Mosquitoes and Mosquito Control by Micropest Pest Control Sydney
Mosquitoes (Culicidae) These blood-sucking insects, commonly about 3-6 mm in length, can be recognised on sight by most people; nevertheless many insects submitted for identihcation as mosquitoes are actually smaller or larger non-biting flies (usually midges or crane- flies). Mosquitoes are found in virtually all situations where water is available for breeding. They can be loosely classified into domestic, brackish marsh, sylvan (including tree-hole and rock-pool breeders), riverine and floodwater species.
Species of the genus Anopheles, some of which occur in New South Wales, are vectors of malaria but this disease is not, and has not been endemic in this State even though occasional cases probably transmitted by Anopheles annulipes have occurred. Filariasis occurred in the coastal northern rivers region of NSW in the early part of this century, and was almost certainly transmitted by the domestic species Culex quinquefcscidtus (previously known as Culex fatigans) but it is unlikely that this disease will be reintroduced. The species Aedes oegypti has occurred in NSW and been responsible for transmission of dengue fever in this State. However, the species has not been recorded in NSW since l948, and recent surveys have indicated that it is no longer present. Aedes ciegypti still exists in Queensland where it has been responsible for dengue transmission in recent years, so reintroduction of the mosquito to NSW should be guarded against. Outbreaks of Australian Encephalitis (Murray Valley Encephalitis virus infection) have occurred, unpredictably, in the past (the most recent in 1974) and may well occur in a similar way from time to time, especially when floodwaters cover wide areas of the State west of the Dividing Range, particularly in the Murray- Darling River basins. The principal vector is thought to be Culex cinnulirostds but other species may be involved. Another virus spread by mosquitoes, Ross River virus, causes the disease known as epidemic polyarthritis which infects humans in both inland riverine and coastal areas of NSW on a regular, possibly annual basis. Little is known of the natural history of this virus, but a number of mosquito species may be involved in transmission to humans depending on the circumstances - probably principally Culex annulirostris in inland regions and Aedes vigilox in coastal areas. Finally, also of some relevance in the context of this manual is the transmission of dog heartworm (a filarial parasite) by mosquitoes in both urban and rural centres of NSW. Although little is known of the range of mosquitoes involved in infecting dogs with this parasite, there is evidence that the peri- domestic Aedes notoscriptus is a vector in urban areas, Culex dnnulirostris is a vector and likely to be important in inland riverine regions, and Aedes vigilax may be important in some coastal areas.
Life cycle The female mosquito lays her eggs on the surface of water, on surfaces adjacent to water like the damp area above the actual water line of a rock pool, or on drying-out muddy areas which may not be covered again by water for weeks or months. Those laid on the water surface will usually hatch within three days; those laid elsewhere are resistant to drying and will not hatch until actually immersed by a rising water level or inundation. A phenomenon of delayed hatching is also involved so that not all eggs hatch at the first immersion. Eggs hatch to larvae which are fully dependent on water. The entire larval life and the later pupal stage take place in water. Should the water evaporate before the larval stages are complete death ensues before the adult stage is reached. From the pupa emerges, at the surface of the water, the adult which then embarks on a terrestrial existence. The minimum time required for completion of the life cycle from hatching of the egg to emergence of the adult is four days but this rapid breeding only occurs in hot weather in temporary ground pools. It could occur with floodwater or brackish marsh species but not with others. Usually the aquatic phase is at least a week to IO days but can be much longer in some, usually unimportant, species. Adults usually mate in the vicinity of breeding grounds within the first day after emergence. The males, which do not suck blood, are short-lived while the females seek a blood meal, usually necessary for the maturation of eggs. It is not easy to give an average life for a female mosquito as it will vary from species to species and within species depending on the individual ability to remain in satisfactory conditions of humidity and temperature. Nevertheless females are quite capable of several blood feeds, laying eggs after each. They may even take blood more frequently than is required for egg maturation if opportunities for feeding are readily available. The adult life span may well be several weeks, not merely a few days, since their behaviour characteristics lead them to avoid adverse environmental conditions as far as possible Certain types of water are suitable or unsuitable for the breeding of particular species depending on the specific selection of special types of water, or surfaces, by the female for egg laying.
