[Formulations Primer] Insecticide Basics: Formulations

Choosing a less-than-appropriate formulation can limit a pest management program’s effectiveness even if proper inspections are conducted and the most appropriate sites are selected for treatment. Here’s a review of the industry’s most widely used formulations — and the best situations in which to use them.
 

Insecticides are only rarely available to PMPs as technical grade active ingredients. Instead, the technical grade material is first combined with inert ingredients in a process known as formulation. The result of the formulation process is a product that can be purchased and used by a PMP. Inert ingredients improve the safety, handling, storage and efficacy of the final product’s active ingredient. They can:

• enhance product safety by reducing the potential for exposure;

• make the product easier to handle, mix and store;

• extend the shelf-life and stability of the product;

• keep the active ingredient suspended and dispersed in water (many active ingredients are not water soluble); and,

• extend the longevity of treatment and improve overall product performance.

Formulation choice is an important component of pest management programs. Choosing a less-than-appropriate formulation can limit a pest management program’s effectiveness even if proper inspections are conducted and the most appropriate site(s) are selected for treatment. A pesticide molecule’s availability can be lessened by using a formulation that inadvertently prevents the active ingredient from reaching the target treatment site and/or is unavailable to the target pest even when encountered.

Product and formulation choices by pesticide applicators have a variety of justifications including cost, product reputation, customer demand and product perception, availability, manufacturer support, safety and environmental considerations, ease of handling, storage and disposal, presence/absence of a particular active ingredient, liability perceptions, etc. As important as these reasons are, product efficacy should be of paramount importance when considering and choosing one formulation type over another. Choosing the most appropriate formulation is a complex process. The following discussion, therefore, should be referenced solely for technical reasons/justifications for formulation choice. All non-technical considerations are excluded.

Bait Formulations. Baits must be eaten by the target pest — typically rodents, termites, ants, cockroaches and other miscellaneous pests (see Figure 1 on page 83). Baits are comprised of an active ingredient incorporated into a palatable, if not preferred, food source. Bait products usually contain inert ingredients (e.g., preservatives, thickeners, gels and fillers) intended to stabilize and enhance the shelf life and palatability of the bait. Logically, it is important that bait ingredients (actives and inerts) not be a deterrent to feeding.

Baits are most commonly formulated as ready-to-use liquids, gels, pastes, granules, dusts, stations, pellets and blocks. Depending on the product’s label, baits can be used both indoors and outdoors, are generally target-specific and considered environmentally friendly because only small amounts of active ingredient are delivered, usually from a point source. Because baits must be eaten, it is important to keep them away from non-target organisms.

To facilitate bait consumption, (a) the active ingredient nor any other part of the bait should be a feeding deterrent and (b) the food source should be palatable (perhaps even preferred) by the target pest. In addition, for social insect pests (especially ants) it is important that the active ingredient be slow acting. Ants and termites share food with their colony mates in a social behavior known as trophallaxis (see Figure 2 on page 83). Trophallaxis results in active ingredient distribution throughout social insect colonies. It is, therefore, important that the active ingredient be slow acting over a range of concentrations in order to provide sufficient time for toxicant distribution among nestmates. Fast-acting active ingredients or excessively high concentrations of the active ingredient may too quickly impair a social insect’s ability to engage in trophallaxis, thereby rendering the bait less effective.

Granular Formulations. Granular products are formed by impregnating or coating a small granule of an inert carrier (such as clay) with an active ingredient and various inert ingredients designed to enhance the performance of the product. Granular products are a ready-to-use formulation typically applied around the perimeter of the structure to mulch, leaf litter, lawns, thick vegetation, etc., to control a variety of crawling pests. After application, the insecticide must be released from the granule by allowing water to dissolve it. Thus, granular products often require the presence or application of some form of moisture following application. With each successive rain, until the granule dissolves completely, insecticide is released into the treated area. Because of this requirement, granular formulations may be less effective when used during periods of drought. Like liquid sprays, granular products act by contact (direct kill) and perhaps by keeping foraging pests out of treated areas (deterrency).

