Space spraying relies on the production of a large number of small insecticidal droplets intended to be distributed through a volume of air over a given period of time. These droplets deliver a lethal dose of insecticide to target insects upon impact.
The traditional methods for generating a space spray include thermal fogging (whereby a dense cloud of insecticide droplets is produced, giving the appearance of a thick fog) and Ultra Low Volume (ULV), whereby droplets are produced by a cold, mechanical, aerosol-generating machine.
Since large areas can be treated at any one time, this method is a very effective way to rapidly reduce the population of flying insects in a specific area. Since there is no residual activity from the application, it must be repeated at intervals of 5-7 days in order to be fully effective. This method can be particularly effective in epidemic situations where rapid reduction in mosquito numbers is required. As such, it is commonly used in urban dengue and Zika control campaigns.
Effective space spraying is dependent upon the following specific principles:
1. Target insects are usually flying through the spray cloud (or are sometimes impacted while resting on exposed surfaces). The efficiency of contact between the spray droplets and target insects is therefore crucial. This is achieved by ensuring that spray droplets remain airborne for the optimum period of time and that they contain the right dose of insecticide. These two issues are largely addressed through optimizing the droplet size.
2. If droplets are too big they drop to the ground too quickly and don’t penetrate vegetation or other obstacles encountered during application (limiting the effective area of application). If one of these big droplets impacts an individual insect then it is also ‘overkill’ since a high dose will be delivered per individual insect.
3. If droplets are too small then they may either not deposit on a target insect (no impact) due to aerodynamics or they can be carried upwards into the atmosphere by convection currents.
Misting is the dispersal of a liquid fog of insecticide into an outdoor area to kill adult insects. It has been regularly used in public health and pest control programs, including use as an emergency response to dengue epidemic