Mosquito Life in the Auckland District.
Report Of The Auckland Mosquito Research Committee On An Investigation Made
[Manuscript received by the Editor, July 15, 1935; issued separately, September, 1939.]
This report presents the results of an investigation into the Mosquito life of the Auckland district.
The research was originally started by Dr. David Miller in 1918, but his many duties prevented him carrying the work to a conclusion.
The Auckland Mosquito Research Committee was formed to organize and carry out the work and Mr. D. H. Graham was appointed Research Officer. The immediate objects of the research were:—
(1) The determination of the species of mosquito present in the district.
(2) Their seasonal and geographical distribution.
(3) The conditions affecting their life.
(4) Possible measures of control.
The investigation extended over a period of three years, from Mercer in the south to Kaitaia and Spirits Bay in the north. The research was carried out by Mr. David H. Graham, and comprised systematic study (Graham, Trans. N.Z. Inst., vol. 60, pp. 205–244, 1929), field work, experimental breeding and culture of mosquitoes, and other laboratory work carried out at the Auckland Museum, where accommodation was provided by the Council.
The study was under the supervision of Mr. Gilbert Archey, Director of the Museum, a member of the Committee.
The expense was borne by grants from the New Zealand Institute and the New Zealand Government Departments of Health and of Scientific and Industrial Research.
The Committee has to express thanks and appreciation to the officers of the Forestry Department and to the Sanitary Inspectors for their willing co-operation and assistance, particularly to the late Mr. C. Weaver for his assistance in examining overseas vessels.
The results of the work are of importance in two respects. We now possess a detailed knowledge of the life history of the mosquitoes of the northern part of New Zealand. Further, the report furnishes a basis for the action of Health Authorities in the suppression of a pest to human beings and stock, and assistance in combating the danger of the introduction of disease-bearing mosquitoes from overseas.
On these grounds the Committee feels that the research has been, amply justified.
A. P. W. Thomas,Chairman.
Culex pervigilans Bergroth.
1889.Wiener entom. Zeitung, p. 295.
This, the commonest New Zealand species, is endemic and occurs throughout the country, but is most abundant near habitations. It is a nocturnal biter and hovers for a long time before biting, emitting a high, loud, singing note much louder than any other species. Its bite, however, is generally much less severe than that of other species.
It is distributed throughout New Zealand, and in Auckland breeds at all seasons, even during the short warm periods which occur during winter. It is almost unrestricted in its choice of breeding-place, in which it differs from all other New Zealand species. It breeds in practically every place in which water can collect and remain unevaporated for even a short time.
Adult females usually retreat to the shelter of buildings, especially of cellars or unfrequented darkened rooms, between May and August; nevertheless egg-laying adults have been found in the city and suburbs all through the winter.
The larvae of C. pervigilans are able to “carry over” during the winter in quite exposed situations, and have been observed actively swimming under ice, coming up to breathe at the air spaces which often form. In fact, the distribution of C. pervigilans in the Auckland district seems to be restricted more by higher temperatures than by lower, for as we go north it is increasingly replaced by Taeniorhynchus iracundus, being completely supplanted in pools with a temperature of over 70° F.
Culex fatigans Wiedermann.
1828. Aussereurop. Zweifl. Insekt., I, p. 10.
A species of world-wide distribution occurring in New Zealand only in and about Auckland City and Whangarei and therefore believed to be introduced. Bites at night and breeds through the year in any place exposed to full sunlight and holding water charged with decaying organic matter.
As with C. pervigilans, adults of C. fatigans have been found breeding and biting all through the winter, and the larvae have been observed to continue their development, even to pupating and emerging as adults in June. Curiously, however, adults could never be found in early spring (September and October) and it would seem that the months of July and August are cold enough to kill them off and that the species survives from year to year through the hibernating larvae.
Culex annulirostris Skuse.
1888. Proc. Linn. Soc. N.S.W. (2), iii, p. 1737.
An East Indian and Western Pacific species discovered (May, 1929) breeding in the hold of s.s. Tofua on arrival at Auckland from Suva, live larvae being subsequently discovered in a barrel on the waterfront. It is hoped that the destruction of this brood has prevented the establishment of the mosquito in New Zealand.
Taeniorhynchus iracundus (Walker).
1848. List Diptera Brit. Mus. (1), 6.
An endemic species found only in Auckland Province in scrub and bush areas. It is a persistent night-biter and is especially-troublesome around farms, where it pesters the stock. Breeding has been observed from December to May, but hibernating females have been seen sheltering under fern and nikau leaves: the males probably die off after fertilizing the autumn brood of females.
