E. Technical briefs

Classification of insecticides
Chemical methods for insect control
Formulations
Propoxur
Permethrin
Deltamethrin
Malathion
Pyrimiphos-methyl
Temephos
Repellents
Impregnation of mosquito nets

Classification of insecticides

A classification enables the grouping of chemically related compounds, to deduce their toxicity and precautions for use.

MINERAL COMPOUNDS

- Mineral oils: spreading on the water surface asphyxiates and poisons larvae which are there. (mosquitoes, etc.).

ORGANOCHLORINE COMPOUNDS (NEUROTROPIC POISON)

- DDT (Dichloro-diphenyl-trichloroethane): a compound of low toxicity to vertebrates. Effective against mosquitoes, ectoparasites (lice, fleas, etc.).

Contact insecticide. Large problems of resistance and big-accumulation, not very biodegradable.

- Methoxychlorine: same as for DDT. Partially biodegradable.
- HCH (Hexachloroocyclohexane) ("Lindane", "Gamurexane"): more toxic, less persistent than DDT, but less resistance and more biodegradable.
- Chlordane: used only for controlling cockroaches and grasshoppers.
- Dieldrin: very toxic, problems of resistance. To be avoided.

ORGANOPHOSPHOROUS COMPOUNDS (ACETYLCHOLINESTERASE INHIBITOR)

- Malathion: low toxicity, used against ectoparasites and mosquitoes.
- Fenitrothion: low toxicity, used against mosquitoes (eggs and larvae).
- Fenthion: used against mosquito larvae in urban areas and in stock raising areas.
- Temephos: almost no toxicity, used against larvae in drinking water. Problems of resistance.
- Chlopyripos: urban larvicide.
- Dichlorvos: against domestic arthropods (high toxicity and vapour pressure).
- Chlophoxim: mosquito larvicide.
- Pyrimiphos-methyl: skin contact dangerous, used by spraying (aqueous dilution), widely used in public health work

CARBAMATES (ANTICHOLINESTERASICS)

- Propoxur: domestic insecticide, low toxicity.
- Carbaryl: problems of resistance.

PYRETHRIN-PYRETHRINOIDS

- Decamethrin (Deltamethrin) ("K-Othrine"): low toxicity, irritant to mucosa.
Effective alduticide, almost universally used but expensive.
- Permethrin: ditto.

Figure

Formulations

- Technical product

Active ingredient in its purest commercial form. Used almost exclusively for ultra low volume (ULV) application.

- Powder and granules

Active ingredient (0.5 to 10%) with inert carrier (talc, gypsum, etc.). Powder is used for the control of lice and fleas. Granules allow better penetration of dense vegetation.

- Wettable powder

Active ingredient (20 to 80%) + wetting agent + inert carrier. Used for preparation of aqueous solutions.

- Concentrated suspension

Active ingredient in a fine powder (10 to 50%) + wetting agent + water. Used for preparing aqueous suspensions.

- Solution

Active ingredient dissolved in a solvent. As most insecticides are insoluble in water, the solvent is most commonly gas oil, kerosene or even acetone or xylene.

- Emulsifiable concentrate

Active ingredient (25% or more) + solvent + emulsifying agent (oil). This formulation allows dilution in water later.

- Emulsion

Emulsifiable concentrate + water.

- Slow-release formulations

Slow-dissolving capsules, granules, briquettes, etc., which allow continuous release of larvicide in water.

The concentration may be expressed as weight per volume (for liquid formulations) as weight per weight (dry formulations).

INTERNATIONAL CODE OF DIFFERENT FORMULATIONS (EXTRACT)

AB: bait as a grain
AE: aerosol generator
AL: other liquids to be used without dilution
BB: bait as a block
BR: briquette
CB: concentrate for preparation of bait
CG: granulated in capsules
CS: capsules suspended in a liquid, to be diluted in water before use
DP: dusting powder
EC: liquid concentrate, to be diluted in water before use
EO: emulsion with oil, ready to use
EW: emulsion with water, ready to use
FG: fine granules (0.3 to 2.5 mm)
GB: granulated bait
GG: large granules (2 to 6 mm)
GR: granules ready for use
LA: Lacquer
MG: micro-granules (0.1 to 0.6 mm)
OF: concentrated suspension to be diluted in oil
OL: liquid to be diluted in oil
PB: bait in bars
RB: bait, ready for use
SL: liquid formulation to dilute in water
SP: powder to dilute in water
SU: suspension, ready to use for ULV treatment
TC: product in its most concentrated commercial form
UL: liquid, ready to use for ULV treatment
WP: wettable powder, for dispersion in water

