Insecticides are usually manufactured as pure substances but are processed into forms suitable for safe and effective application. Different formulations have varying characteristics important for their use. Operators must select the appropriate application method within safety constraints, requiring an understanding of different application types and available equipment.
Insecticide Formulations
Insecticides are usually made as fairly ‘pure’ chemicals, known as ‘technical material”, with purity ranging from 90-99%. This material can be in different forms like waxy solids, powders, or liquids. However, because it’s highly toxic, expensive, and hard to dilute, it’s not useable as is. So, manufacturers process it into usable forms through a process called formulation. Formulation improves its effectiveness, storage, ease of preparation, application, and safety. The final product might be ready to use or need dilution (eg with water) on-site.
The way insecticides are made into different forms can affect how well they work against pests. For instance, some forms can soak into porous surfaces like bricks, while others stay on the surface. These differences matter because they can affect how well the insecticide works. When trying to control insects, it’s crucial for the person applying the insecticide to make sure it actually touches the insects. To use insecticides effectively, efficiently, and safely, it’s important to understand the different types of insecticide forms.
Common components of formulations
Before diving into particular types of insecticide formulations, it’s important to understand the different terminologies used to describe various components:
Active constituent. The active constituent, sometimes called ‘active ingredient’, is the part of the insecticide that actually works against pests. It’s usually listed on the label by its chemical name along with how much of it is in the product.
For example, you might see: “ACTIVE CONSTITUENT: 800 g/kg propoxur” on the label.
Diluent. The diluent in a formulation is any substance added to lower the concentration of the insecticide. Common diluents include oil or water in liquid formulations and talc or clay in formulations like dusts.
Solvent. A solvent is a liquid that can dissolve a chemical. Some chemicals dissolve easily in water, while others need special solvents like aromatic hydrocarbons such as toluene or xylene. In formulations, solvents often also act as diluents. In liquid formulations, solvents typically evaporate after application, leaving behind the insecticide residue.
Attractant. A component in baits that lures the specific target pest.
Surfactant. Surfactants, also known as surface-active agents, are chemicals added to liquids to change how they spread, soak, disperse, or mix with other liquids (properties influenced by surface tension). They are like detergents. In insecticide formulas, there are two main types of surfactants to consider:
- Emulsifiers – these help mix oil-based liquids with water. Usually, oil and water don’t mix; they stay separate. But with emulsifiers, the oil and insecticide in it form tiny droplets that spread evenly in the water. This often makes the mixture look milky because of how light bends through it.
- Wetting agents – These help mix solid insecticide particles with water. Usually, a dry powder doesn’t spread evenly in water. But when a wetting agent is added, it helps the powder disperse evenly throughout the water. Wetting agents are also used to improve the wetting ability of water-based sprays. This can be helpful when spraying for pests like webbing spiders or foliage pests. It’s best to use specific wetting agents designed for this purpose.
Synergist. A synergist is like a sidekick for insecticides. Even though it does not kill insects on its own, it boosts the potency of the insecticide it’s mixed with. One of the most well-known synergists is piperonyl butoxide, often mixed with natural or synthetic pyrethrins. Synergists likely work by stopping insects from getting rid of toxins, making the insecticide more effective against them.
Types of Formulations
In urban pest control operations, there are several types of insecticide formulations used. These include liquids that can mix with water (Emulsifiable Concentrates), powders that dissolve in water (Wettable Powders), liquid mixtures with solid particles (Suspension concentrates), powders applied as dusts, attractants mixed with poison (Baits), and sprays released into the air (Aerosols/Space Sprays). Here are some basic examples of what these mixtures might contain, but remember, actual products may vary.
Oil concentrates used to be simpler and more common in the past, but they are not as popular now. These concentrates contain the insecticide dissolved in a strong solvent. Users could dilute them further with oil-based substances like kerosene or diesel, since water does not mix with them. People used to spray this mixture on surfaces, like timber to control borers, but that is less common now. Nowadays, they are mostly used for fogging equipment to spray in the air.
However, there are drawbacks to using oil concentrates:
- They are expensive because the solvent is costly.