It does not begin to lay eggs until the water is about 65° P. The eggs so laid, however, will continue to develop when the temperature drops to 60° F., but development is suspended below that. This species favours water of a higher temperature than the other New-Zealand species. At Spirits Bay larvae were abundant in pools in sunny sheltered creek-beds with a temperature of 85° F., and heavily charged with strong-smelling decaying vegetation. In summer these pools became too hot and putrid for the welfare of the “native trout” (Galaxias fasciatus), which died after endeavouring to escape by jumping out of the water.
Taeniorhynchus tenuipalpis Edwards.
1924. Bull. Ent. Research, 14, p. 366.
An endemic species confined to scrub and bush areas of the Auckland Province, where it annoys bush campers at night. Beyond two records of egg-laying, Waimauku (January) and Piha (May) no information is available as to its breeding.
Aedes notoscriptus Skuse.
1888. Proc. Linn. Soc. N.S.W. (2), 3, p. 1738.
An East Indian, West Pacific and Australian species, occurring-in New Zealand only around Auckland city, Nelson city, and Whangarei. On this account and because of its having been more than once taken alive on vessels on their arrival at Auckland from Sydney, this mosquito is believed to be a recent introduction. It is essentially a day-time biter. It breeds during the summer and only in the shade of trees or buildings, though hibernating adults may emerge and commence biting during a warm spell in the winter.
Gullies in Auckland, where all too frequently numbers of tins have accumulated among the scrub, are typical of its habitat. It has been found in shaded drains, catch-pits and waterholes, but it is usually restricted to leaf bases and holes in trees, and well-sheltered artificial containers on the ground.
It hibernates in both adult and larval stages, the former resting under tree-fern fronds from May to October, with occasional brief flights in any spell of unusually warm weather. Normally no adults emerge from the pupae from June to October, but some were once observed to emerge in September in exceptionally well sheltered warm situations in the Waitakere Hills, and once in the Grafton Gully in Auckland.
Aedes antipodeus (Edwards).
1924. Bull. Ent. Res., 10, p. 132.
An endemic species restricted to dense forest in Auckland Province. Adults are active throughout the year and bite at any time
of the day or night. The eggs are apparently not laid in water, but are deposited on slime or mud. Females have been observed laying eggs on damp mud in winter. If rain falls on such mud, development at once commences and continues to the pupal stage even though the temperature of the water be no higher than 42° F. The whole development has been completed in three weeks in water at 52° F. Larvae have been raised from both damp and dried mud; and dry pools from around which adults have been absent for a considerable period have been observed to abound with larvae within 24 hours after a fall of rain. This habit of “carrying over” a dry spell in the egg stage enables it to meet the uncertainty of an irregular and intermittent rainfall.
The lower temperatures at which this species continues its development may be associated with its more southern distribution, and also with the greater elevation at which it usually occurs.
Aedes vexans Meigen.
1820. Syst. Beschr. Eur. Zweifl. Ins., vol. 6, p. 241.
An East Indian, Western Pacific and Australian coastal species. The only record of it in New Zealand is that of larvae found in a tin of water jammed among rocks just above high tide at Russell in July, 1929.
Rachionotomyia argyropus (Walker).
1848. List Dipt. Brit. Mus., 1, p. 2.
An endemic species recorded from Nelson, Wellington, Ohakune and Waitakere Hills. It seems definitely to be restricted to the native bush, but the tanks and barrels around bush cottages, in which alone it has been found breeding, can hardly be part of its native habitat, and its true native breeding place has yet to be discovered.
Apparently it breeds, and its larvae continue to develop, from November to May, the development being, however, suspended from June to October, when the adults also are completely quiescent, sheltering under the eaves of cottages, outhouses and sheds in the Waitakere Hills. Its larvae possess large anal gills plentifully supplied with tracheae which enable it to remain below the surface. This suggests that deeper pools or slow-moving streams may be the normal native breeding places. It is a night-biting species.
Opifex fuscus Hutton.
1902. Trans. N.Z. Inst., vol. 34, p. 188.
An endemic species restricted to rocky parts of the coast and breeding in semi-saline pools just above high water and frequently splashed by the spray. The larvae are able to remain below the surface for unusually long periods. A night-biting species.
Anopheles maculipennis Meigen.