Domestic mosquitoes attack humans with greater frequency and constancy than any others yet they are not complained about to the same extent as those which occur occasionally in high density biting out of doors. However, the domestic nuisance must be recognised and should be the first to be attacked in any mosquito abatement programme. There are two species commonly behaving as domestic mosquitoes in New South Wales, namely Culex quinquefasciotus (fG[lgCll’lS) and Aedes riotoscriptus.
Because they breed in close proximity to houses domestic mosquitoes are the primary responsibility of residents. Extra-domestic breeding may occur and become a local authority problem. This can be important 'in the case of Culex quiriquefosciatus but far less so with Aedes notoscriptijs. l- ouseholders are’assisted by certain local government regulations relevant to mosquito control and if these are adhered to the problem can be minimised. Despite the occasional, more spectacular ctivity of certain day-biting species it must be emphasised that most mosquito attacks are xperienced at or soon after dusk outdoors by Aedes riotoscriptus and indoors at night by Culex quiriquefoscicitus.
This ubiquitous species is an introduction to Australia. ii is active at night,and spends much of its time inside the house while digesting its blood meal. ln the morning engorged females will be seen on the walls and ceilings of the bedrooms; later it will seek rather darker situations in open cupboards and wardrobes, and behind doors. Since most biting takes place after people have gone to sleep it may often be unnoticed although the buzz as it flies to the attack is irritating to some.
Culex quinquefosciotus probably feeds far more on poultry, when available, than on humans, but as it is a very abundant species its importance as a pest is considerable. lt breeds in many types of domestic water but the speed of development and numbers produced are considerably increased by the degree of pollution. A very important source of large numbers of this species is an unscreened septic tank. Other polluted areas are ponded effluents from septic tanks, domestic sullage, ground pools contaminated with human or animal faecal material and liquid manure drums, but any water-holding containers may also be utilised, even flower vases inside the home. Less obvious but portant breeding sites in urban areas occur below ground level. These include gullytraps adjacent to houses and catch basins in streets. lnfestations in commercial areas of cities are usually derived from catch basin breeding and it is paradoxical that the nuisance can be greatest in dry seasons when atch basins are not flushed out but are often replenished by water-carts used for street leansin!Cu/ex quinquefcisciatus has been observed emerging from the vent stacks of septic systems. l-low important this source may be is hard to assess but there is no reason why the vent stack opening should not be screened.
Although the essentially domestic breedinghabitats have always been stressed and remainimportant there are circumstances, increasing inWéquency, wherein Culex quiriquefosciotus is an environmental problem. This has been seen in country towns in New South Wales, more recently in parts of Sydney, and is also recorded in overseas centres. The situations derived from industrial pollution are easily demonstrated but others occur where the cumulative effects of the individually inconspicuous degrees of pollution resulting from people living adjacent to easements and natural drainage lines convert creeks to Culex quinquefosciotus breeding habitats causing an unusually widespread infestation of domestic mosquitoes, This problem is also intensiied in dry periods.
Public awareness of the possible breeding places for this species is most necessary as quite a number of its habitats can be eliminated. Adherence to regulations governing the installation of septic tanks overcomes problems from this source but where screens are used it should be remembered that the reliable life may be as short as IO years without renewal. Management of gardens and backyard fowl runs should take into account the possible breeding sites associated with these activities. Below ground habitats are best treated regularly with a Elm of oil, fortnightly intervals being quite adequate.
