Spotters in "Environment and Health: Mosquito control Measures" for CFM & MPH students

The integrated approach of mosquito control:

This is an approach that avoids the excessive use of any one method (e.g insecticides) but tries to combine one or more methods with a view to obtain maximum results with minimum inputs and also to prevent environmental pollution with toxic chemicals & development of insecticide resistance. The various methods of mosquito control are as follows:

1. Anti- Larval Measures:

(a) Environmental Control:

Important Points:

Source reduction: Mainly the elimination of mosquito breeding places by minor engineering methods such as 

• Filling- of cesspools & open ditches and arrangement for adequate collection, removal, and disposal of sewage & wastewater.
• Leveling & getting rid of water-holding containers such as discarded tins, empty pots, broken bottles, coconut shells, etc.
• Drainage of breeding places, and 
• Water management (e.g intermittent irrigation) & removal of aquatic plants or destruction by herbicides.
• Rendering the water unsuitable for breeding- changing salinity of the water.

(b) Chemical control:

(i) Mineral Oils:

Important Points:

• One of the oldest methods.
• Widely used oils are diesel oil, fuel oil, kerosene, various fractions of crude oil & special oils (e.g mosquito larvicidal oil).
• Mechanism of action: Oils kill larvae & pulse within a short time by spreading over the water surface & forming a thin film that cuts off the air supply.
• It also has specific toxic action on stages of insects.
• The application rate is 40 to 90 liters per hectare once a week.
• Disadvantages: Oils render water unfit for drinking & kill fishes.

(ii) Paris green/ Copper acetoarsenite:

Important Points:

• It is an emerald green, micro-crystalline powder practically insoluble in water.
• A good sample must contain 50% arsenious oxide.
• Mechanism of action: It is a stomach poison. Kills mainly surface feeders (e.g anopheles larvae) but bottom feeders can also be killed if the special granular form is applied.
• Applied as 2% dust prepared by 2 kg of Paris green & 98 kg of diluent (e.g soapstone powder or soaked lime) in a 'rotary mixer' and the resulting mixture is of size 20-25 microns.
• Dusting is done by hand blowers or rotary blowers.
• The recommended dose is 1 kg of actual peris green per hectare of water surface.
• It does not harm fishes, humans, or domestic animals.

(iii) Synthetic insecticides:

Important Points:

• The most effective insecticides are Fenthion, Chlorpyrifos, and Abate.
• Mechanism of action: These organophosphorus compounds hydrolyze quickly in water. Abate (at a concentration of 1.0 ppm) is a very effective larvicide and the least toxic.
• Dosage: Abate 56-112 g/ ha, Malathion 224-672 g/ ha, Fenthion 22-112 g/ ha, Chloropyrifos 11-16 g/ha.
• The organochlorine compounds (e.g DDT, HCH) are not recommended due to their long residual effect, water contamination & an increased risk of developing resistance.

(c) Biological control:

Important Points:

• Gambusia affinis & Lebister reticulatus (Barbados Millions) are fishes that feed readily on mosquito larvae.
• These can be used in burrow pits, sewage oxidation ponds, ornamental ponds, cisterns, and farm ponds.

2. Anti- Adult Measures:

(a) Residual sprays:

Important Points:

• These are most effective against adult mosquitoes. DDT is the insecticide of choice but where DDT resistance is encountered, malathion, propouxur & lindane are recommended. 
• Dosage: DDT 1-2 g/ m2 for 6-12 months, Lindane 0.5 g/m2 for 3 months, Malathion 2 g/m2 for 3 months, OMS-33 2 g/m2 for 3 months.

(b) Space sprays:

Important Points:

• These formulations are sprayed into the atmosphere in the form of a mist or fog to kill insects. Common space sprays are 
• (i) Pyrethrum extract- the active principle (pyrethrin) is a nerve poison & kills insects instantly on mere contact. Dosage is 1 oz (0.1%) per 1000 C. ft. of space. No residual action.
• (ii) Residual insecticides- Extensively used insecticides used for ULV (ultra-low volume) fogging are malathion and fenitrothion.

(c) Genetic control:

Important points:

• Control of mosquitoes by genetic methods such as sterile male technique, cytoplasmic incompatibility, chromosomal translocation, sex distortion, gene replacement has been explored well.
• Advantages- These are cheaper, more efficient & no vector resistance.

3. Protection Against Mosquito Bites:

(a) Mosquito net:

Important points:

• Offers protection during sleep.
• The material should be white to detect mosquitoes.
• The best pattern is a rectangular net.
• The size of openings in the net should not exceed 0.0475 inches in any diameter.
• The number of holes in one square inch is usually 150.

(b) Screening:

Important points:

• Screening of buildings with copper & bronze gauze having 16 messes to the inch is recommended.
• The aperture should not be larger than 0.0475 inches.
• Screening of buildings is costly but gives excellent results.

(c) Repellents/ Culicifuges:

Important points:

• Used mainly for application on the skin.
• Diethyltoluamide (deet) is an outstanding, all-purpose repellent & remain active for 18-20 hours against C. fatigans.
• Other repellents are indalone, dimethyl phthalate, dimethyl garbage, ethyl hexanediol, etc.
• The chief advantage is the short duration of protection.

References:

1. Park, K. (2019). Park's textbook of preventive and social medicine. 25th. Jabalpur, India: M/S Banarsidas Bhanot.
2. Kadri AM. (2019). IAPSM's Textbook of Community Medicine. 1st. New Delhi, India: Jaypee Brothers Medical Publishers (P) Ltd.
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