other. They are 8 mm. long and .175 mm. across the wider end. The micropyle is at the wide end, and lies within and protected by a saucer-shaped cap. The rim of the cap is densely fringed with delicate hairs. The area around the micropyle has a reticulated appearance. In dehiscence the end of the cap falls back on a hinge (Fig. 36), the larva emerging head downwards.
When first laid the eggs are milky white, but change to a darker colour soon after exposure to the light and air, generally assuming a light brown shade; when found in situ they appear almost black, and when lifted from the water the under-surface appears silvery-white, on account of the film of air mentioned above.
The eggs are firmly held together in the raft, and I have shaken them violently in water without separating them. The rafts drift together and form stars, triangles or rows, the latter lining the water's edge like a row of canoes. They also adhere to the sides of water containers, pieces of drifting debris, blades of grass, Lemna (chickweed), Nasturtium (water-cress) and other weeds. They will withstand a considerable degree of dessication. A raft adhering to the side of a jar, from which the water had receded, was kept dry for 14 days, and on being placed in water hatched in 72 hours.
Culex pervigilans lays eggs all the year round in Auckland, and thousands of recently deposited rafts have been taken from water at 42° F. in country areas. The rafts can be found in every type of breeding place, i.e. slow-running creeks clean or dirty, drains, street gully traps, liquid manure barrels, drains around commercial premises, roof gutters, tarpaulins in railway yards, fire buckets on railway platforms, and in buildings, drinking vessels in fowl yards, stable drains, latrines, flower vases in cemeteries, pickle bottles, and tins on porches of houses, copper and wash tubs in wash-houses, old tyres, iron waggons, disused cars, conservatory water containers, flower pots in houses, and on rockeries, old boots in dumps, enemy guns in the Domain, puddles in the wheel ruts, neglected water tables, lakes, lagoons, tanks, both in the open and in the native bush. On one occasion they were obtained in brackish water with an approximate ratio of one part of fresh water to four parts of sea water, this being in a tidal mangrove swamp at Clevedon in the month of June. For preference the female will lay eggs in water rich in organic matter, but I have found them in water ranging from clean tank water to liquid manure, and again in old boilers where salammoniac had been largely used. The eggs are usually laid between the hours of midnight and daylight, the favourite hour being the one preceding day-
light; on only one occasion have I seen a mosquito depositing eggs in daylight, viz., at 7.45 a.m.
The process of hatching is sometimes a remarkable sight. On one occasion I observed the simultaneous emergence of all the larvae of one raft. First one of the caps at the lower end of the eggs fell away, followed almost immediately by nearly all the others, and for five minutes the lower surface of the raft was a struggling mass of larvae pushing downward, head first from the openings uncovered by the egg-caps. There were 256 eggs in this raft and from these 240 larvae emerged successfully, 7 failed to extricate themselves, and 9 eggs failed to open.
Larva: This larva is easily distinguished from that of the other species described by the long straight siphon (Fig. 37), most nearly resembling in this character Culex fatigans, which has a siphon relatively shorter, more tapered, and wider at the base, especially at the proximal two-thirds. The length of larvae in the fourth instar is about 8 mm. without the siphon. Greater variation is to be found
in the colouration of this larva than in the other two species described in this paper. They vary from black to brown and from green to greenish-blue; in old rusty containers they are ferruginous and in clean tank water almost white. The wriggling motion is almost straight.
The head (Fig. 38) is of a light golden colour; it is transversely elliptical, being full at the posterior margins. The front margin is slightly arcuate; a deep notch at the insertion of the antennae; maculation of the vertex is slight and is composed of small diamond-shaped spots anteriorly above the base of the antennae, and towards the centre. The mouth brushes are simple and of a golden brown colour. Pre-clypeal hairs short, stout, pointed and turned towards the middle; Pre-antennals absent. Two outer post-antennals 6 to 8 branched, spinose, reaching to proximal third of the antennae; 2 inner post-antennals 4-branched, spinose, reaching in length almost to the anterior margin. Behind the post-antennals are a pair of 4-branched spinose setae. Two pre-ocular bifid hairs equidistant between the eye and antennae. One post-ocular bifid hair. Vertical and trans-sutural hairs can best be noted by reference to the figure. Eyes large circular, usually arcuate posteriorly.
Antennae (Fig. 39) movable, often seen lying across the front of the head, darker in colour than the head, base black, slightly bent. Situated on the internal two-thirds is a bunch of 16 to 20 finely spinose hairs, in the shape of a fan in length approximately half the length of the antenna. Situated on an offset posterior to the apex are two strong hairs half the length of the narrow distal portion, on the lateral margin of the apex are two more strong hairs, longer than but otherwise similar to those just mentioned; these are movable at will; situated internally between these two sets of hairs is a short strong thick transparent spine. The surface and margins of the antennae are covered with short appressed spines, darker in colour than the antennae.