1818. Syst. Beschr. Zweifl. Ins., vol. 1, p. 11.
Recorded here because a live female of this transmitter of malaria was taken at Auckland on a ship from the East Indies on May 27, 1929, and another on September 4, 1929, on a ship from Samarang.
|Mosquito.||Source.||Habitat.||Breeding Period in New Zealand.||Bite.|
|C. pervigilans||Endemic||City and suburban||All seasons||Night|
|Aedes notoscriputs||"||"||Summer only||Day|
|A. antipodeus||Endemic||Country and bush.||All seasons in wet weather||Day and night|
|Culex annulirostris||Pacific Introduced, but not established||Unknown||Night Day and night|
|Anopheles maculipennis||On ships only at Auckland|
Effects Of Salinity.
Experiments with larvae of C. pervigilans showed that while the sudden addition of twice the volume of sea-water to a given quantity of fresh water killed all larvae within 48 hours, they would survive in water brought gradually up to this salt content. Gradual addition of the sea-water produced no effect till the added sea-water exceeded the fresh, but most larvae survived until after the mixture had become more than two of sea-water to one of fresh.
Of greater interest was the effect of salinity on the pupae. When the added sea-water was double that of the fresh, the maturity of the pupae was hastened, and all hatched out almost immediately. For example, in one experiment with 70 larvae and 50 pupae, while all the larvae died within 24 hours, all the pupae changed to adults in the same period. The pupae in control jars, however, kept in similar conditions of light and temperature, changed to adults at the rate of one or two per day, as normally happens in winter, during which this experiment was made.
Apparently the increase in salt-content caused the acceleration of the change from pupa to adult, and this suggests in the drying of a pool containing mosquito pupae, the increase in the percentage of salts thus brought about is one of the factors in hastening the change to the adult condition, another factor being the increased rise in water temperature of a pool exposed to sun. The advantage to the mosquito of hastened development in a drying pool is obvious, and such accelerated development was frequently observed in the field.
(Mosquito life in drying pools.)
Experiments with larvae and pupae of C. pervigilans showed that they were able to survive for over a week in merely damp conditions, such as the mud of pools or damp vegetable debris. Under
such conditions the pupae changed to adults in two hours instead of the normal two or three days and practically all the larvae in the last instar (i.e. 4th) at once pupated and were ready for the final change before the pool became dry. Larvae in the earlier stages (1st and 2nd) would, however, be unable to pupate and would perish when the damp material became dry. In another test, with the larvae in mud at 62–64° F., 20 per cent, survived three days' drying; at 72° F. all died in three days.
From the point of view of control measures these observations indicate the necessity of clearing, as well as draining, pools and blocked water-courses.
Effect OF Water Impurities.
The amount of organic matter in the water naturally influences the rate of development of larvae of C. pervigilans, which were found to require 41 days to reach the adult stage in tap water, but only 18 days when some liquid manure was added.
On one occasion C. pervigilans was found breeding in a wash-tub containing suds left in to prevent cracking. The fluid contained washing soda and soap. This is only a degree less remarkable than their breeding in sal ammoniac tanks and in bark tannin solution, both of which have been observed.
The chief natural enemies of the mosquito in the Auckland district were found to be the following:—
Among the birds, the native fantail (Rhipidura flabellifera) and the native tomtit (Petroica toitoi).
Among lizards, the green gecko (Naultinus elegans).
At certain seasons frogs destroy enormous numbers of mosquitoes in the pupal stage. The stomach contents of dissected frogs showed all the stages from egg to adult, but always far more pupae. Tadpoles were not observed to eat larvae.
Among fishes, the “native trout” (Galaxias fasciatus). The repeatedly observed absence of mosquito larvae from streams inhabited by Galaxias fasciatus indicated this fish as an active natural enemy Of mosquitoes and a promising control agent. This was successfully tested both in the laboratory and field. In the laboratory the fish were observed voraciously devouring all the larvae supplied to them. In the field test, a well was used which contained about 800 larvae to the pint of water. Eight of the fish were introduced: the next day the larvae were nearly all destroyed, and none were to be found on the third day. The fish kept the well free from larvae for the following two months that it was kept under observation. On one occasion several hundred larvae were transferred to the well, but the fish devoured them all within 24 hours.
Clearly the “native trout” is a valuable controlling agent and could, with advantage, be transferred to mosquito-infected swamp drains and streams.
