INSECTICIDE FORMULATIONS
Residual Insecticides
Suspo-Emulsions (SE) Suspo-emulsions combine the residuality of suspension concentrates, with the speed of effect of ‘oil-in- water’ emulsions (EW’s). They also incorporate an additional active ingredient, often a specific knockdown agent, in the liquid phase. Offering good residual control with fast flushing and knockdown. 3. Other Liquid Concentrates Some liquid concentrates do not contain particulates so that when sprayed onto porous surfaces the formulation is absorbed and may not be as readily available for the target pest to contact, when compared to the residual liquid concentrates on the previous pages. These formulations are more suitable for sealed surfaces such as painted wood, metal or tiles. Formulations of this type include: - Micro Emulsions - Oil in Water Emulsions - Emulsifiable Concentrates Micro-Emulsions (ME) This type of formulation is manufactured by a process sometimes referred to as nano-technology. It carries the active ingredient as extremely small droplets, in a high surfactant liquid phase. Micro-emulsion concentrates have a slightly ‘soapy smell’ and dilute in water to provide a clear, stable, ready-for-use liquid. The small droplets of active substance provide a very large number of point sources of contact that make it difficult for the target insect to avoid on a treated surface. The high loading of surfactants also facilitates the rapid penetration of the insect’s cuticle. This formulation type provides excellent residual control on non-porous surfaces such as metal and ceramic tiles, but is not as effective on sorbtive surfaces when compared with suspension concentrates and wettable powders. Oil in Water Emulsions (EW) In this formulation type the active ingredient is dissolved in a small quantity of oily solvent that is then dispersed in water to produce a stable milky emulsion. When compared to emulsifiable concentrates (EC), solvent incorporation is reduced by over 80%. Products also generally have less odour and a greatly reduced flammability risk. EW’s offer excellent residual control on non-sorbtive surfaces such as metal and ceramic tiles, but are not as effective on sorbtive surfaces when compared with suspension concentrates and wettable powders.
Emulsifiable Concentrates (EC) The formulation of an active ingredient as an emulsifiable concentrate (EC) is still common, as this type of formulation is relatively simple to manufacture. An EC contains the active ingredient, a solvent and an emulsifier system that allows the formulation to be mixed with water to form a stable emulsion. As EC’s are solvent based, they often have more odour and may be less suitable for use in more sensitive areas. This formulation type can provide excellent residual control on non-sorbtive surfaces such as metal or ceramic tiles, but is not as effective on sorbtive surfaces compared to wettable powders and suspension concentrates. 4. Dustable Powders (DP) DP’s are very simple formulations where the active ingredient is mixed with a filler of small particle size together with anti-caking agents and adjuvants to produce a free-flowing product. There are no emulsifiers or surface-active agents and so DP’s are not miscible with water (unlike WP’s). These simple formulations are used to ‘dust’ an infested area and the target pest picks up a lethal dose as it walks through the dust. This formulation type leaves a very visible deposit so is only of use in certain situations. Products for dilution with (diesel) oil, kerosene or water and application through a ‘hot fogging’ or ‘cold aerosol’ (cold fogging) appliance. ‘Space treatment’ products are non- residual and are intended to completely infiltrate a body of air through which pests must move, typically applied during the early day-time for fly control, Space Treatment - Liquid Concentrates at dusk or evening for the control of most mosquitoes and midges, and, where permissible, into building voids, sewers and drains for the control of several species of cockroaches. Space Treatment - Ready-for-Use (RFU) As the name suggests these require no further dilution and can be applied through the normal range of fogging equipment or simple hand-held flit guns or sprayers. One advantage of solvent based RFU’s is that un-used product can be safely returned to the original pack until it is next needed, as the product will not decay.
The following insecticides are designed to rapidly control the target pest problem, and also to provide a period of sustained control from the residual effect of the insecticide. The duration of residual control will depend on the formulation type and where the product is being sprayed. Residual insecticides can be broken down into four distinct categories: 1. Wettable Powders 2. Particulate Liquid Concentrates 3. Other Liquid Concentrates 4. Dustable Powders 1. Wettable Powders (WP) Wettable powders are formulated to provide exceptional residual control. The active ingredient is mixed or adsorbed onto a mineral filler (depending whether the active is a liquid or solid at ambient temperatures). Dispersants and surface-active agents are added so that the formulation can be diluted, suspended, or dispersed in water for ease of application. This formulation type is especially useful for the treatment of highly absorbent surfaces such as brick, mud or some wood. After application, the active ingredient (and filler) is left on the surface as a microscopic, insecticidally active powder, that is readily picked up when an insect walks over it. 2. Particulate Liquid Concentrates A range of liquid concentrate formulations have been developed, and are designed to work most effectively in different situations:
- Suspension Concentrates - Suspo Emulsions
Suspension Concentrates (SC) In this formulation type an insecticide active ingredient is either milled to produce particles of a pre-determined size, or, if liquid, absorbed onto a filler which is then suspended in an aqueous matrix. This type of formulation has many of the benefits of a wettable powder, without some of the disadvantages. Suspension concentrates are less ‘dusty’, easier to dose, and easier to disperse in water than wettable powders. Like wettable powders, when suspension concentrates are sprayed onto a sorbtive surface, the insecticidal particles remain on the surface of the substrate where they are readily available to the target pest.
INSECT CONTROL | 101
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