Mentum (Fig. 40) index 3.2: 2.8: pentagonal in form, 6 to 7 strongly incurved pointed teeth on each side, one large central tooth at the apex; the lower surface has a deeply arched concave depression. Mandible (Fig. 41) quadrangular, two long incurved spines below the collar on the inner margin, one short stumpy spine below these; a row of long hairs arises from the collar; four to five teeth on the process, anterior one very large, also one long pointed tooth above, a process below with moderately long hairs. Maxilla (Fig. 42) conical, divided by a wide median suture; along the suture is a series of shortened hairs; at the apex is a series of fine hairs. Inner margin carries a series of strong stiff bristles.
Thorax seen from above (Fig. 43) slightly wider than head, wider than long, divided into three angulations, with two sets of 4-branched hairs on pedunculate stems, which spring from a strong chitinous papilla, hairs black, very minutely spinose; on the anterior margin are four single, bifid, and trifid branched setae, arising from
small papillae; these hairs extend in length to beyond the anterior margin; several single and bifid hairs are to be seen on the dorsal surface. Ventral chaetotaxy can be seen by reference to Fig. 44.
On the lateral margins of the abdominal segments are a pair of bifid and trifid branched hairs on small papillae; dorsal margins of
these segments carry several single, bifid and trifid black simple hairs. Terminal segments (Fig. 45) on the eighth segment, the comb scales, 30 to 40 in number, are arranged in three irregular rows, each scale (Fig. 46) spatulate, the free margins carrying a fringe of fine hairs. Siphonal plume a tuft of six minutely pubescent hairs. Subsiphonal plume consists of a tuft of 8 to 9 pubescent hairs, much longer than the last, extending to more than half the length of the anal segment. Anal plume a tuft of 4 to 6 hairs, also pubescent, shorter than the last plume, longer than the first.
Siphon (Fig. 45) long, almost straight, slightly tapered, darker than the other terminal segments, apex darker still, arcus present. Index 5: 1. The pecten comprises a series of 8 to 10 strong and 3 to 5 smaller spines. The strong spines are equidistantly placed along the proximal third of the siphon; they are sharply pointed, arcuate
Fig. 45.—Terminal segments of C. pervigilans. larva. Fig. 46.—Comb Scale. Fig. 47.—Pecten scale from siphon.
at the base, and each bears three denticles on the basal half (Fig. 47). The 3 to 5 smaller spines are situated basad of the stronger spines, and are without denticles. Siphon plumes represented by four trifid and quadrifid branched hairs on the distal end, equidistantly spaced. Two or more small hairs on the terminal valves.
Anal segment not wholly invested with chitinous saddle, especially in the earlier instars. Ventral beard consists of 10 to 12 groups of long simple hairs. Dorsal hairs of 6 simple hairs arising from strong chitinous tubercles. Anal gills equal in length, elongated,
acutely pointed at the apex, half the length of the ventral beard, little if any tracheal ramifications. Lateral hair (Barraud) bifid and simple.
Length of pupa 5.5 to 6 mm.
Colour light to dark brown.
Surface of the breathing trumpets (Fig. 49) showing a fine diamond-patterned reticulation. Cephalothorax provided with a few dorsal hairs. Paddles (Fig. 48) ovoid in shape, hyaline, stiffened by
a mid-rib. Eighth segment carries a tuft on the lateral margin comprising 6 to 8 pubescent hairs, dorsally a single and a bifid hair. Other segments carry single, bifid, trifid and quadrifid hairs in the dorso-posterior and lateral margins.
Length of pupal life 2 to 5 days.
Larvae of Culex pervigilans can be obtained in Auckland and the surrounding districts throughout the whole year, and in every conceivable type of water container, as mentioned above in the section dealing with the eggs. They maintain themselves even in streams flowing at one and a half miles per hour, by holding on 10 stones and debris near the banks. I have also found them in wheel ruts on clay roads, although motor and horse-drawn vehicles would splash through the ruts from time to time, and close observation has shown that most of the larvae in such a wheel-rut survive the passage of a car through it. There is no water puddle so small or so foul but that these larvae can be found in it, and water-holding rubbish of any kind provides breeding places for almost incredible numbers.
The larval period of this species varies a great deal in accordance with the temperature; in the summer months it occupies from 8 to 14 days. Individuals live through the winter in either the adult or larval stage, but should a period of warm weather occur, the larvae of the fourth instar will complete their development and emerge as adults within a week. In the laboratory I have bred this species through all stages from egg to adult, although the water was never above 60° F. and often as low as 48° F., which indicates that brief spells of low temperature will not unduly retard development. I have also bred adults successfully from larvae taken from ice-covered water, and I have obtained active larvae from troughs (at Mangere) where 15° of frost were registered for three days in succession.
Experiments have shown that these larvae are capable of living in water containing a considerable salt proportion; while the sudden addition of two parts of sea-water to one of stream water will kill them at once, they will survive in water which has been brought gradually up to this salt content. They will live for several days in soft mud, rapidly regaining their activity when rain falls. At the same time they are quickly killed by oiling, with either kerosene or light lubricating oil: observations in the laboratory have shown that they die within an hour under an oil film, as might be expected. This is in marked contrast to what happens in the case of the next described species.