Propoxur (Carbamate)

Commercial names

- Baygon
- Blattanex
- Unden

Toxicity (per os for rats)

- LD50 = 95 mg/kg

Mode of action

- Contact or ingestion

Formulation

- Powder to dilute: 1%, 2%
- Wettable powder: 50 %, 70%

Method of use

- Dusting powder

Ready to use at the rate of 1 to 2g of active ingredient (100 or 200g of powder per m2)

- Wettable powder

Dilute in water for a final concentration of 0.5 to 1% of active ingredient (powder at 50% > 20 g/litre, - powder at 70% > 1kg/litre), spray at a rate of 100 ml/m2

For use against

- Body lice
- (mosquitoes, cockroaches, bugs, fleas).

Cost

- Powder: about $3 US/kg (25kg metal drum).

Quantity to allow

- For treating 1,000 people for body lice: 40kg + losses.

Precautions

- Avoid inhaling (dust masks for treatment team).

Permethrin (Pyrethrinoid)

Commercial names

- Ambush
- Coopex
- Stomoxin

Toxicity (rats)

- LD50 = 430mg/kg

Mode of action

- Contact, ingestion

Formulation

- Dusting powder: 0.5 and 1%
- Concentrated solution: 25% and 10%

Method of use

- Dusting powder

Ready to use

- Concentrated solution

Depending on vector

For use against

- Lice
- Impregnation of mosquito nets

Cost

- Powder: about $2 US/kg (25kg bag)
- Concentrated solution: about 16 US $/litre

Quantity to allow

- For treating 1,000 people for body lice: 40kg + losses.

Precautions

- Avoid contact with mucosa (dust mask, goggles).
- Possible skin allergies.
- Do not rinse with hot water.

Deltamethrin (Pyrethrinoid)

Commercial names

- K-Othrine
- Decamethrin
- NRDC 161
- Cistin
- Decis

Toxicity (rats)

- LD50 = 135 mg/kg

Mode of action

- Contact and ingestion

Formulation

- Wettable powder: 2.5%
- Concentrated liquid: 25g/litre

Method of use

- Wettable powder

One sachet of 33g/6litres of water

- Concentrated liquid

1 litre/200 litres of water

- Spray at the rate of 1 litre/10 m2

For use against

- Flies, cockroaches (bait)
- (fleas, ants, mosquitoes, etc.).

Cost

- Wettable powder: about $3 US per 33g sachet

Quantity to allow

-1 sachet per 60 m2

Precautions

- No specific precautions

Malathion (organophosphate)

Commercial name

- Malathion

Toxicity (rats)

- LD50 = 2.100 mg/kg

Mode of action

- Contact

Formulation

- Concentrated liquid; concentration varies with manufacturer.

Method of use

- Prepare a 1% Malathion shampoo with a detergent solution. Apply 15 to 20 ml per person. Do not rinse for 24 hours.

For use against

- Headlice

Cost

- About $6 US/litre

Quantity to allow

- Depends on concentration of initial solution

Precautions

- Use a deodorised product.

Pyrimiphos-methyl (organophosphate)

Commercial name

- Actellic

Toxicity (rats)

- LD50 = 2.018 mg/kg

Mode of action

- Contact

Formulation

- Emulsifiable concentrate
- Wettable powder
- Dusting powder

Method of use

- Flies

· Actellic 50 EC: 1 litre in 40 litres of water
· Actellic 25 PM: 1kg in 20 litres of water
· Powder at 2%: ready for use

- Bait

1 g/m2 of powder at 2%, mixed with sugar half and half)

For use against

- Adulticide with immediate or residual effect on flies, mosquitoes, lice, fleas, etc.