It should be noted that pests do not eat granular formulations, as they do granular baits. A granular formulation is never bait, but bait can be in the form of a granule. For example, two products widely used for fire ant control are Advion (0.045% indoxacarb) and TopChoice (0.0143% fipronil). While both are small granules, the manner in which fire ants are killed is different (see Figure 3 on page 83). Advion is bait and must be eaten by the ants. TopChoice is a true granular formulation. After application, the TopChoice granules degrade, leaving behind a residue of fipronil in the treated area. As ants crawl across the residual, they acquire a lethal dose of fipronil and are killed by contact. Fire ants do not eat TopChoice granules.

The primary technical advantages of granular products are their weight and lengthy residual/slow release. The weight of granular products allows them to reach areas that liquid spray treatments normally would not. Liquid sprays do not penetrate deep into thick vegetation, mulch, leaf litter and ground covers (such as ivy). Because granules are heavy, they fall through thick vegetation to the soil surface and thatch layer below, thereby providing treatment to those hard-to-reach areas where crawling pests live (see Figure 4 on page 83).

Dust Formulations. Dust products have the consistency, look and feel of powder, are ready to use when purchased and are applied dry. Dusts are comprised of microscopic particles of active ingredient often mixed with microscopic particles of an inert carrier such as talc, clay or volcanic ash. The carrier also serves to dilute the active ingredient. In some cases, however, dusts are applied undiluted as technical grade active ingredient (e.g., some silica gels, diatomaceous earth, boric acid).

Many users make the mistake of over-applying dust. Dust should be applied so that a very light film settles on treated surfaces. Ideally, the quantity of dust applied should be only slightly visible in comparison to areas not treated (see Figure 5 on page 83). In some cases, over application can repel target pests, rendering the dust less effective or even ineffective.

Dusts should be used only in voids created by elements of construction (e.g., behind brick veneer, drywall, electrical switch-plates and sockets, synthetic stucco and in attic soffits). Dust should never be applied where or when it might be later encountered by non-target organisms. Because dusts become airborne easily, misapplication or mishandling can result in accidental inhalation. Therefore, it is important for applicators to always wear a protective mask and eye protection when applying any dust formulation.

Aerosols. Aerosols are an effective means of delivering insecticides, usually contact insecticides, into cracks and crevices where pests live. Aerosols kill by contact, unlike fumigants, which must be breathed by the target insect. Aerosols are comprised of an active ingredient(s) dissolved or suspended in a solvent that is then combined with liquefied or compressed gas. The gas serves as a propellant. The contents of aerosol cans are held under high pressure of 120 PSI or greater. When pressure is released (usually by depressing a button known as the actuator), the insecticide-solvent mixture passes through a valve and is broken into microscopic droplets. The solvent evaporates quickly, leaving the lightweight droplets suspended and floating in the air. By varying the characteristics of the nozzle design, the size of the droplet can be altered. Fine droplets stay airborne longer, while larger droplets settle more quickly. Because aerosol droplets can be made microscopic, they can be easily breathed. Caution should be used when using aerosols to avoid their accidental inhalation.

Fumigants. Fumigants are pesticides that are gaseous, applied undiluted as technical grade material and used solely for the treatment of existing pest infestations. Fumigants are simple molecules with low vapor pressures that permit volatilization and subsequent vapor-phase toxicity. They must be breathed by the target pest. Fumigants penetrate anywhere air penetrates — e.g., voids where pests live and breed, agricultural commodities such as grains, cracks and crevices and insect galleries in wood. When used properly, fumigants can eliminate an infestation of pests within a confined area. Fumigations are appropriate when the target pest is inaccessible to conventional treatments, when the infestation is so widespread that its distribution cannot be easily delineated or treated or when nothing short of pest elimination can be tolerated. Fumigations are often required to meet various regulatory standards regarding transport of products (commonly agricultural in nature) that might inadvertently introduce or spread a harmful pest species.