Finally it may be mentioned that they are far less susceptible to sound or disturbances than the larvae of Aedes notoscriptus. When I have purposely disturbed the larvae of both these species together and caused them to sink to the bottom of the pool or laboratory jar, those of C. pervigilans. have invariably been the first to rise to the surface again.
It is probably worth mentioning that of the hundreds of breeding groups I have had under observation only one failed to develop. These were kept under the same conditions as to water, food and temperature as all the others, but grew very slowly, taking a month to attain the fourth instar at which stage they remained for six months, when they died without reaching the pupal stage. This unaccountable inhibition of development is recorded in the hope that some other observer may be able to offer a comparative case, or a possible explanation.
Rachionotomyia argyropus (Walker).
Culex argyropus, Walker, List. Dipt. Brit. Mus. 1, p. 2 (1848).
Uranotaenia argyropus, Theobald, Mon. Cul. 2, p. 264 (1901).
Rachionotomyia argyropus, Edwards, Bull. Ent. Research, vol. 14, pt. 4 (1924).
General coloration of body deep black, relieved by a silvery-white scutal margin and by the white tarsi; there is also a white band at the middle of the palpi.
Female (Fig. 50): Head black, purplish in some lights. Proboscis covered with shining black scales, stout in appearance, only slightly swollen at apex; length 3.5 mm. two-thirds length of wing
and half as long as body. Labella lighter in colour, expanded, few hairs showing (in male many hairs are seen). Palpi (Fig. 51) 2-jointed, one-third length of proboscis; black scaled except for a ring of silvery-white scales in the middle; few bristles are seen.
Antennae 14-jointed, two-thirds length of proboscis, pilose (male plumose); first flagellar segment paler than the others. Ground colour dark, joint membranes lighter in colour; covered with numerous short stiff light brown hairs, long black verticillate hairs on joints; penultimate and antepenultimate joints twice the length of others. Clypeus deep brown, many black bristles projecting forward. Torus golden yellow carrying many short stiff black hairs internally situated. Eyes large, black, with a coppery sheen. Frons filled up by a dividing black line. Nape and occiput black scaled. Above the nape and below the eyes is a circular fringe of flat pastel-blue scales. On the lower part of the fringe is a border of strong black bristles projecting forward. On the nape are several upright black scales.
Thorax ferruginous anteriorly, becoming much darker on the mesonotum on account of a covering of short narrow curved black scales; some light golden bristles also present are too scattered to affect the general coloration. Prothoracic lobes yellow, with several strong dark bristles; scutellum ochraceous, trilobed, with several golden bristles projecting backwards and partly covering the metanotum. Metanotum black.
Pleura yellow, with a silvery-white stripe across it. Pleural pilotaxy (Fig. 52): The protergum is light golden in colour, carrying
6 to 8 light-coloured pronotal bristles, and two black ones. The pro-episternum is same colour, with 6 to 8 prosternal bristles. Pro-epimeron with 2 to 4 pro-epimeral bristles arranged on the posterior margin, protecting the first spiracle. The spiracular area has no
bristles to cover the first spiracle, this function being performed by the pro-epimeral chetae in this species; it has two posterior bristles on the apex. The mesepisternum has from 3 to 7 pre-alar but no sternopleural bristles. The mesepimeron has 10 to 12 upper mes-epimeral bristles arranged to cover the second spiracle; lower mesepimeral bristles are wanting. A broad stripe of silvery-white imbricating scales passes across the lower part of the mesepimeron and on to the pro-episternum; there is another broad stripe on the margin of the mesonotum.
Wing (Fig. 53): Length 4 mm., longer than proboscis, and reaching beyond the last abdominal segment. Fork cells long and nar-
row, Cell R.2 slightly longer and narrower than Cell M.2 their bases not quite opposite, that of the former being more proximal; stem of R.2 shorter than that of M.2, and rather more than one-third length of its cell; stem of M.2 more than twice length of its stem. Supernumerary
Fig. 53.—Wing of Rachionotomyia argyropus.
Fig. 54.—Median scale.
Fig. 55.—Lateral scales.
Fig. 56.—Fringe scale.
and mid cross veins opposite; posterior cross vein three times its own length distant from mid cross vein. Median scales (Fig. 54) very broad and short; lateral scales (Fig. 55) longer, narrower and curved; fringe scales (Fig. 56) long and tapered. Haltere with pale yellow stems, knobs with bluish-grey scales.
Legs brownish-black, distal ends of each segment darker than proximal. Coxa and trochanta yellow. Fore-leg: Femur black at base, changing to dark brown distally except for a patch of white scales on the apical four-fifths; apex, or knee joint white. Tibia dark
brown, almost blue black in some lights; apex and knee joint with faint bluish-white scales. Tarsus: The fourth segment and part of the third are white; the fifth is black except for a few white scales on the ventral surface which gives it a dull sheen. Mid-leg: Femur as in fore-leg. Tibia also as in fore tibia except that it lacks the apical scales. Fourth and fifth tarsal segments chalky white. Hind-leg: Femur with distinct white patch at apical four-fifths, apex and knee joint white. Tibia with white patches at apex and knee joint. Apex of third, all of fourth and of fifth tarsal segments white; total length of tarsus half as long again as tibia. Ungues small, simple, curved, black; of fore- and mid-leg curved, simple black; of hind-leg smaller, almost straight and black.
