Ask the Expert - Mosquito Space Spraying

A brief introduction to the mysteries of Mosquito Space Spraying.

Print page

Of all the application technologies we as Professional Pest Managers employ, without doubt Space Spraying is the one that appears to have the most mystery surrounding it. Yet the technology to apply products via fogging or ULV misting is no more complex than any other we use. It is probably that for most of us, this technology is not used with the same frequency as our trusty hand tank for instance. There is no doubt the equipment used is different to anything we use. Perhaps its ability to quickly treat large areas can be daunting but the principles by which they operate are well proven and well within the capabilities of Professional Pest Managers.    

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 short period of time. When these droplets impact on a target insect, they deliver a lethal dose of insecticide. 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.

With ULV, droplets are created by mechanical shearing of the insecticide as it flows through the nozzle. An upward nozzle angle directs the droplets upward and they come down via gravity.

In contrast with Thermal Fogging, the insecticide formulation is vaporised by high temperatures, which when contacting cooler outside air condenses into droplets. The nozzle is directed towards the ground and as the hot air rises the droplets are carried upward.

Space-spraying (Fogging or ULV Misting) can be a highly effective means of killing large numbers of insects (mainly flying adults) in a short space of time. It is a method that can be employed with great effect against insects such as mosquitoes and flies and in enclosed situations is a very useful method to 'clean up' stored-product moths and cockroaches. 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. Suitable and appropriately calibrated equipment can deliver small amounts of active ingredient over a large area with excellent results. It is a technique that is used as a method of choice for rapidly bringing adult mosquito numbers down in vector-borne disease epidemics (eg. dengue).

Timing of application – insect activity: Because a space-spray is designed to target insects mainly when they are flying (or occasionally resting on open exposed surfaces) it is important that application is timed to coincide with peak activity times for the target insect in order to maximise results. This will vary with the insects in question but generally housefly flight activity peaks in the early morning or the late afternoon and for mosquitoes it is commonly late afternoon and early evening.

Timing of application – atmospheric conditions: Climatic conditions should also be considered when spraying - temperature inversions which commonly occur early mornings and evenings are conditions conducive to spray remaining at ground level and not disappearing into upper air currents where insects would not be contacted. Spraying should be avoided during the heat of the day as convection currents and winds will limit efficacy.

Product: The ideal product for use in space sprays should contain an active ingredient that is rapidly acting at low dose rates; have low mammalian toxicity (to reduce risks to the operator, the public and the environment) and be suitable for application through a range of equipment. Lack of residual life of the active ingredient is also desirable so that impact against non-target species and the environment is minimised when droplets settle on surfaces.

Whilst most products are based on hydrocarbon solvents and require mineral oils as their diluent, some new products that are water-based also have built in anti-evaporant technologies so that droplets remain viable for longer which means more time to come into contact with their target. Without this technology, water based formulations produce droplets that evaporate affecting droplet size and efficacy.

Opportunities? If you are interested in the highly effective and efficient technology that is space spraying, speak with your local equipment specialist/distributor and Bayer product representative. For those involved in commercial pest control accounts containing suitable warehouses requiring treatment, this technology is a must have in your program. For those that want to be involved in mosquito control in their business, contacting the MCAA (Mosquito Control Association of Australia) and enrolling in their mosquito control course is highly recommended. Whilst the majority of mosquito management is conducted through programs controlled by local and state government organisations, there are opportunities for us Professional Pest Control Operators to contribute in the jurisdictions in which we operate.


To view the latest issue of Bayer's Public Health Journal please visit