The carp (Cyprinus carpio) and goldfish (Carassius auratus) were found to be of special value in the ponds and fountain-basin in and about Auckland. They eat the eggs, larvae, and adult mosquitoes.
Every garden pool should be provided with carp or goldfish.
The active little native bully (Gobiomorphus gobioides) feeds eagerly on mosquito larvae, and as it is common in small creeks and ponds, no doubt helps to keep the number of mosquitoes in check. At Bethell's, on the West Coast, a lake well-stocked with G. gobioides was quite free from mosquito larvae, as were several creeks at Rawene (Hokianga) where the “bully” was abundant. At Herekino, a barrel of Water swarming with eggs, larvae and pupae was completely cleared within a day by the introduction of a few “bullies.”
The top minnow (Gambusia affinis) is a native of the United-States and inhabits shallow and sluggish waters. Its value in the-control of mosquitoes has been established in many parts of the-world.
In 1928, Dr. T. W. Hughes, Medical Officer of Health for Auckland, obtained 43 specimens from Hawaii for experimental purposes. Within 10 days they commenced to die, and in spite of changes of water and every care they were all dead in three weeks.
In the United States these fish require a good deal of attention and thrive only in suitable waters and conditions, and even if established in New Zealand, would have to compete with our native Galaxiads find bullies. The most likely places in which they might be of service are the large areas of shallow swamp waters.
The “water-bug” (Anisops assimilis) and the “water-beetle” (Rhanthus pulverulosus) which are common in ponds, troughs and tanks, are very vigorous natural enemies of mosquito larvae.
Experiments showed that Anisops assimilis takes the larvae-greedily, but will attack the pupae only when larvae are absent, and even then slowly and reluctantly. Field observations also have shown that in pools or troughs stocked with Anisops assimilis the larvae-do not even reach the pupal stage: indeed, very few reach the third instar. A field observation, frequently made, shows that although water troughs for horses and cattle usually contain “water-bugs” which keep them free from mosquito larvae, the puddles made beside them by the visiting animals' feet are not permanent enough to maintain this control. Nevertheless, these pools last long enough to permit a mosquito brood to come to maturity, and we here get the significant occurrence of larvae in a temporary puddle and their absence from a permanent water-container, the latter, however, containing an energetic mosquito enemy. These conditions apply chiefly to troughs in country towns, those in public thoroughfares in larger-towns being usually without predatory insects and therefore requiring to be emptied once in 10 to 14 days.
The aquatic larva of the beetle Rhanthus pulverulosus, which inhabits a variety of ponds, pools and artificial containers, also attacks the mosquito larvae by sucking out the body contents, audit was observed that four R. pulverulosus larvae could, between them, devour 100 mosquito larvae within two days.
The “water-boatman” (Arctocorisa arguta) also preys on mosquito larvae, but not so actively as Anisops or Rhanthus.
Dragon flies take mosquitoes of both sexes in the North of Auckland, where T. iracundus is common: while in the Aupouri Peninsula, where vast swarms of T. iracundus are on the wing by day and night, dragon flies catch enormous numbers. The remains (genitalia and hypopygia) of as many as 20 mosquitoes were found in the stomach of one small dragon fly, and a specimen of the larger Aeschna brevistyla contained 27. They did not, however, appear to be as active controlling agents as Rhanthus and Anisops.
Two species of spiders and a slim, long water-spider have been observed catching and devouring adult mosquitoes, and one of the Hydrachnia, a minute red mite, has been seen attaching itself to the thorax of the larva, the cephalothorax of the pupa and the abdominal segments of the adult.
A pool in the Hokianga district was found to contain C. pervigilans larvae, which were covered, especially on the thorax and eighth abdominal segment with large numbers of a protozoon, apparently a species of Porodon. All the larvae were thin and wasted and there were no pupae found.
Mosquitoes In Relation To Domestic Animals.
The results of investigations verified the frequent statements of farmers that mosquitoes attack their dairy herds, that the annoyance to the cows is so great that milking must be done before dark, and that the fattening cattle and dairy cows stampede into the manuka scrub to brush the pests away. The parts of the animals attacked were the udder, and about the tail, the ears and the eyes.
Poultry, pigs and sheep were also found to be attacked.
From Auckland to the far North, undeniable evidence was collected showing that mosquitoes not only attack live stock, but do so in preference to human beings. At milking time on the farms it was the cows, not the milkers, that suffered. If mosquitoes were numerous and the livestock had access to and wandered about the immediate vicinity of the residence, the inmates were little troubled: in the absence of livestock in the neighbourhood of the house, the inmates were plagued by the mosquitoes.