Abdomen covered with flat fuscous scales, the testaceous ground colour showing through where the dark scales have become lost; anterior portions of each segment yellow, their posterior borders carrying a number of golden hairs; each segment with silvery-white lateral apical scales. On the ventral surface the segments are white-scaled apically. Posterior segment short and strongly bristled.
Total length 7 to 7.5 mm.
Male: Palpi as in female. Ungues of fore- (Fig. 57) and mid-leg curved, black; of hind-leg smaller, almost straight, also black. A feathery appendage springs from the base of the unguis, and two strong slightly curved and tapered spines arise from the dorsal portion of the distal end of the fifth tarsal joint.
Hypopygium (Fig. 58) with short oval basal lobes, heavily bristled throughout; claspers long, narrow and gradually tapering to an acute point. The harpago area and the phallosome together are
cone-shaped and very bristly; arising from the harpago are two triangular appendages; above these are two other narrow curved appendages turned ventrally.
Habitat: New Zealand only (Walker), Nelson (Gourlay), Wellington (Hudson), Ohakune (T. R. Harris), Mahia Pen. (Miss Castles) and Waitakere Ranges, Auckland (D.H.G.).
The large size, the conspicuous white-tipped tarsi and the white ring on the palpi of this species at once serve to distinguish it from others. It has also a peculiar flight, spreading its legs outwards and upwards. When resting it lifts the hind-legs upwards and bends them forward past the head and back again.
I have found it only in the native bush, and have never observed such a swarm as that recorded, from a description given by Mr. W. W. Smith, by Theobald (Mono. Culic. of the World, vol. 2, p. 265). In this case it is stated that a train “passed through a wall of them, three quarters of a mile long, twenty feet high, and eighteen inches thick.” I am not sure, however, if Mr. Smith was right in his identification of the species, for no one could identify it from Walker's description, which gives no idea of its appearance.
I have frequently found specimens resting on tree-trunks, and under the eaves of huts in the bush. They also hibernate both under dead nikau and tree-fern leaves still hanging to the trees, and in the now numerous week-end cottages in the Waitakere Ranges. The owners of these cottages find, whenever they light a fire after a short absence, either in summer or winter, that numbers of this mosquito are disturbed from curtains, drapings and corners where they have been sheltering.
They are persistent biters, attacking directly and fairly quietly but not so silently as Aedes notoscriptus. Their bites, too, are certainly more painful than those of A. notoscriptus or C. pervigilans, and people who are apparently immune from the latter two species are attacked by R. argyropus.
I have kept both males and females in observation cages, but not for longer than 8 weeks, and only once obtained eggs laid in the cages; these, however, developed successfully.
Edwards (1924, p. 360) suggests that this may be the species described by Miller (1920, p. 36) as breeding in epiphytic Astelias; but Miller stated definitely that the species described as so breeding by him was Aedes notoscriptus. Moreover, the unusual larval habits to be described below also render it most unlikely that it would breed among leaf bases.
Oviposition and Eggs.
Oviposition: The female of this species deposits her eggs in daylight, differing in this respect from C. pervigilans and (probably) A. notoscriptus. She begins by standing on the surface of the water, and not on the edge or sides of the container or on floating leaves and debris, as with Culex pervigilans. Once she has settled on the water, she begins by moving her hind legs apart, spreading them out in the necessary position for oviposition, but not crossed as in C. pervigilans. After a short space of time (usually two or three
minutes) she begins to deposit her eggs regularly, one every few minutes, until there are from twelve to twenty laid, when she rests awhile, brings her legs back to normal posture and flies away. The eggs when first laid are very light in colour but do not glitter as they do when a few hours old. The female prefers a shaded part of the tank in which to deposit her eggs, as for instance under a piece of asbestos partly covering a tank I was observing, away from wind and sunlight. If there is no wind to disturb the water, the eggs will remain in their little clusters of twelve to twenty, but do not adhere to each other by any glutinous substance as in Culex species, but simply by surface tension. The writer has on many occasions observed females depositing their batches of eggs, which can be discerned with the naked eye once one knows what to look for, the whole cluster not covering more than the space of a shilling piece.
I have had tanks where this species has been breeding during the past ten months under close observation both during the night as well as the day, spending many hours in so doing; but in no instance have I found eggs being deposited during the hours of darkness; in fact, when I have gone to the tank after 5 p.m. or after dusk, no mosquitoes could be seen. On the other hand, from the last week in October until the last week in May, I have on numerous occasions seen females depositing eggs in daylight, especially from noon until just before dusk, after which they flew away. The females begin to oviposit in October and continue to May, more eggs being seen on the water during April than in any other month.
They do not seem to be so easily disturbed as the females of other species, for on many occasions I have lifted the lid of the tank (i.e., a piece of asbestos covering two-thirds of the top) to take observations of either the larvae or adults, and they were in no way per turbed, but continued ovipositing apparently quite oblivious of my presence, this being directly opposite to C. pervigilans or A. notoscriptus.