The significance of non-domestic breeding varies in different townships. Important factors are sullage disposal practices (waste sometimes discharged into street gutters A so-called wet gutters); condition of street gutters whether curbed or formed in soil, and whether adequately or nadequately graded; the presence of water- holding pits such as disused clay pits which may also be used for rubbish dumping; stormwater channels which may be inadequately graded for dry period flow; culverts improperly constructed and hence promoting ponding; and the presence of aturalcreeks subiect to pollution in residential areas. Certain industrial wastes or even the water used for washing utensils may create pollution along surface drainage lines as from milk depots, butter factories, breweries, abattoirs and similar industries. l-lere again dry season problems may be encountered because of cessation of normal flushing of water courses.
lnside the home protection can be afforded by screening but this, for mosquitoes, must include windows and ventilators. The latter can best be screened at the time of construction of the house. Nevertheless, freedom from this pest species is often gained, even in unscreened houses, by careful attention to peri-domestic breeding places.
With regard to insecticidal control, adults in the home can be killed adequately with pyrethroid aerosols. but with the domestic mosquitoes reliance on insecticides is unsound in principle especially for larval control. To use insecticides on the larval sites of these species, the breeding places must first be found. Then it is often simpler to eliminate them or protect them by screening and so on than to treat them with insecticide. However, if insecticides are necessary, the chemical temephos ("Abate") or the biological product Bacillus thuringiensis isroelensis (Bti) are recommended for npolluted lar/al habitats, and for residual surface spraying maldison orpermethrin are recommended.
Culex quinquefasciatus control in urban areas is one of the most difncult mosquito control propositions because of the varied exposed, enclosed and subsurface breeding grounds involved. Dissemination of information to the public and assistance by inspection from local authorities together with an enlightened approach to the problem of disposal of wastes are essential atthe outset.
Aedes notoscriptus is a native species which naturally breeds in tree-hole and rock~pool habitats in forests. lt has rapidly exploited the domestic environment in most of NSW, breeding in containers outdoors close to houses. lt bites predominantly at and after dusk, but will also attack at dawn and during the day in sheltered situations. lt is predominantly an outdoor mosquito, but will enter houses to bite.
Eggs of this species are resistant to drying and can survive for months in a moist atmosphere, such as can be found in some artincial containers such as rainwater tanks. The type of water preferred for the larval habitat of Aedes notoscriptus is relatively clean, although pollution by leaf debris is cceptable. Around the home, important breeding sites are provided by any water-holding tins or plastic containers, bottles, pot plants, discarded tyres, and in particular blocked roof gutters.
For control of this species, dissemination of information as to its breeding sites is important for public co-operation in reducing the breeding population by reducing the availability of container habitats. Collection and disposal of hard waste would have a considerable deleterious effect on populations of this species in domestic environments. As with Culex quinquefasciatus, homes may be protected by screening, and insecticides (other than to kill adults within the house) are generally an inadequate approach to the problem as there are no breeding places around the home which cannot be eliminated or rendered ineffective by mechanical means.
The mosquitoes most commonly complained of along the New South Wales coastline are derived from brackish marshes or more specihcally the low- lying areas inundated from time to time by king tides. The dominant species in this habitat is Aedes vigi/dx, a small but robust species capable of distributing itself widely, readily up to IO km from its breeding areas. Actually it has been detected at distances of 50 km from the coastline but in too few numbers to be a problem. Aedes vigilax is an out-of-doors biter and quite a nuisance in gardens during the late afternoons. Near its breeding places, day-time attacks may be intolerable.
Eggs are laid on the breeding grounds and remain viable until covered with water. This is very temporary and shallow and hence warm, and development is rapid. By the time the adults have become a nuisance breeding has ceased and the pools have probably dried up and at this time nothing can be done. Mangrove swamps are a good indication of potential breeding areas but any disturbance of native mangrove grovifth, short of full reclamation, is likely to intensify the problem.