City And Suburban Areas.
The mosquitoes concerned are Culex pervigilans, C. fatigans and Aedes notoscriptus.
C. pervigilans may be described as the house and garden mosquito, and can be found breeding in every conceivable type of pond, drain, puddle or receptacle containing clean or polluted water.
C. fatigans is the street and gutter mosquito, breeding chiefly in barrels or pits containing liquid manure, in pools filled with seepage from manure heaps or decomposing refuse and in streams such as Motion's, Cox's and the Newmarket-Parnell creeks, which sometimes carry sewerage overflow.
Aedes notoscriptus, the mosquito of gardens and. gullies, is more selective in its choice of breeding place. It never lays its eggs where direct sunlight strikes, but makes use of a great variety of water containers and occasionally of street gully-traps, provided they are screened by grass, scrub or trees, and of drains on the sunless side of buildings.
This generalization is by no means exact: there is overlapping of breeding places, and all three mosquitoes might be found together in such a suitable spot as in foul water under the shade of trees. (Pl. 19, fig. 1.)
A very considerable, if not the greater proportion of mosquitoes which disturb residents, is bred in their immediate neighbourhood, in fact, on their own premises. It was a daily experience, while studying the city conditions, to demonstrate this to surprised people in every part of the city and suburbs.
The remedy is in their own hands. Permanent garden ponds should be stocked with goldfish or Gambusia: water tanks or barrels should be covered, guttering or spouting should be kept clean and in repair, wash tubs and similar containers should be emptied every week or ten days and gully-traps should be treated with an ounce of powdered bluestone (copper sulphate) or with kerosene, waste oil or disinfectant. Liquid manure should be screened or made up in small quantities for immediate use.
A few drops of oil should be placed in the bases of banana palms and, most important of all, long grass or weeds should be scythed or rooted out and the tins and rubbish which will almost invariably be revealed, cleared up.
Business Premises And Industrial Areas.
Many of the commercial houses in Auckland have drains round the sides and backs of buildings to carry rain water to the gully-traps. Frequently these were found to be blocked by a small quantity of earth or debris and enormous numbers of mosquitoes were breeding in the small pool thus formed. One drain, 9 inches across, 3 inches deep, and 50 feet long was found to contain 200,000 mosquito larvae and pupae; a couple of broom-sweeps would have removed the small obstruction and swept away the developing mosquitoes.
All too frequently, tins and other containers, old tyres and similar rubbish are thrown out into the warehouse yard and left “until there is enough for a load.” Meanwhile thousands of mosquitoes are bred out.
In industrial yards, private, municipal and government, there are usually lumbers of casks, barrels, oil drums and bitumen tins which hold rain water and form ideal breeding places for C pervigilans. (Pl. 19, fig. 2.)
Garages, construction shops and railway yards all have a litter of old cars or their parts, engine cabs and trucks (pl. 19, fig. 3); boat-building yards have oil and paint tins lying about and old boats and launches. All these can hold enough water for breeding innumerable mosquitoes.
Sweeping gutters and drains weekly and the frequent removal of rubbish would clear the city business premises; while in industrial and other yards barrels should be upturned or screened, and such spare parts as cannot be punctured or upturned should be sprayed with oil or copper sulphate—particularly the latter, as it would remain on the receptacle for some time.
Fire buckets almost invariably contain mosquito larvae, particularly on suburban railway stations. A copper sulphate or other insecticide should be regularly used therein.
The street gully-traps frequently are most prolific breeding-places of mosquitoes. Again and again enormous numbers have been found breeding in them. Repeated observations have shown that though the frequent flushings from heavy rains certainly reduce the number of larvae and pupae, sufficient are always left to provide for a constant emergence of adult mosquitoes through the summer and autumn. The remedy is the frequent clearing of leaves and other rubbish, to be followed by treatment with a larvicide such as copper sulphate. Oil may be ineffective through not being sufficiently evenly sprayed to form a complete film, and even if a film be formed, it will easily be broken by rain or by litter falling into the gully-trap. A female mosquito will not lay her eggs on an oiled surface: she will find some other place. She will, however, deposit her eggs in water treated with copper sulphate and the larvae that emerge will die.
Horse troughs sometimes contain enough predatory insects to control the mosquito, but this should not be relied on and they should be emptied and cleaned fortnightly.