On one occasion while I was observing females ovipositing (some short time before dusk in the month of April) one flew up from the water and alighted on my hand and, after a little wandering about, began to insert her lancets into my skin. This is the first occasion on which I have been aware of being bitten by a mosquito. She began to suck blood, continuing for exactly two minutes; almost immediately two more females arose and alighted on my bare arm and also began to suck blood, the time being two minutes and two minutes and five seconds respectively. While the lancets were inserted the hind legs were performing peculiar movements, being lifted up in the air and turned about in a rotary motion and down again.
Rachionotomyia argyropus seems to prefer tanks in secluded localities surrounded by native bush and partly covered for oviposition. I have in mind two tanks in the bush at Titirangi, one almost wholly covered by a piece of asbestos and shaded by ponga and native trees, the other more open and exposed to wind; these tanks are not more than sixty yards apart. The secluded and almost covered one has an abundant supply of eggs during the months mentioned above, while the wind-swept one has only odd eggs, and no females have been observed on the water. I have frequently found this species
breeding in galvanised iron tanks but not in the several square ungalvanised ones to be found in the district, and twice only in barrels. In every case their presence seemed to be conditioned by the shelter of native bush, for I have examined many galvanised iron tanks not far from native bush, and surrounded by exotic trees, without finding signs of the species, although they were breeding freely in tanks sheltered by native bush not more than a hundred yards away. This preference for a shaded tank situated among native bush is rather puzzling, for I have carefully searched pools, streams, rot- and knot-holes in trees in the heart of the bush, such as one might expect to be the natural habitat, without finding any signs of the breeding of this species. I have placed tins of water containing dead leaves round about these tanks in various heights and positions with and without a covering over them, and even placed one on the piece of asbestos which partly covers the tank mentioned above, trying to induce the female to deposit her eggs therein, but with no avail. On the other hand, eggs have been found in shallow dishes of water in the observation cage at the Museum where I have kept adults of this species during the month of April.
Fig. 59.—Dorsal view of egg of R. argyropus.
Fig. 60.—Lateral view of egg.
Fig. 61.—Showing dehiscence of egg.
Eggs: The eggs of this species are quite different from those of the other New Zealand species, i.e., Culex pervigilans and Aedes (Finlaya) notoscriptus, not only in form and structure, but also in colour and dehiscence. Seen in the ventral and dorsal view (Fig. 59) the egg is elliptical, the ends being rather pointed, but not acutely. Seen laterally (Fig. 60) the lower edge is only slightly convex, the upper considerably so, thus giving a dome-shaped appearance.
|Length of egg||.025 inches.|
|Greatest height||.012 inches.|
|Greatest depth||.01 inches.|
When seen on the surface of the water, these eggs appear to the naked eye to be of a greyish-blue colour, and when the sun shines on them at certain angles they give the appearance of floating diamonds, in other lights they look like tiny bubbles. Under a low power microscope (twelve diameters) they are found to be lavender-coloured. This lavender coloration is really due to the film-like roughened covering forming an air sac round each egg; this acts as a float to the individual eggs. When the eggs are numerous they give a frosted appearance to the surface of the water. When the epidermis is lost through agitation of the water, the eggs assume a brownish hue and sink to the bottom, but this does not interfere with their successful hatching. On the surface of the water of the tanks, sheltered from all winds,
frost-like clusters can be seen scattered about, but a very slight wind causes the eggs to skip about over the surface; again, when endeavouring to pick them up I find they skip away, and it is very difficult to secure them. The only successful method the writer has found for collecting them (and this needs careful manipulation) is partly to submerge one end of a wooden match in the water at an angle of 45°, working the submerged part under the egg and drawing the match up with the egg adhering to the rough and wet surface; one has to be very gentle, and to see that the match is wet, for the slightest jar will send the egg skidding away. When the eggs are floating about and come to within about a quarter of an inch of one another they immediately run together and form scum-like masses like those of aquatic Collembola leaves.
In dehiscence (Fig. 61) a split runs full length along the lateral margin. The eggs usually take from two to three days to hatch with the water at 60° F.
Larva: The larva of R. argyropus can be easily distinguished from that of other New Zealand species by the coloration of the segments, the four posterior ones being of a bright golden yellow colour while the anterior ones are pure white, both colours being due to the presence of fat globules. The siphon has five simple pecten spines, while the anal gills are long and broad with a decided tracheal ramification which makes it conspicuously different from any other species in the same container.
Head (Fig. 62) strongly chitinised, almost circular, slightly broader than long. Front margin slightly rounded; a notch at the insertion of the antennae. Pre-clypeal hairs short, close to the centre
and turned inwards, almost touching across. Pre-antennals absent. Outer anterior hairs consist of three 4- to 6-branched setae each on a short stem; these hairs, which are simple, extend to half the length of the antennae. Midway between the antennae and the eye on each side is a quadruple tuft on a pedunculate stem. A single simple anterior-ocular bristle stands immediately above the eye.