- They are bulky and costly to transport.
- They can react with certain surfaces like lino, wallpaper, or rubber.
- They are flammable, especially in enclosed spaces.
- They may react with equipment parts like gaskets and hose lining.
- They soak into porous surfaces easily, which can make the insecticide less effective, especially for surface pests like cockroaches.
Oil-based mixtures have one advantage: they are good at getting into porous surfaces. If you need to treat something like wood for insects that bore into it, spraying with an oil-based mixture is better because it can penetrate deeper compared to water-based sprays.
Emulsifianle Concentrates (ECs)
The EC formulation is widely used in urban pest control. Most insecticides dissolve in strong oil-based solvents like toluene, but this mixture does not mix with water. To make the oil phase (insecticide + solvent) mix with water, an emulsifier is added.
So the components of an EC are: insecticide + solvent + emulsifier = EC
When mixing the product with water, it creates an ‘oil in water’ mixture where tiny drops of insecticide and solvent are spread evenly in the water. ECs are mainly used for spraying surfaces, whether it’s saturating soil for termite control of treating surfaces for cockroach control. They can also be sprayed into the air with misting equipment.
The advantages of ECs include:
- You can mix concentrate with water, which is inexpensive, usually readily available on site (no need to bring with you), and is not flammable.
- The spray is often harder to see on surfaces compared to other types of sprays.
The disadvantages of ECs include:
- Because of the all-liquid system, the insecticide mixture sprayed onto porous surfaces can be absorbed to some extent, which might not be good for controlling pests like cockroaches.
- Sometimes, certain surfaces might get stained by the water in the mixture, but this rarely happens.
- They might harm plants (phytotoxic) if sprayed on them.
While most ECs mix well with water to form stable mixtures, it is good to give them a little shake to make sure everything is mixed evenly. It is best not to leave insecticide mixtures sitting in the tank overnight, especially for insecticides like organophosphorus, as they might break down. Many of the insecticides used in urban pest control are formulated as ECs.
Wettable Powders (WPs)
These are sometimes called water-dispersible powders, WPs are insecticides that do not dissolve in water or other liquids, instead, they suspend. They have finely ground insecticide mixed with a solid substance like talc or diatomaceous earth, along with wetting agents (similar to detergents) that help the powder mix with water to make a suspension.
The constituents of a WP are: insecticide + diluent + wetting agent = WP
The diluent (or carrier) in WPs can be mixed or coated with the insecticide. The mixtures are often packaged as dry powder in measured packets and then mixed with water when used.
WPs are mainly used as surface sprays, such as for controlling cockroaches.
Their advantages include:
- They can be mixed with water, which is cheap, easy to find, and not flammable.
- They work well on porous surfaces like wood or bricks because even if the water evaporates or gets absorbed, the insecticide particles stay behind on the surface available for crawling insects to pick up.
- They are unlikely to harm plants.
One drawback is that they might leave a visible residue on surfaces, but this is usually not a big issue and can be wiped away easily.
Because WP mixtures contain solid particles suspended in liquid, they are somewhat unstable: the solid particles tend to settle at the bottom of the container over time. To guarantee an even spray mixture, frequently agitate the spray tank. Also, because of these solid particles, some spraying equipment might experience more wear and should be rinsed thoroughly with clean water after use. It’s not a good idea to store WP mixture in the spray tank because it can lose effectiveness after a day of being mixed with water. Many insecticides, including some organophosphorus and carbamate types, are formulated as wettable powders.
Suspension Concentrates(SCs)
The constituents of a suspension concentrate are: insecticide + diluent + wetting agent = SC
This formulation seems similar to wettable powders (WPs), but there’s a difference: while WPs are dry, SCs come as liquid concentrates. SCs usually have a finer carrier (a substance that holds the active ingredient), contain deionized water, and might have a bactericide and antifreeze added to prevent mixing issues.
Since SCs have solid particles suspended in water, it is crucial to shake the liquid concentrate well before using it and to keep agitating the spray mixture during use to prevent the material from settling out.