As in private gardens, goldfish or carp should be introduced into-fountains, ponds and streams; garden water-containers should be cleared away, and holes should be made in the corners of the water-holding recesses of guns and ammunition wagons displayed as war trophies. In the cemeteries, the flower vases and containers should be emptied periodically.
Dumps Vacant Sections Creeks And Water-Courses.
The several gullies or depressions, to fill which permission is given for the dumping of rubbish of all kinds, are under present conditions a continual source of mosquito infestation. In such places every conceivable type of water-holding receptacle was found. (Pl. 20, figs. 1 and 2.) The breeding of mosquitoes in a dump can be so easily prevented by the simple expedient of ensuring that all tins thrown into it shall be rolled or beaten flat, that this should be made a strict condition of the use of a municipal dump or of the establishment of a private one. Regulations should be framed, or when they are in existence, enforced, to prevent rubbish being dumped in an unauthorised place. Generally such litter in itself bears evidence of its origin, as the labels withstand obliteration for a few weeks at least and so would give a vigilant inspector time to discover and investigate the offence.
As for vacant sections, the residents have the matter very largely in their own hands. Lack of ordinary community considerations may perhaps not deter them from littering a neighbour's vacant section with rubbish, but for their own comfort they should appreciate that from every tin they throw over a neighbour's fence a swarm of mosquitoes may return to pester them. Business firms are not without blame in this matter, for several sections were found to contain garage litter, large numbers of tobacco tins, and tins of other “packed” commodities. Carriers, too, who have been commissioned to take a lead from a commercial house to a Council dump, sometimes deposit the rubbish in a more convenient gully or section. Grass and weeds soon grow over this litter, the tins fill with water and a severe mosquito infestation results. Inspectors could help to disclose the all-too-common vacant section nuisance by ordering the scything and burning of the rank growth of weeds thereon.
The slow-moving marshy creeks running into the small lakes around Auckland and the larger creeks which become sluggish in autumn breed large numbers of mosquitoes. The remedy is to trim the sides of the creeks and remove the weeds in order to maintain a continuous flow of water. In cases in which this is ineffective, it will be necessary to treat them with a strong solution of copper sulphate at various places from the source to the mouth. Artificial means have to be used when the presence of much sewage or organic matter inhibit the life of natural enemies such as fish and insects.
In country towns the mosquitoes concerned are Culex pervigilans and Taeniorhynchus iracundus; in the country proper C. pervigilans, T. iracundus and Rachionotomyia argyropus.
On the whole, country towns suffer from the mosquito pest through conditions similar to those that prevail in the cities. The smaller towns which have no street gully-traps have a considerable growth of weeds and grass in their streets and in their semi-rural outskirts. One large northern town was in a particularly bad state: almost every vacant section, backyard, embankment and rubbish tip was involved; dumps of 100 or more tins were found at the back or sides of commercial houses, bakehouses, etc., and the local body's rubbish dump was a vast breeding ground for mosquitoes. Vigorous action by the local authority has since rectified this state of affairs, greatly to the benefit of the inhabitants.
At Kawa Kawa C. pervigilans was breeding in large numbers in pools of water almost in the town, and adults were hatching out continuously from drains, tins, hoof-holes, etc. The residents were not much troubled, however, for cows graze in several of the streets and the mosquitoes apparently confine their attention to them. Imperfect and open drains, seepage pools, rain-water tanks or small reservoirs near the town, all provide further conditions for mosquito breeding. Russell, for instance, was found to be infested with mosquitoes all the year round; the residents depending on uncovered rain-water tanks for their mater supply.
Country hotels often unwittingly provide means for breeding mosquitoes that annoy the guests and staff. Some, which lack a proper water supply, have in the yard barrels of water for washing and scrubbing. They are invariably uncovered and breed swarms of mosquitoes. In one hotel whose guests were loud in their complaints of mosquito pestering, the source of annoyance was traced to a 10-gallon drum of water in the privy. This drum was estimated to be breeding 20,000 mosquitoes a month. The addition of lysol, a teaspoonful to the gallon, put a stop to the nuisance immediately. Other causes of trouble were horse-troughs, scalding-troughs, blocked roof guttering or spouting, and bedroom water-jugs and flower vases.
Every group of farm buildings offers almost as great a variety of breeding places as exists in towns, but farm residents are rarely troubled by the mosquitoes, which devote practically all their attention to the dairy stock and poultry.
Country roads are often flanked by blocked or partly-blocked drains, by neglected water-tables, or by borrow-pits which become prolific breeding places.
