Nicole Tyzack from Syngenta reports on Dr Bill Robinson’s ‘Application and Equipment’ presentation.
Recently Dr William ‘Bill’ Robinson visited Australia and New Zealand where he shared his vast knowledge and intel with groups from the industry. Bill Robinson has a B.A., M.A. and Ph.D. with majors in biology and entomology and minors in geology, meteorology and botany. He was a Professor and Director of the Urban Pest Control Research Centre at Virginia Polytechnic Institute and State University for about 30 years. For 16 years he was a Visiting Professor and Director of the Urban Entomology Centre at Zhejiang Agricultural University in Hangzhou, China.
Along with 20 graduate and post-doctoral students he has conducted and published research on cockroaches, carpenter ants, dust mites, fleas, flies (phorids), termites, wood-infesting beetles, insecticide resistance, wood protection, insecticide application technology and turf pests. He has written several books on urban entomology and a series of training manuals for service technicians. He has been technical director of B&G Equipment for 15 years.
One of the workshops he ran was around ‘Application and Equipment’. What follows is an excerpt of some of what was covered.
The efficacy of an insecticide treatment depends on the combination of the insecticide’s active ingredient, formulation and application. These are the main factors that influence how long the application remains effective. It is also important to understand the habits of the pest, such as movement and foraging. The objective is to treat substrates that will be contacted by the pest when it is in or leaves a harbourage. When all these parts are in the proper sequence, control is achieved.
So, control is based on contact of the pest with an insecticide, the efficacy of the insecticide is based on application, and the efficiency of application is based on equipment. Modern insecticides have dramatically changed professional pest control. They are effective, selective and used at low concentrations. The challenge for the industry is to match the insecticides with the most efficient application methods and tools. The efficacy of liquid, dust or bait depends on precision delivery to the pest or substrate.
Basics of insecticide application
The most common formulations are microencapsulated (ME, MC), wettable powder (WP), suspension concentrate (SC) and dust (D). These are designed specifically for the active ingredient and how it will be used. Some active ingredients are available in more than one formulation. For example, an SC may be suitable for soil applications, but an ME is better for surface treatments.
The formulation can influence the long-term activity of an insecticide by how it forms a residue and how the target pest is exposed to it. Foam and aerosol sprays are formats for delivering liquid insecticide. Foam can improve the spread of liquid on the surface of soil or in a wall void.
An aerosol spreads a liquid in the form of droplets in a substrate, which is an air space, to improve contact with flying insects.
Substrate and residue
Spraying a surface may seem to be a simple process, but there is a lot to consider if the treatment is to be effective and cost efficient. The objective is to apply droplets of insecticide to establish a surface residue that will be contacted by the target pest. While the equipment and the spray droplets remain the same, the composition and surface of the substrate can be significantly different.
The time between an insecticide application and contact by the target pest is important in achieving control. The residual toxicity of insecticide on exposed surfaces is limited by environmental conditions or other events that remove the residue, and by the insecticide itself. Some formulations (like the microencapsulation of Demand Insecticide or the suspension concentrate of Altriset Termiticide) stay effective longer than others.
Time is a factor for indoor applications. For flea control, spraying indoor carpeting is a typical method of control. However, it can take a few days for the liquid insecticide to move down the fibres to the base of the carpet where it will be contacted by larvae. During this time the insecticide may be exposed to damaging ultraviolet light passing through windows, or it may be damaged or disturbed by foot traffic or vacuuming. The initial residue may be less effective by the time adult fleas emerge at the base of the carpet and crawl to the surface.
The residues of wood-protection insecticides are expected to remain effective for long periods. Liquid and foam applications to structural wood produce a residue at, and immediately below, the surface. The surface residue will degrade within weeks of application, especially when the treated wood is in an attic or a crawlspace. Below the surface, where the liquid moved during and after treatment, there is a stable residue which is protected from environmental conditions and may last for years.
The efficacy of an application is also determined by the target pest and its habits. The pads on the feet of insects contact the surface during walking and climbing. The movement of the insect’s legs and the spines on its feet can help dislodge residue on the surface, which can be picked up by the tarsal pads. Residue on the pad enters the body directly or is transferred to the mouth when the legs are groomed.
Insects that forage at night, such as cockroaches and bed bugs, remain in narrow harbourages during the day. This activity pattern limits their exposure to insecticide residue unless harbourages and surrounding surfaces are treated. Adult bed bugs leave their harbourage to feed only every three to four days, and they may not have to travel far to find a host.
German cockroach females carrying an egg case leave a harbourage about every five days to eat and drink. These foraging habits influence the efficacy of spray applications.
Insects and other pests die within hours or days after exposure to an insecticide, whether by being directly sprayed, contacting a dry residue, or eating toxic bait.
For ants to carry bait back to the nest, the concentration of active ingredient has to be low so that these individuals are not killed. But the concentration must be enough so that a lethal amount accumulates in the body of the queen and larvae that are fed by the workers.
Cockroach gel baits lose about half their moisture content in the first two days after application. This essentially doubles the concentration of active ingredient in the bait.
The primary objective of liquid insecticide application to surfaces is to kill insects that crawl on those surfaces. The droplets from the spray pattern create a dry residue on treated surfaces. Insects and other pests then pick up a lethal dose when they walk on the residue. Creating an effective residue depends on using a fan-spray nozzle at optimum pressure and overlapping the spray pattern to achieve complete coverage.
Application with a crack-and-crevice straw creates a residue in narrow spaces with a stream of liquid.
Basics of surface application
A coarse-fan spray is used to treat indoor and outdoor surfaces. The large droplets in this spray pattern do not fragment into smaller ones when they hit the surface, so they are less likely to drift during treatment.
The most effective and cost-efficient residue consists of droplets. Spraying to completely wet the surface does not increase control, but increases cost because insecticide and treatment time are wasted. Objective of a surface application is to create a lethal residue.
The effectiveness of liquid insecticide is not based on the amount applied, but on where and how it is applied.
Crack-and-crevice application delivers insecticide into narrow openings and voids. The residue controls crawling pests that use these sites as harbourage or as travel routes between food and nest. This application increases control and reduces insecticide exposure to people and pets. The residues remain effective for long periods because they are protected from environmental conditions.
Crack-and-crevice treatment is effective because it contacts 90% of the infestation 90% of the time.
This is just a section of the presentation and in his manual there is greater detail and information where you can build your understanding of the intricacies of application. As Dr Robinson says in the introduction of his latest manual – The Service Technician’s Application And Equipment Manual, A Practical Guide for Pest Control Professionals – insecticide application and equipment must be managed to have a successful business, but you can’t manage what you don’t understand.
The next generation of professional pest managers will know the methods and the tools of application, and utilise that knowledge to manage the costs of using them.
Nicole Tyzack, Syngenta