Antennae (Fig. 63) jointed, movable, straight or slightly tapered. Antennal tuft consists of two bristles situated at the apical two-thirds and extends a distance half way to the apex. Terminal-antennal hairs two long and two shorter hairs.
Mouth brushes of a deep golden brown, simple not bushy. The mandible (Fig. 64) is quadrangular, one long recurved elongated spine on the outer ridge, one short stumpy spine immediately below; premandible has one strong tooth and three minor ones below; there is a series of strong recurved spines along the outer ridge or margin. Maxilla (Fig. 65) roughly sub-ovate with conical apex invested with a number of long hairs; four spines on the margin. Palpus quite rudimentary, terminated by four short hairs on a stout spine-like protuberance on the inner margin. Mentum (Fig. 66) triangular, index 4.8: 3.4, one large tooth in centre, 13 strongly curved and pointed teeth on the left, 12 on the right, lower margin crenulated.
Thorax from above (Fig. 67) cuneiform, slightly wider than head. On the latero-dorsal margin are three groups of setae borne on distinct golden-tipped papillae; on the dorsal surface more tufts are to be seen; all hairs finely pubescent. For vestiture of ventral surface see Fig. 68.
Abdominal segments with bifid hairs on lateral margins and short minute hairs on each side of them. Lateral comb of eighth segment (Fig. 69) in the form of a semi-lunar patch of 100 to 140 spines, the posterior ones being more spatulate, carrying a fringe on the widest end of the free margin (Fig. 70). The anterior spines are shorter. Adjacent to the lateral comb is a tuft of palmate setae comprising 12 to 16 black hairs which show up conspicuously on the yellow segment. Siphonal plume a tuft of 6 to 8 pubescent hairs on a short stem, reaching to half the length of the anal segment. Sub-siphonal plume one bifid tuft slightly longer than the anal plume. Anal plume a single bifid tuft. It will be noticed by a comparison of Figure 69 with Figs. 20 (p. 213) and 40 (p. 224) that the anal gills of the larva of R. argyropus are 2 ½ to 3 times longer, and correspondingly broader than those of the larvae of A. notoscriptus and C. pervigilans; moreover, in R. argyropus they have a very pronounced tracheal ramification (Fig. 72), which is barely discernible in the others. Obviously they are more strongly functional as respiratory organs in R. argyropus, and this no doubt explains the ability, to be referred to below, of this larva to remain below water for practically indefinite periods.
Siphon: Index 3: 1, strongly tapering after two-thirds, widest just beyond base. Pecten comb comprises five apparently simple spines, each one being larger and further apart proceeding apically, under a high power they appear finely serrated on the outer edge (Fig. 71). Terminal hairs consist of two delicate cirri, as long as, or longer than, the width of the apex; these are situated one-third
of the distance in from the edge, are movable and are more often turned outwards, sometimes in a complete circle, giving a hooked appearance; at each expansion and contraction of the tracheal system they diverge in response. Two strong hairs on the margin also partly hooked. A double row of bifid hairs on each side of the siphon, nine one side and ten the other; these are simple, line of demarcation
Fig. 69.—Terminal segments of R. argyropus.
Fig. 70.—Lateral comb spine from 8th segment.
Fig. 71.—Pecten spine.
Fig. 72.—Anal gill of R. argyropus.
begins a short distance from the base; union of the stem to the siphon is in the form of a small papilla. Arcus absent. Anal saddle not completely invested, chitinous. Dorsal beard arranged in three groups of 5 to 6 pubescent hairs in each. Ventral hairs, one single and one bifid, simple. Anal gills (Fig. 72) as long as or slightly longer than ventral beard, asciform, with a highly evolved tracheal ramification. Lateral hair is one strong bifid hair.
Larval stage takes 21 to 28 days.
Adults of this species have been taken in Wellington (Hudson), Ohakune (Harris), and Nelson (Gourlay), but the eggs and the interesting larvae have hitherto not been identified. Invariably the larva of R. argyropus has been found in tanks in or near native bush. In the Auckland district the species is confined to a stretch of bush beginning at Titirangi, continuing on to Huia in a westerly direction up the coast to Kare Kare, thence to Muriwai and back in a straight line to Nihotupu and Oratia. The first discovery of this larva was made by Miss Zoe Lloyd, who found them in water when drawing it off for household use. When Miss Lloyd brought them to the Museum it was at once seen that they were different from any hitherto examined. On visiting this tank and looking in from the top, I could see no larvae and concluded that the coating of oil applied to the surface by Miss Lloyd had killed the larvae and pupae in the usual way. However, on drawing off some water from the tap I was surprised to find that they had apparently suffered no ill effects, for numbers kept flowing out of the tap. This was my first intimation that they were able to derive the greater part of their oxygen from the water.