The holes left by kauri-gum diggers positively teem with mosquitoes, particularly when scrub has been allowed to grow round them and provide shade.
The borders of lakes and lagoons provide breeding grounds round their edges. The most extensive mosquito breeding conditions, however, are usually those provided by interference with, or alteration of, the natural conditions through road-making and other constructional work.
The conversion of swamps and “gum-land” into agricultural land by drainage schemes is contributing enormously to the elimination of the mosquito problem in many country districts. This is well illustrated in the neighbourhood of Kaitaia and Te Kao.
In country towns and around country houses much the same control measures are required as in the towns.
There may be blocked drains and channels, swamp areas, blocked water-tables and borrow-pits that need clearing or draining and open water reservoirs that should be stocked with native trout. Probably nothing but draining and cultivation will stop the nuisance in dug-over “gum” country.
The Introduction Of Mosquitoes From Overseas.
Two mosquitoes, Culex fatigans and Aedes notoscriptus have been found in New Zealand only in vicinity of the oversea ports of Auckland, Whangarei and Nelson, from which it may be fairly inferred that they have been introduced since European occupation.
In the case of A. notoscriptus there is evidence that the conditions exist for its repeated introduction into Auckland from Sydney, and that it is still being introduced. As it is already well established here, the introduction of a few more from time to time may not be of great importance. The danger lies, of course, in the possible introduction of a disease-bearing species from overseas, a possibility rendered more likely in view of the recently-established malaria-carrying propensity of a Sydney species.
The duration of the voyage from Sydney to Auckland is entirely in favour of imported mosquitoes breeding here, for the usual, though not invariable, procedure of a female after emergence is for it to be fertilized, then to seek blood for the development of the eggs, and within one or two days to settle down and remain quiescent for three or four days before seeking water in which to lay the now mature eggs.
The four or five days' trans-Tasman journey is just sufficient for this normal procedure, and female mosquitoes on arrival in Auckland would be ready to fly ashore seeking water in which to breed.
Between May and November, 1929, an examination was made of a number of vessels arriving at Auckland from New York, Cuba, Singapore, Sydney, Suva, Niue, and Rarotonga. Officers and seamen on several of these vessels stated that they had been pestered by mosquitoes for several days after leaving tropical ports. Officers of the s.s. Lambeth, from Cuba, stated that whenever they have called there during the wet season, when mosquitoes are particularly numerous, they have been troubled with them for at least ten days after sailing. Firemen on the s.s. Waipahi, from Rarotonga, said they were pestered during the whole ten days' voyage to Auckland. Numbers of the crews of other ships made similar statements, some adding that after a few days out the mosquitoes did not bite, but remained settled on the walls, ceilings or curtains.
On the 24th May, 1929, the s.s. Maunganui was inspected immediately on its arrival at Auckland from Sydney and three live Aedes notoscriptus were secured, one in the vegetable house on the upper deck, and two between decks where horses had been accommodated on the voyage.
On the 10th June, 1929, on the s.s. Ulimaroa, from Sydney, two live female A. notoscriptus were caught in No. 2 hold. On the same day on the s.s. Tofua, from Fiji, a half-barrel with over an inch of water at the bottom was found in between decks of the No. 2 hold, in which there were several thousand larvae and pupae of Culex annulirostris, and from which adult mosquitoes were continually emerging.
C. annulirostris is a common Fijian and New Hebridean species which, fortunately, is not a disease carrier. It is, however, a persistent biter that breeds in a variety of situations, including water of considerable salinity. Two months later a barrel containing water in which a considerable number of larvae of C. annulirostris were actively swimming was discovered on the waterfront, about 300 yards west of the berthing place of the s.s. Tofua. (Pl. 20, fig. 3.) The larvae were all secured and preserved, and a thorough though fruitless search was made in other receptacles along the waterfront in which they might be breeding.
This case illustrates the danger of water-containers on the water-front as giving opportunity for live mosquitoes brought by ships to commence breeding here, and also shows that even our two coldest months, July and August, are not too severe for the larvae and adults of tropical species to withstand.
The importance of this will be realised in connection with the following two cases:—
On May 27, 1929, a live female Anopheles maculipennis, a transmitter of malaria, was secured in between decks on the s.s. Sussex, from Singapore. It was in a quiescent state and there was no blood in its stomach. A fire had occurred on the voyage and no doubt smoke had penetrated the holds, so possibly other individuals of A. maculipennis had either been driven away or killed.