The most commonly used structural fumigant is sulfuryl fluoride (Vikane Gas Fumigant; Dow AgroSciences, Indianapolis, Ind.; and Zythor, Ensystex II, Fayetteville, N.C.). Sulfuryl fluoride has a number of attributes that make it an excellent structural fumigant. For example, it readily penetrates fumigated items and then dissipates from them when the fumigation is complete, is not flammable, explosive or corrosive, does not penetrate human skin, is stable both in and outside the storage tank, readily volatilizes when released from the tank, has low water solubility and produces no postfumigation odor. Sulfuryl fluoride is sold as a liquid contained in large pressurized tanks containing 125-130 pounds of technical grade active ingredient (more than 99 percent). When released from the tank, the liquid sulfuryl fluoride immediately vaporizes. Because sulfuryl fluoride is colorless and odorless, it is released into residential and commercial structures following application of chloropicrin (tear gas) as a warning agent to persons who might try to enter the fumigation site.

The required dosage of sulfuryl fluoride is pest-dependent and can be obtained directly from the product’s label. To determine dosage, the use of sulfuryl fluoride requires specific calculation equipment, which is obtained from the product’s manufacturer. Dosage is dependent upon: (a) concentration of fumigant in the confined space, (b) the amount of time (hours) that the fumigant is held at that concentration and (c) the temperature at the fumigation site. A tarpaulin must be placed over the structure or potential leak sites sealed with tape and/or a polyethylene sheet (e.g., seals around doors and windows) to achieve a desired concentration of gas within a confined space (see Figure 6 on page 84). The quality of the seal in large part determines the length of the fumigation process.

As the temperature increases, the required dosage needed to kill the target insect pest decreases. This requirement is not necessary for warm-blooded pests, such as rodents. Insects are cold-blooded, meaning that their activity is directly dependent upon the environmental temperature at which they are living — i.e., as the temperature increases, so too does the respiration rate of insects. Because fumigants enter the insect body by inhalation, an increased respiration rate in the target pest enhances its inhalation of fumigant, thus reducing the dosage needed to kill the pest.

Fumigants have limitations. Generally, insect eggs are less susceptible to fumigants than are adult and immature stages (larvae and pupae). However, label-required dosage rates compensate for differences in susceptibility among life stages of the target pest(s). Physical attributes of fumigated wood that may lessen the penetration of gas include excessively wet wood (e.g., sulfuryl fluoride has very low water solubility), large diameter logs and the presence of finishes designed to seal wood pores. Although a properly conducted fumigation can eliminate an existing insect infestation, fumigants leave no residual chemical once the building is aerated and cleared of gas. Depending upon the customer’s point of view, this can be viewed as either a negative (i.e., there is no residual chemical to protect against new infestations) or a positive (i.e., there is no chemical residue remaining on any treated surface).

The use and handling of fumigants by PMPs requires special training, licensing and ongoing education. The University of Florida publishes an excellent resource ("The Florida Fumigation Manual," www.ifasbooks.ufl.edu) for those who conduct structural fumigations.

Liquid Spray Formulations. Formulations commonly applied as liquid sprays are emulsifiable concentrates (abbreviated as EC), wettable powders (WP), microcaps (ME [microencapsulates] or CS [capsule suspensions]) and suspension concentrates (SC). These formulations must be diluted with water before they can be applied.

Emulsifiables are formulations that allow a water-insoluble insecticide to be suspended in water. Water and oil do not mix — that is, unless an emulsifying agent is added. When an emulsifier is added to a mixture of oil and water, microscopic droplets of oil are formed that disperse throughout the water. The resultant milky-white mixture is referred to as an emulsion.

Contact insecticides must be hydrophobic (insoluble in water) in order to penetrate the insect cuticle and/or interact with target sites. Although insoluble in water, most insecticides are soluble in oil or another solvent. To form an insecticide-active emulsion, the insecticide is dissolved in the solvent. When the emulsifier is then added, the resulting milky-white emulsion contains microscopic droplets of insecticide-impregnated solvent that become dispersed evenly throughout the water, as described in the previous paragraph. This resultant formulation can then be sprayed. The droplets in emulsifiable formulations do not settle like suspensions and, therefore, require minimal agitation in comparison to formulations that are suspensions (wettable powders, microencapsulates, suspension concentrates). Because emulsifiables readily absorb into skin, appropriate precautions should be used to minimize contact.