Micro-encapsulated concentrare (MEs)
These products are sometimes called ‘slow-release formulations’ because they contain insecticide enclosed in tiny capsules that look like small spheres. The insecticide is released slowly from these capsules over a long period.
Advantages of MEs include:
- Long-lasting effectiveness
- Easily picked up by insects and can be ingested during grooming
- Typically odourless
- Usually safe for plants
Disadvantages of MEs include:
- Need for frequent stirring during application
- Can be more costly
- Some types may leave a visible residue on certain surfaces
Dusts
Dusts are frequently used in city pest control methods. Some insecticidal dusts are made up solely of finely powdered insecticides, like certain boric acid products and other inorganic insecticides. More commonly, insecticidal dust contains a small percentage (usually between 0.5% to % 5.0%) They are a dry mixture of finely ground insecticide with a diluent (eg. fine talc or clay particles). The mixture may be prepared by coating a diluent with insecticide or by milling the two components together in a ball mill.
Advantages of dusts formulations include:
- Fine dusts usually spread well in these hidden areas, reaching places where pests hide, like complex equipment (eg. behind dishwashers, refrigerator motors, etc), cracks and crevices in walls.
- They are practical in situations where wet sprays can’t be used due to safety concerns or for aesthetic reasons.
Disadvantages of dusts formulations include:
- They can leave noticeable and unattractive residues if not applied carefully.
- These residues are not firmly fixed and can easily be blown away or wiped off.
- It is important not to use them above ground level if there is a risk of contaminating food, utensils, or similar items.
Insecticidal dusts should only be used in areas where they will stay fairly dry. Some types contain carbamate and synthetic pyrethroid insecticides.
Aerosols
Aerosols are handy systems that, when you press the nozzle or trigger, release a spray into the air containing insecticide droplets. There are two main types of aerosol systems:
- ‘Pressure pack’ aerosol
- High-pressure liquid carbon dioxide aerosol.
Pressure pack aerosols
These are often called ‘pressurised aerosol containers’. They typically contain insecticides (often safe, or sometimes with a synergist), an oil solvent, and a propellant, usually a type of hydrocarbon. The container has a dip tube that connects to the valve at the top and remains open at the bottom. Normally, pressure keeps the propellant in the liquid state, mixing it with the other components. The pressure is released when the valve is pressed, and the liquid mixture travels up the dip tube and exits the nozzle. Then the propellant evaporates, breaking the mixture into fine droplets.
Initially, aerosol sprays were only used to control flying insects like flies and mosquitoes. But now, thanks to improvements in nozzle designs, droplet size, and active constituents, aerosols can be used in various ways:
- Surface treatment – larger droplets are used to apply residual insecticides.
- Crack and crevice treatment:
- Using a remote push button nozzle connected to the can with a flexible hose or extension tube.
- Using a small plastic extension tube attached to the standard nozzle on the can.
- Total release or ‘one shot’ – the can is placed in a room or void and when activated, releases all its contents at once.
- Automatic dispensers – these are mounted on walls around a building to release small amounts of insecticide at set intervals.
For technicians, pressure pack aerosols are a very convenient way to apply insecticides without needing to mix anything on-site. This method is especially useful for reaching into cracks and crevices effectively, making it great for using flushing agents and for regular pest control tasks.
High-pressure liquid carbon dioxide-propelled aerosol system
When in use, a high-pressure gun and hose are attached to the valve. Operating the gun allows the liquid mixture to escape up the dip tube, along the hose, and out through the gun nozzle. At this point, the carbon dioxide quickly boils off, breaking the insecticide into very tiny droplets.
This system is mainly used for spraying large areas and reaching cracks and crevices to control household pests effectively. It operates at high pressure, producing tiny droplets for thorough distribution of the insecticide. In warehouses or buildings, multiple nozzle automatic systems can be installed for regular space-spray treatments.
Other Formulations
Insecticidal lacquer
The insecticide (1-4%) is mixed with a resin formula so that when it is painted onto surfaces, small crystals of insecticide keep appearing for months. This material is applied by painting or spraying onto surfaces and can stay effective for several months.
