Mosquitoes are vectors of numerous diseases such as malaria, yellow fever, filariasis, dengue and chikungunya. Most female mosquitoes require a blood meal before they can produce a batch of eggs. An object capable of retaining water for five or more days is a potential breeding area for some species of mosquitoes.
The different water bodies where mosquitoes can breed are flowing streams (including drainage ditches), ponds, lake edges, swamps, natural containers (leaves of the certain plant, tree holes), artificial containers (flower pots, construction depressions, thrown plastic cups, rubber tyres), natural subterranean waters (holes dug by crabs, hoof prints) and artificial subterranean waters (septic tanks, storm and sewage drains).
Vectors
Anopheles, Culex and Aedes are the most common species of mosquitoes that spread diseases. The breeding source of these mosquitoes could be potable water, non-potable/polluted water and artificial water sources depending on the species.
These vectors develop through four states: egg, larvae, pupa and adult. Complete development from egg to adult usually takes 10 to 14 days but varies according to the species and the temperature.
Water is an important requirement for their complete development – at the egg stage to hatch and at the larval and pupal stages to grow.
Control / Management
Mosquito control can be best handled by the community and public health agencies rather than by the individual because the breeding places of mosquitoes are often situated at considerable distance from the place of annoyance. However, there are some methods that the experienced pest control operator may utilise to reduce mosquito pest problem.
Prevention
The best control mechanism is prevention. The age-old technique of closing the windows and doors during dawn and dusk is an excellent practice to prevent the entry of mosquitoes. In addition, screen like mesh wires obstruct their entry.
However, commercial buildings of today with centralised air conditioners have little openings or entry points. Yet, there are areas like the main entrance with the automatic open doors, the corridors (back stairs areas) where the windows are opened for some fresh air or as an exhaust, the openings made for renovation or the exhaust openings in the kitchen / pantry areas, can let mosquitoes inside the premises.
Control of larvae
Larvae breed wherever suitable water is available. To control larvae, either the water has to be removed or insecticides used. The appropriate larvicide to be used in the water source depends on the nature of the water body. The labels/literatures of these products specify uses and dose rates, which vary according to specific environmental situation and water source. Oils are also used to kill larvae. There are chemical larvicide, biological larvicide and new generation insect growth regulators. But, whatever is used, the efficacy, environmental damage, aquatic organism’s life and human safety need to be kept in mind before deciding on any particular product.
However, the larvicide measures done in the water source take care of only the mosquito larvae and not the eggs and the pupae already present in the water body. The advanced versions of the larvicide control are slowly moving from chemical to biological solutions and insect growth regulators, as long term effectiveness and environmental friendly measures.
Control of adult mosquitoes
Thermal fogging
Insecticides are mixed with fuel oil and burnt to create a fog with the help of the thermal fogging machines. The fog is produced by heating fuel oil in which the insecticide is diluted. The disadvantages of thermal fogging are reduced visibility restricting people’s movement, cost of using fuel oil as a carrier and the pollution caused thereof. The insecticide used may not be the major factor as perceived by the people. This method is now being replaced by ultra-low volume (ULV) application in the other parts of the world as a better and safer alternative.
ULV
Special machines are used with nozzles which break up an undiluted insecticide into microscopic droplets. With ULV application, very small amounts of chemical are used and thus, fuel oil is not burned. ULV treatment remains longer than the thermal fogging, as the tiny droplets hover around in the atmosphere for more time before getting dispersed. Both, thermal fogging and ULV application are temporary solutions. They kill only those adults which pass through the fog which disperses fast.
Mist blower and spraying
This method places the insecticides on the foliage of tree shrubs, tall grass, tree trunks and the sides of structures where resting mosquitoes may contact it. Diluted amounts of pesticides are used which will not harm plants and trees but will give better results on mosquitoes which use the green cover for shelter and harborage.
IRS Spraying
The other common method used is indoor residual spraying (IRS), wherein odourless, safe, non-fumigant, non-staining and environment friendly formulations mixed in water are sprayed or through ULV application in the indoor areas. This sort of spraying is done on all the possible resting and hiding areas like walls, false ceilings, venetian blinds, underneath tables & chairs, and dark corners. The insecticide forms a filmy coat on the sprayed surfaces once the solution dries. Mosquitoes coming in contact with this surface get killed. However, this spraying will not stop mosquitoes entering the premises but only help eliminate mosquitoes after coming inside and before causing any harm to the inmates or passing the disease as a vector.
The understanding between the companies present in the commercial buildings and the treatment measures done by the pest control companies need to be clear and perfect as to what are the efforts done and what is expected out of the same. More often than not, the mosquito control measures are done for only a particular floor of the commercial building omitting the other areas. Such measures will only give partial results, as only the part process of the mosquito management systems is followed. Mosquito control measures always give better results in an integrated approach of prevention, control and source elimination. Any one of this in isolation provides only partial results.
Ravi Chandra Application Specialist, JohnsonDiversey India