Cost

- Concentrate at 50%: about $14 US/litre
- Powder, 1%: about $4 US/kg; powder, 2%: about $5 US/kg

Quantity to allow

- Depends on formulation used

Precautions

Temephos (organophosphate)

Commercial name

- Abate

Toxicity (rats)

- LD50 = 8.600mg/kg

Mode of action

- Contact

Formulation

- 2% solution
- Emulsifiable concentrate
- Granules
- Briquettes

Method of use

- Reservoir of drinking water: 56 to 112g of active ingredient/hectare for 2 to 4 weeks
- River: 1g/m3 of flowing water for 10 minutes

For use against

- Mosquito larvae in drinking water
- Simulium (blackfly) larvae

Cost

- 2 % solution: about $7 US/kg

Quantity to allow

- Depends on the formulation and the area to be treated.

Example: 2% solution: 3 ml/3 m3 of drinking water.

Precautions

- No specific precautions

Repellents

Repellents are chemical products used on cloth or on the skin for protection against insects.

Products used

- DEET or diethyltoluamide
- Dibutyl phtalate
- Dimethyl phtalate

Formulations

- Lotion

The active ingredient is dissolved in an organic solvent. This formulation may be used on the skin or on cloth. Only natural fibres or nylon have no risk of reaction with the solvent.

- Cream

The active ingredient is incorporated in a cream.

An attractive effect has sometimes been noted during the first minutes. For this reason, creams are not effective until after 30 minutes.

Dose

The normal dose is:

- 20g of active ingredient per m2 (cloth, mosquito net, etc.).
- 7g of active ingredient per person.

Effectiveness

This varies according to the species concerned. It may be assumed that 100% protection lasts not more than two hours, whatever the product, and that it is about 80% after 5 hours.

Precautions

- These products conform to the standards of the cosmetics industry and do not pose any particular risks for the skin.
- Only benzyl benzoate and dibutyl phtalate have a repellent action in a very humid atmosphere.
Other repellents should be applied on a dry surface; this application should be renewed if the surface has got wet (rain, excessive sweating, etc.).

Impregnation of mosquito nets

The use of mosquito nets impregnated with insecticide gives individual protection against nocturnal insects in houses (carriers of malaria), which is much more effective than using an untreated net.

Choice of insecticide
Deltamethrin 2.5% EC or WP
Or, if not, permethrin, 20 or 10% EC

Dose

-Deltamethrin: 25 mg of active ingredient per m2 of cloth (minimum 15 mg/m2)
- Permethrin: 200 to 500 mg/m2

Impregnation method

1. Determine the total area of the cloth

2. Determine the volume of water absorbable by the cloth: dip several identical mosquito nets in a known volume of water, then wring lightly; measure the reduction in the volume of water and divide this volume by the number of mosquito nets (the average is about 15 ml per m2).

3. Dilution

Determine the quantity of active ingredient per mosquito net: multiply the dosage of active ingredient per m2 by the area of the net; then determine the corresponding volume of concentrated solution and thus the factor of dilution (volume of water + volume of concentrated solution).

Example:

- area: 18.7 m2
- dose of active ingredient: 25 mg/m2
- product: deltamethrin 2.5 mg/m2
- volume of concentrated solution: 467.5 x 100 / 2500 = 18.7 ml
- volume for impregnation of mosquito net: 280 ml
- dilution = 280. 18.7, or 1/15

4. Impregnation

- One net:

Put the mosquito net in a water-tight plastic bag. Add the predetermined volumes of water and insecticide for that mosquito net.

Close the bag and knead well to ensure good impregnation, then take out the mosquito net and leave it to dry, preferably flat, to avoid dripping and the movement of the insecticide to the bottom of the cloth.

Replace the mosquito net in the bag for storage and distribution.

- Several nets:

After having determined the dilution factor, prepare a volume of insecticide solution sufficient for the number of mosquito nets to be treated. Dip the nets, then wring lightly and proceed as above.

These operations should be performed by staff trained in the use of insecticides.

Take care when disposing of excess solution to avoid damaging aquatic life and affecting water quality.

Choose a coloured cloth which dirties less easily and which is therefore washed less often.

Persistence depends on the product and the climate but mostly on washing; a persistence of six months is realistic in most cases if the net is not washed.