On September 4 of the same year, a live female A. maculipennis was caught on the s.s. Narbada, from Samarang. Another was seen but not secured. These were found in the insulated holds, which, when loaded with rice and sago at the eastern ports, are closed down for the voyage. The holds are not refrigerated and maintain temperatures between 71° and 81° F., thus providing ideal conditions for the survival of tropical mosquitoes during the long voyage.
We do not know if these disease-bearing mosquitoes would be ripe for breeding after a long voyage, but if both sexes should arrive together the conditions for their establishment certainly exist, at present, on the Auckland waterfront.
In view of these ascertained facts—that mosquitoes certainly do arrive at Auckland from overseas, that introduced mosquitoes have been breeding on the waterfront, and that conditions in North Auckland are suitable for their establishment—it is urged that active measures be taken by the authorities to prevent their introduction and to ensure that the waterfront be kept clear of all receptacles which could contain water in which they could breed.
Key TO The Species Studied
Five genera and ten species were recorded during the investigation; they may be distinguished as follows:—
|Legs brown with pale buff spots at apex of femora and tibiae||Genus Culex|
|A row of dark spots underneath the abdomen||1. C. pervigilans Bergroth|
|No dark spots underneath the abdomen; proboscis wholly black.||2. C. fatigans Wild|
|Proboscis with a white band centrally situated.||3. C. annuliroatris Skuse|
|All three femora pale buff, other joints dark brown.||Genus Taeniorhynchus|
|Thorax with one long median and two shorter submedian straight lines.||4. T. iracundus Walker|
|Thorax with two straight submedian and two curved lateral lines.||5. T. tenuipalpis Edwards|
|Most leg-joints with white bands at apex, giving the legs a white spotted appearance.||Genus Aedes|
|Thorax with several curved longitudinal lines.||6. A. notoscriptus Skuse|
|Thorax with several straight longitudinal lines.||7. A. antipodeus Edwards|
|Thorax entirely black.||8. A. vexans Meigen|
|Joints of the tarsi white-banded, giving the mosquito the general appearance of being white-footed.||Genus Rachionotomyia|
|9. R. argyropus Walker|
|Legs and body entirely black.||Genus Opifox|
|10. O. fuscus Hutton|
Mr. Graham's investigation has disclosed the following interesting points.
Aedes antipodeus lays its eggs in mud, in which they survive even when it dries, until rain falls and development is enabled to proceed.
The effect of salinity of the water is to hasten the maturity of the pupae of Culex pervigilans. When two parts of sea-water were added to one part of fresh water containing 50 pupae, all the pupae changed to adults within 24 hours.
The endemic forest species, Rachionotomyia argyropus, was found breeding only in water tanks in the Waitakere Hills. The larvae possess anal gills as well as a siphon, so are able to remain below the surface of the water. Apparently its undiscovered breeding places are deep pools and streams.
Culex pervigilans, which may be termed Auckland's mosquito enemy No 1, is characterized by its wide variety of breeding places and the length of its breeding season.
Several species of New Zealand mosquitoes inflict bites that are irritating to most people and cause loss of sleep, and two of them, Culex fatigans and Aedes notoscriptus, cause very painful bites which may result in severe inflammation and occasionally in serious illness.
The two mosquitoes which are intolerable nuisances in Auckland city and suburbs are the native Culex pervigilans, the night-biter, and the introduced Aedes notoscriptus, the dayime biter.
One disease-bearing species, Culex fatigans, was found only in and about Auckland and Whangarei, but has also been reported from Nelson. II was probably introduced from overseas and is now established here. This mosquito can transmit filariasis (common in Fiji and Samoa), but not malaria or yellow fever.
With the exception of Culex fatigans and of a few Anopheles maculipennis (a vector of malaria) found in the holds of two ships from Singapore and Samarang respectively, no evidence was found of any mosquito capable of transmitting disease.
Graham, D. H., 1930. Mosquitoes of Auckland District, Trans. N.Z. Inst., vol. 60, pp. 205–244.
Kirk, H. B. 1923. Notes on the Mating-habits, etc., of Opifex fuscus, Trans. N.Z Inst., vol. 54, pp. 400–406.
Miller, D., 1920. Report on Mosquito Investigation in North Auckland, N.Z. Dept. Health, Bull. 3.
—– 1922-3. A Remarkable Mosquito, Bull. Ent. Res., vol. 13, pp. 115–126.