Wettable powder formulations are created by impregnating or coating a microscopic particle of an inert carrier (e.g., adsorptive clay, talc, etc.) with insecticide and various inert ingredients to enhance the wetting, spreading and dispersing characteristics of the powder. The inert ingredients (wetting agents) allow the dry powder to evenly disperse in and mix with water without clumping or caking. Because wettable powders are true suspensions, constant agitation is required to keep the powder suspended in water (see Figures 7 and 8 on page 84). Wettable powders do not readily absorb into skin, but care should be taken when using this formulation to avoid accidental inhalation.

Suspension concentrates can be considered wettable powders that have been packaged in liquid formulation. They consist of very small crystals of technical grade insecticide mixed with an extremely fine, inert dust, a small amount of water and various other inert ingredients. The other inert ingredients enhance the dispersion and mixing characteristics of the formulation when diluted with water. Because suspension concentrates settle out of suspension, they require constant agitation.

Microencapsulated products are formed by encapsulating an insecticide in a microscopic, round, plastic capsule. The capsules are mixed with inert ingredients — dispersants, wetting agents, etc. — to keep them from clumping and to help the mixture flow more readily. The inert ingredients also facilitate storage and dispersion when diluted in water.

The capsule’s wall thickness determines the release rate of the insecticide to the outside environment. The insecticide seeps through the capsule’s wall and coats the outside of the capsule. As the insecticide disappears (degradation, evaporation, etc.) additional insecticide inside the capsule continues to coat the capsule surface. This process maintains a capsule that is constantly coated with a thin film of insecticide. The manufacturer can change the characteristics of the capsule wall to slow (or accelerate) the release rate of the chemical from inside the capsule, thus, altering the residual life of the treatment. Changing the characteristics of the capsule can alter the product’s odor (slower release rates result in less smell); protect the chemical from environmental degradation; influence the rate of kill by the insecticide (faster release rates mean a faster rate of kill); and reduce exposure to non-target organisms. Because microcaps settle out of suspension, constant agitation is required.

Daniel Suiter, Ph.D., is with the Department of Entomology, University of Georgia, Griffin. Michael Scharf is with the Department of Entomology, Purdue University, West Lafayette, Ind.
 

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New Termiticide Formulation
Expands Use Patterns

General use insecticides aren’t the only products that undergo formulation enhancements to address ever-changing market needs, expand use patterns or enhance efficacy. Termiticide formulations also are evaluated on a regular basis by basic manufacturers. A prime example is a new product from BASF Pest Control Solutions, Termidor DRY, featuring its patented Microllose-based formulation.

More than just an inert carrier, Microllose is a unique cellulose food source – formulated with 0.5 percent fipronil – that is even more appetizing to termites than wood, according to BASF. "Not only does Microllose act as a carrier of Termidor, but it also can serve as an alternate diet component," says Tom Nishimura, BASF technical services specialist. "It meets the dietary requirements of termites."

In addition to serving as a viable food source for both drywood and subterranean termites, the microscopic particles found in Termidor DRY readily adhere to termites, resulting in rapid distribution throughout the colony. Following treatment, when these "carriers" come in contact with other termites in the colony, the toxicant is shared during grooming or other interaction, resulting in the Termidor "Transfer Effect."

Termidor DRY was developed for use on gallery treatments inside structures and on new "off-structure" treatment sites, including trees, utility poles, fencing, decking, railroad trestles, piers, beams and other structural or landscape timbers. The product comes in small, prepackaged, ready-to-use vials, which generally treat two to three average-sized houses depending on termite infestation.

"Pest management professionals can experience proven Termidor efficacy and reliability with Termidor DRY in locations Termidor termiticide/insecticide has never been before," said Ryan Weber, product manager for BASF. "The Termidor DRY formulation, applicator, method and uses are significant opportunities for the industry."

