Vector Control - Methods for Use by Individuals and Communities (WHO, 1997, 425 p.)
 Chapter 9 - House-spraying with residual insecticides
 Insecticides for residual spraying
 (introduction...) Characteristics of good residual insecticides Resistance Formulations Dosages and cycles Type of sprayed surface Commonly used insecticides Preparation of insecticide suspension

### Preparation of insecticide suspension

If the standard spraying procedure (see p. 376) is adopted the spray liquid will be applied at a rate of 40ml per m2 or one litre per 25m2. This amount of suspension normally stays on the surface without run-off.

Water-dispersible powder

One litre of spray suspension can be prepared using the following formula:

where:

X = weight of water-dispersible powder required (g)
Y = recommended application rate (g/m2)
C = concentration of active ingredient in formulation (%).

 Example DDT (75% water-dispersible powder) is to be sprayed at a dosage of 2g/m2. For an eight-litre tank, the amount of water-dispersible powder needed is: 8 × 66.6 = 533.3g The insecticide should be packed in small bags containing 533.3g each. In the field, put water in a mixing bucket until the eight-litre mark is reached. Mix the contents of one bag with the water, using a wooden paddle. Pour the solution into the sprayer through a funnel with a screen, close the tank and shake it.

Emulsifiable concentrate

To prepare an insecticide suspension from an emulsifiable concentrate, use the same formula as for the water-dispersible powder, with:

X = amount of emulsifiable concentrate needed (ml)
Y = recommended application rate (g/m2)
C = concentration of active ingredient in formulation (%).

To prepare one litre of suspension, add X ml of emulsifiable concentrate to (1000 - X) ml of water.

 Example DDT (25% emulsifiable concentrate) is to be sprayed at a dosage of 1g/m2. To prepare one litre of suspension, add 100ml of emulsifiable concentrate to 900ml of water. For an eight-litre tank, add 800ml of emulsifiable concentrate to 7200ml of water.