Smoke generators
The insecticide is combined with a combined with a pyrotechnic substance (like sodium chlorate) and a burnable ‘fuel’ (eg sugar). When the mixture is ignited, the insecticide is vaporised. Smoker generators are suitable only for enclosed spaces.
Baits
The insecticide mixed with an attractant in suitable amounts. Different forms are available including gels, pastes, and granules. Some come in bait stations ready to be placed, while others are in cartridges used with an application gun.
Bait technology has significantly improved, offering a variety of products for controlling urban pestslike cockroaches, ants, and termites. Bait formulations are expected to become more important in urban pest management.
Granules
Insecticide is applied to glay granules, usually in similar in size to sugar granule, and the spread where needed. Granules are mainly used in crop pest control and are effective for managing various insects that live in the soil.
ULV (ultra low volume) formulations
Some insecticides, which are oily liquids on their own, might be provided either neat or in a small quantity of oil solvent for ULV spraying. ULV-dispensing equipment breaks down the insecticide into extremely small particles, requiring only small amounts of concentrated insecticide.
Impregnated resin strips
The highly volatile insecticide dichlorvos can be embedded into resin strips. When placed in an enclosed space, these strips release toxic vapours that kill insects by inhalation.
Choice of formulations
When deciding which formulation to use for pest control, several factors will likely be considered:
Pest to be controlled. There are various registered products and formulations available for different uses, and it is important for the technician to choose the right one for the job.
Calculation of spray mixes
Convenience of use. Some technicians find it easier to use premeasured sachets containing wettable powders or water-soluble bags instead of measuring out liquid emulsifiable concentrate from a drum or bottle.
Application equipment available. If an operator does not have a dust dispenser, they might spray a mist into a roof cavity. However, if they have a power dust applicator, they can avoid the risk of misting in the roof space and instead apply a consistent, thin layer of dust evenly.
Nature of surfaces to be treated. When applying surface sprays to control crawling insects that will come into contact with the insecticide later on, the type of surface is important to consider. Emulsion, which is all liquid, can be absorbed by porous surfaces like unpainted wood or brickwood. On the other hand, wettable powders, suspension concentrates, and micro-encapsulated insecticides deposit solid particles on the surface, making them available for insects to pick up.
Pest habits and habitats
- When pests are contained and protected, like timber borers in furniture, the best treatment may be fumigation. Fuumigant gas penetrates the wood to kill the pests.
- For insect pests that hide in cracks and crevices, such as cockroaches, there are various treatment options.
- A non-residual flushing chemical like pyrethrins;
- A residual insecticide ( eg. wettable powder, suspension concentrate; micro-encapsulated, or emulsifiable concentrate);
- A residual dust insecticide;
- Gel bait or paste;
- A combination of these methods.
Price. The price of insecticide formulations varies depending on manufacturing costs. When comparing liquid concentrate products, operators should consider the total cost of spraying, including application expenses, rather than just the cost per sachet or litre of concentrate. Labour costs for application should also be taken into account.
Hazard minimisation
- When insect hiding spots are near electrical switches, wiring, or appliances, it is important to avoid using wet sprays for safety reasons.
- In places where animals are kept, such as pet shops or some homes, sprays and dusts may not be suitable. Instead, strategically placed baits and traps may be a better option.
- If areas to be treated are regularly occupied by people, space-spray systems are not suitable. Safer alternatives could be low volatility, low toxicity wettable powders, suspension concentrates, micro-encapsulated insecticides, or baits.
- Nowadays, client concerns and preferences are influencing technician’s choices of insecticides and formulations.
- It’s crucial to minimise the risk of unintended contamination in non-target areas (eg. from run-off). The selection of insecticide, formulation, and application equipment should prioritise the safety of the pest control operator, residents or workers in and around treated areas, pets, other animals, and the environment as a whole.
Regulatory obligations. Product labels contain important information about how well the product works and how to use it safely. Many factors affect which insecticide formulations are chosen. Users should carefully read product labels to make sure the chosen product is right for the intended use. Then, regardless of the product chosen users must:
- Read the label before opening it.
- Use the product exactly as directed on the label.