The writer has approached this tank in a most cautious manner, not once but many times, and found it was the exception and not the rule to find any larvae near the surface. In their natural resting or feeding posture in this tank they keep well down near the bottom. They assume varying positions, vertical or horizontal, and after a period of time in one position they give a kick and a twist and assume another, and so on. Their movements are stiff and decidedly jerky or abrupt. It is not till there is some disturbance, such as the stirring of the water or shaking the tank, that these larvae come to the surface, and then only in an aimless fashion, zigzagging backwards and forwards; and in many instances the writer has seen them come to within ten inches or so of the surface, remain suspended for a while, and then quietly sink down again, just as though they had come up to see what had caused the disturbance. Again, I have seen them rise to the surface keeping the body vertical, no movement of the abdominal segments being perceptible.
To obtain specimens of larva and pupa the writer always let the water run through a strainer under the tap, surface-sweeping being of no use. It is curious that I have never been able to find first and second instars in the natural field habitats, although, of course, these stages normally appear in cultures bred in the laboratory. It is possible that they live in the middle depths of the tanks, and in the coming summer I intend to test this. In containers at the laboratory they spend a good deal of time lying in a horizontal position without any flexing of the segments, and progress along the bottom by the vibratory movements of the mouth brushes, occasionally deviating from this course by a simple fleck of the tail, and then proceeding as before. Another habit of the larvae is to hide or remain under the leaves and debris at the bottom of the vessel. When they hang from the surface of the water they suspend themselves in an almost vertical position, the first three segments being slightly bent. When they sink to the bottom they remain on their head for some time, then gradually fall over with the ventral surface uppermost. While in this
position they rapidly protrude and retract their mouth brushes, causing bright scintillations of reflected light as if they were luminous.
In laboratory jars, without leaves, these larvae spend more time at the surface than they do in large tanks with leaves and other debris at the bottom, probably on account of there being insufficient oxygen in the small amount of water. I have placed larvae of this species together with those of Culex pervigilans and Aedes (Finlaya) notoscriptus in a gallon jar with decaying leaves, and observed that while the latter spent nine-tenths of the time at the surface Rachionotomyia argyropus spent the same amount of time under the leaves.
The larvae of R. argyropus were placed in a 4 oz. corked bottle, two-thirds full of water, and posted from Auckland to Nelson, being over a week on the journey. On the return journey to Auckland the bottle was not opened for 14 days, yet not one death took place. The result is quite contrary to the usual experience in transporting mosquito larvae, for even a day's journey in a jar without the cork being removed is nearly always fatal to those of the other species. In some experiments which the writer conducted during the winter at the Museum several larvae were placed in a large jar of water and heavy lubricating oil was poured on the surface, making a perfect film or layer ¼ inch thick: no leaves or food material were provided. The first larva died on the 17th day, 3 had died within a month, and the remaining 8 lived till the 36th day, and, judging by the shrinking of the fat body, their death was as likely due to starvation as suffocation. The larvae occasionally did make an attempt to come to the surface, and clung for a short period to the under-surface of the oil layer. On descending they were seen vigorously cleaning the siphon with the mouth brushes.
Extended experiments will be conducted shortly to see how long they will survive in similar vessels but with an abundant supply of leaves.
Some larvae of this species in a barrel at Titirangi have been kept under observation for several weeks and were seen to be holding on to the sides of the barrel by the terminal hairs of the siphon, assuming a vertical position. Alternatively they assumed a horizontal position, holding either by the head or the siphon and remaining there till disturbed. They have also been observed crawling up the sides of the barrel from one position to another, using the hooked hairs on the apex of the siphon for pulling themselves along. In these last two observations it was noticed that the larvae remained in this position at a distance of ten to twelve inches below the surface down to the same distance from the base of the barrel. When disturbed they sank to the bottom, remained there about five minutes and when all was quiet again began to adhere to the sides near the bottom, and gradually to work their way upwards in short stages till they came to within ten to twelve inches below the surface as before.
In a number of experiments carried out at this barrel the writer found that the larvae would congregate only under the portion which chanced to be shaded, i.e., by a board, and when this board was moved to another part of the top the larvae then moved to that part now shaded. In the iron tanks, where this species has been found, no instances of their adhering to the sides have been observed.
Another instance of their seeking the shade was noted when several were placed in a petrol tin containing water with abundant leaves at the bottom; very soon after they had been placed in the water they disappeared, having all hidden under the leaves. A still more striking instance was seen when all the boards were removed from the top of the barrel mentioned above; the only shade left was that afforded by the two down-pipes, which very limited space was crowded by larvae jostling one another for a place in the shade. The area thus occupied tapered down from the object causing the shade, i.e., it was the shape of the shadow cast.
It will be seen that this larva differs from the others described here, if not from any mosquito larva hitherto described, in its ability to remain below the surface of the water indefinitely; and that it has corresponding structural modifications in the large size of the anal gills and their tracheal ramifications. Another unusual feature is the large size of the terminal siphonal hairs, which seems to be associated with their habit of adhering by the siphon to the side of a barrel.
As the breeding stages of this mosquito have up to the present been found only in rain water tanks and barrels, its natural breeding place has yet to be found. As mentioned above (p. 234) many varied situations have been searched without success, but it may be that the peculiar characters mentioned above and the most unusual, if not unique, manner of breathing may provide a clue to the natural breeding places of this interesting mosquito.