ln urban areas the inevitable processes of development and expansion gradually bring about the elimination by reclamation of low-lying waste lands at the limits of tidal iniltration. This is usually done without thought for mosquito control but as a result of the need for large areas of flat land (e.g. airports, parks and playing Relds), or for expansion of industrial areas. A realisation of the nevitability of this process, and of the pest hazards associated with tidal flats, could lead to changed iews of priorities in land development and also of usage. This could result in an acceleration of eclamation activities with multiple benetits. Reclamation for mosquito control, so important in the first three decades of this century, was interrupted by the depression and World War ll and later became unfashionable because of rising costs and the more spectacular achievements of modern insecticides. Once again we are beginning to realise that insecticides are not an adequate answer to many of these problems. Also, the need for removal of siltation in waterways together with the economic operation of sand pumps serving the dual purpose of deepening below water level and filling above, makes reclamation once again a very realistic approach to this problem. Due onsideration needs to be given, of course, to the concerns of environmental interests especially where the area is associated with fish and other aquatic organisms and bird nurseries.
If insecticides have to be used one modern approach requires knowledge in detail of the area susceptible to mosquito breeding in each particular problem area and the use of the insecticides, which must be residual ones, prior to inundation and consequent hatching of eggs - so-called prehatching treatment. Although it is theoretically sound little use is made of this method. However, since the emergence of plagues of brackish marsh mosquitoes can be predicted, insecticides can also be used to kill the adults at the time of mass emergence and prior to dispersal. Timing is fairly critical but methods of aerial application are becoming much more economic. There are very few insecticides which meet with approval for use in this way. ln Queensland aerial applications of temephos and naled have been used against Aedes vigilax but there has been no similar programme n New South Wales. Maldison is also suitable for aerial or ground application against adults, but temephos is the recommended larvicide.
The principal pest mosquito in the inland riverine and irrigation areas of New South Wales is Cu/ex cinriulirostris, which is important as a major arbovirus vector. While it is not normally considered to be a domestic species, in rural communities closely associated with natural or man-made breeding sites, this species is often the mosquito responsible for most biting around the home - usually outdoors. Typically this mosquito is associated with swamps and billabongs in its natural habitat, but it rapidly exploits irrigation water hat is inadequately disposed of, and rainwater that persists in ill-drained depressions. Because of the numerous and widespread lar/al sites, often quite large in area, larval control is expensive whether undertaken using chemical or engineering techniques. Larval control can be achieved using weekly applications of the organophosphate insecticide temephos or formulations of Bacillus thuringiensis israe/erisis, but the area of mosquito breeding often restricts effectiveness of such methods. Adult control is usually a matter of protection from biting by suitable clothing or chemical repellents, or simply avoiding exposure at the time of peak biting - which for this species is mostly within the Hrst hour or two after sunset. In arbovirus disease outbreaks, space spray or fogging applications of maldison could be undertaken by health authorities to kill possibly infected adult mosquitoes, and thus control or prevent transmission within a community.
There are, of course, other non-domestic species which are a nuisance to humans under special circumstances. These are either too intermittent in occurrence for abatement to be contemplated (floodwater species on the western plains); or problems associated with major rivers for which solutions are unlikely to be sought until the affected population is of far greater density, or problems associated with irrigation areas where daytime attack on rural workers may be a problem of some magnitude. lt is possible that mosquito densities in irrigation areas will tend to increase rather than decrease in the future especially if areas under irrigated pasture increase considerably. If this proves to be so attempts will almost certainly be made to practise mosquito abatement. Surface grading and water management will be important, in addition to proper maintenance of distributing canals and tail drains, although the latter already deserve more attention.
Cardinal points in mosquito control
(a) lt is essential that the mosquito species responsible for annoyance be identified.
(b) Suficient knowledge is available about individual species for the type of problem to be determined following identification.
(c) The actual problem must be deined (domestic, estuarine, single household, environmental, nuisance or disease potential, and so on).
(d) The level of responsibility should be established.
(e) Education at both the individual and public authority level could lead to considerable improvement, in the latter case especially in the planning of works and urban development.
(f) Successful mosquito abatement on an environmental scale is never achieved without strong support at an administrative level, adequate Hnance and trained personnel to do the job on a full-time basis.
Mosquito control price list
Micropest provides the following Mosquito pest control service with an approximate price. Please don't hesitate to ring because we do have specials from time to time and we are flexible.