Visit http://pestcontrol.basf.us/TermidorDRY to see and learn more, or find BASF Pest Control Solutions at www.Facebook.com/BASFTermidorPestControl.

Termidor DRY is now available. Contact your BASF Sales Specialist for more information. — BASF Pest Control Solutions
 

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New Formulation Makes Big Difference

You might say Jim Nase knows the pest control business inside and out. A 33-year industry veteran, Nase is both service manager and technical manager for Moyer Pest Control in Souderton, Pa. He’s been with the company for 15 of the 16 years the pest division has existed.

"In this area, we target certain insect pests for each round of our Exterior Guard Service, which provides four rounds of treatments from March through October," says Nase, who also serves on the technical committee for Copesan. "We battle odorous house ants in Round One; spiders, bees and wasps in Round Two; ants again in Round Three and boxelders and stink bugs in Round Four." Nase rotates products through each of the cycles, using a combination of liquids and baits.

A spike in bed bug problems in recent years caused Nase to begin looking for new form-ulations to use for improved results. Although Moyer hasn’t seen the bed bug explosion experienced in other areas of the country, "We are always on the lookout for improvements in product technology," explains Nase.

Testing a New Product. When Nase agreed to be a beta tester for Transport Mikron insecticide, a brand new insecticide formulation from FMC Professional Solutions, he first began using it in the company’s Round Two — mostly for spiders, springtails, carpenter bees and wasps.

"Transport GHP is an awesome product for those pests, but — as with many wettable powder or microencapsulate formulations — we sometimes have visible residue issues, where technicians apply it to dark surfaces," explains Nase. "If technicians leave it in the tank, a wettable powder formulation settles down quickly. The next time they use it, they might get a higher concentration than what they need."

The new formulation is a combination of acetamiprid and bifenthrin, the same active ingredients as Transport GHP. But Transport Mikron is a microemulsion formulation that allows for extremely even distribution of active ingredient throughout a finished solution. The microemulsion stays in suspension for extended periods of time — even after periods of non-use. In addition, it is an almost clear formulation, which reduces the visible effects of an application.

"When we used Mikron, we still had the quick knockdown and great residual, but we had no staining issues — zero," notes Nase. "It is applied the same way, as a perimeter treatment. The label says 10 feet — so it could be 3 feet up the wall and 7 feet out. But Transport Mikron stays in suspension — it’s an amazing thing to see."

In addition, Transport Mikron has an extremely small particle size, FMC reports. This allows the material to quickly penetrate the insect’s cuticle, providing quick knockdown and kill.

Currently, Nase is testing Transport Mikron for bed bug control. He’s used it for bedframe and crack-and-crevice treatments and around the carpet areas. "We’ve done 10 applications so far and it’s looking very, very good," adds Nase. "We’ve tried Mikron for bed bugs in many different settings — not just homes — and we are extremely encouraged by our results. When technicians come back to the office and say they want to keep using a product, that’s always a good sign." — FMC Professional Solutions
 

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iCAP Technology: A Unique Microencapsulation Process

Years of research and development went into creating iCAP technology, a proprietary manufacturing process used to create Demand CS and Demand EZ insecticides from Syngenta. This unique microencapsulation process first encapsulates the active ingredient in a spongy polymer shell. Then a second shell is applied to further protect the active ingredient from environmental effects. This dual-wall construction forms cross-links around the active for capsule strength and an extended release rate of 90 days. To achieve this length of control, the formulation is developed with a mix of capsule size ranging from 5 to 22 microns. The smaller capsules release the active more quickly while the larger capsules work more slowly to further extend residual control.

"The microcap produced through iCAP technology is strong enough to maintain control between bi-monthly and quarterly service cycles, lessening the chance that a PMP will be called back to retreat," said Bob Cartwright, technical manager, Syngenta. "We’ve tested other microcaps and seen them break down after 30 days of sun exposure while Demand still controls pests up to 90 days after treatment. That power comes from the technology." — Syngenta