This pupa has a definite colour pattern. The cephalo-thorax is dark, as also are the abdominal segments, but the intersegmental membranes are almost white. When the pupa is in motion with the abdominal segments contracting and expanding the white intersegmental membranes give the pupae a sparkling appearance as if air-bubbles were collecting on them. The pupae on first emerging from the larval stage are quite white except for the eyes, but gradually grow darker in colour as the pupal life proceeds. The breathing trumpet (Fig. 73) is large and square shaped. The cephalo-thorax is jet black in colour, abdominal segments lighter with patches of dark coloration on the median portion of the dorsal and ventral regions and a lighter coloration on the intersegmental membranes. Each dorso-lateral margin of the last two segments (Fig. 74) is provided with a bunch of setae comprising from twelve to sixteen finely pubescent hairs on a short pedunculate stem, these are highly irridescent under certain lights. On the latero-dorsal margins of the other segments are two long single hairs extending past the next posterior segment; several minute bifid and single hairs are to be seen on all segments. Caudal fins (Fig. 74) mitre-shaped, hyaline and stiffened by a strong midrib of a golden colour, no terminal hairs.
The pupa of this species is not able to obtain air below the surface for so long a period as the larva; nevertheless it is capable of remaining there for a longer period than the pupae of other species. In the barrel mentioned above the writer noticed several pupae holding on to the sides of the barrel. They would hold on for a short time, then ascend to the surface for air, and after a few minutes would descend about six or seven inches, move to the side of the barrel, turn sideways on to it, and gradually turn over with the dorsal region turned towards the barrel, and, so far as the writer
could see, adhere with a pair of seta-clusters found on the first segment just below the cephalo-thorax. This cluster comprises twenty or more hairs arranged fanwise on a short peduncle. This extraordinary posture placed them in a horizontal position, head and caudal fins projecting. These movements were repeated all the time the observation took place, and were always concluded by the resumption of this curious attitude.
During the last day of pupal life, the whole of the arrangements of the hypopygium and scales can be discerned (Fig. 75).
Length of pupal life, 6 to 8 days in summer.
This pupa, with its decided coloration, is very easily distinguished from that of the other New Zealand species, the cephalo-thorax and the abdominal segments, both dorsally and ventrally, being dark, and the intersegmental membranes lighter. When the pupa is in motion the muscular expansion and contraction of the posterior segments imparts a pronounced mottled and sparkling appearance as though there might be air bubbles on the intersegments.
Keys To Species Described.
|1. Proboscis with a distinct white band||Aedes notoscriptus|
|Proboscis uniformly dark||2|
|2. Thorax uniformly dark, tarsi almost wholly white||Rachionotomyia argyropus|
|Thorax with light coloured bands, legs including tarsi black||Culex pervigilans|
|1. Eggs in rafts, individual eggs cigar-shaped||Culex pervigilans|
|Eggs not in rafts||2|
|2. Eggs single or in star-shaped masses, elongate oval and pointed at both sides||Aedes notoscriptus|
|Eggs single or in scum-like masses, short oval with blunt ends||Rachionotomyia argyropus|
|1. Siphon not more than twice as long as broad; a single siphonal tuft at end of pecten||Aedes notoscriptus|
|Siphon three or more times as long as broad; more than one siphonal tuft||2|
|2. Pecten spines each with 3 basal denticles (Fig. 47)||Culex pervigilans|
|Pecten spines simple, without denticles (Fig. 72)||Rachionotomyia argyropus|
|1. Paddles with terminal hairs||Aedes notoscriptus|
|Paddles without terminal hairs||2|
|2. Paddles mitre-shaped||Rachionotomyia argyropus|
|Paddle ovoid||Culex pervigilans|
In conclusion I wish to express my thanks to the Chairman (Professor Thomas), the Hon. Secretary (Mr. F. L. Armitage) and members of the Mosquito Control Committee for their help in many directions in connection with this work, and also to Mr. Gilbert Archey, under whose personal direction and tuition the studies have been undertaken, and who kindly placed the facilities of the Auckland Museum at my disposal. I also desire to thank Dr. David Miller
and Mr. A. Tonnoir for help, instruction and advice kindly given me during three weeks' study carried out at the Cawthron Institute.
Finally, I have to thank friends and helpers throughout the country, many whose names even are unknown to me, for their courtesy, help, directions and interest during my field studies, and for their invariably offered hospitality; among them I should like specially to mention Mr. W. Hawke, of the Auckland Museum staff, who very kindly acted in many capacities on behalf of the research during my several absences.
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Cooling, L. E. Larval stages and biology of the commoner species of Australian mosquitoes. Service Pub. (Trop. Div.), No. 8, pp. 21–23. (1924).
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Edwards, F. W. A Synopsis of the adult mosquitoes of the Australasian region., pp. 360, 382, 396. Bull. Ent. Res., vol. 14, pt. 4 (1924).
Miller, D. Report on mosquito investigation in North Auckland province. N.Z. Dept. of Health Bull., No. 3 (1920), p. 1.
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