Integrated Pest Management

IPM Manual for Structural Pests in British Columbia

Chapter 2: Preferred Pesticides

Learning Objectives

When you have completed this lesson, you should be able to:

1. State four criteria for a preferred pesticide.
2. For boron based pesticides, describe the mode of action, formulations and use.
3. For sorptive dusts (diatomaceous earth and silica gels), describe the mode of action, formulation and use.
4. For pyrethrins, describe the mode of action, formulations, safety and use.
5. For juvenile hormones, describe the mode of action, formulation and use.
6. For hydramethylnon (aminohydrazone), describe the mode of action, formulation and use.

What is a Preferred Pesticide?

The term 'preferred pesticide' is defined in this chapter and examples of preferred pesticides are described. These include:

• boron based pesticides,
• sorptive dusts,
• botanical pesticides,
• insect growth regulators,
• aminohydrazones (hydramethylnon), and
• extracts from micro-organisms.

Preferred pesticides in this manual are those that would be the first choice for use in a structural IPM program. This is because they are generally:

• least toxic to humans,
• have the lowest impact on non-target organisms,
• are most specific to the target species,
• present the least environmental risk during handling and disposal.

Some preferred pesticides are novel compounds, such as insect growth hormones and extracts from micro- organisms. Others, such as boric acid and diatomaceous earth, have been used to control pests for years. With the renewed interest in these compounds, they have been formulated into new and more effective products.

A preferred pesticide may or may not have a short residual effect. For example, formulations of the insect growth regulator, methoprene, provide up to 6 months of juvenile flea control. The sorptive dusts may remain effective for years inside a wall void if kept dry.

Other Pesticides

Preferred pesticides may not be suitable or available for all structural pest management programs. Sometimes, more toxic, less specific pesticides registered for structural pest control are appropriate choices in an IPM program. Conventional pesticides, such as organophosphorus and carbamate pesticides should be considered a short-term measure until other management methods, or more specific pesticides, are available to deal with the pest problem. The uses and safety concerns for these pesticides are discussed in Chapters 12 and 13 of this manual.

Examples of Preferred Pesticides

To choose an appropriate product and apply it effectively, it is important to understand how a pesticide works, the form it is sold in and the best way to apply it. This information is provided for each of the preferred pesticides described in this chapter.

Boron Based Pesticides (Borates, Boric Acid)

Boron is a chemical element. Borax, which contains boron, occurs naturally in the soil. Boric acid and other boron-containing compounds (generally referred to as borates) are manufactured from borax. Boric acid and borates are classified as preferred pesticides because they have relatively low toxicity to mammals and other vertebrates (including fish) and a low environmental impact.

Mode of Action

Boric acid and borates act as stomach poisons. When placed in wall voids or in cracks and crevices, the insects pick up the compound on their legs, antennae and bodies, then consume it when they groom themselves. When a boron based product is applied as a liquid to wood, wood-eating insects consume it directly. The mode of action of boron is not fully understood, but it seems that boron kills by disrupting the process of digestion. This causes the insect to starve.

Formulations

Boric acid is formulated as an insecticidal dust and as the toxicant in various formulations of insect baits. For cockroach control, it is available in a bait mixed with a food attractant (e.g., Blue Diamond M.R.F. 2000TM).

Borate solids (anhydrous disodium octaborate) are formulated into rigid rods (Impel® Rods) for insertion into holes drilled in wood.

A product containing water soluble borate salts (Tim-bor®) is registered for treatment of existing wood structures to control structural insect pests and fungi (availability has been a problem). The product can be applied as a powder, sprayed or painted on as a liquid solution or applied in a foam. It can be also be injected into wood and into wall voids or used as crack and crevice treatment in food handling areas.

Use

Boric acid is commonly used as an insecticide to kill ants, cockroaches, fleas and silverfish. In Canada it is registered as a crack and crevice treatment for flea control as well. In the U.S., boric acid dusts can be used to treat carpets, but it is not currently registered for this use in Canada. When boric acid is applied as a dust to control crawling insects it must be applied as a thin film because insects generally avoid thick layers of dust.

Most of the research done to date on boric acid formulations has been directed towards cockroach control. A boric acid bait, mixed with a food attractant, is widely available. It takes 5 to 10 days for cockroaches to die after eating boric acid. The slow-acting nature of boric acid means that cockroaches will be seen for at least two weeks after an application has been made. Boric acid does not repel cockroaches and so it has a greater likelihood of success than other insecticides.

Rods of solid borates are inserted into holes drilled into structural wood. If the wood becomes damp, the moisture in the wood causes the borates to diffuse from the rods into the wood. This protects the wood from insects and decay.

The soluble borates penetrate into wood to kill insects and fungi and protect the wood against further attack. Because borates do not decompose or change over time, they provide long-lasting protection. Borate solutions have been used for many years as green lumber dips by the lumber industry. A water soluble borate salt is now registered in Canada for control of carpenter ants, termites, wood boring beetles (including powderpost beetles) in structures.

Boric acid is formulated and used as a high percentage of active ingredient. If eaten in high doses it can be harmful. Therefore, it must be kept away from food, children and pets.

Boric acid dust should not be inhaled, as it can irritate the nose, throat and lungs. Boric acid and borates can be absorbed through skin lesions and burns. A protective dust mask, gloves and eye protection should be worn when applying boric acid dust.

Sorptive Dusts (Diatomaceous Earth, Silica Gels)

The most commonly used sorptive dusts are diatomaceous earth and silica gels. Sorptive dusts disrupt the oily layer on the cuticle of the insect. With their exterior water-proofing layer destroyed, insects dry up and die.

Diatomaceous Earth (Silicon Dioxide)

Diatomaceous earth is mined from fossil deposits in ancient seabeds. The word diatomaceous comes from diatom. Diatoms are tiny plants (phytoplankton) used as food by freshwater and marine animals. When diatoms die, they settle to the bottom of lakes and seas, where their skeletons form thick deposits. Over time, the deposits become fossilized into sedimentary layers. These are now mined and processed for use in industrial applications and as an insecticide.

Mode of Action

Contact with diatomaceous earth damages the water proofing layer on the surface of the insect. The microscopic, sharp particles scratch through the protective layer and may also act by absorbing the oils.

Formulations

Diatomaceous earth is sold as a dust. It is composed primarily of silicon dioxide, therefore the active ingredient on pest control product labels may list only silicon dioxide.

Glassified diatomaceous earth, used in swimming pool filters, should not be used for pest control. It is heated and ground to a smaller size than that used in pest control products and is hazardous when inhaled. Use only diatomaceous earth (silicon dioxide) that is registered for pest control.

Use

Diatomaceous earth works best on small, hairy insects with a thin cuticle. It is not as effective on cockroaches because they are large and have very oily cuticles. Beneficial insects, such as tiny parasitic wasps are particularly susceptible, therefore, it is generally not desirable to use this dust outdoors around garden plants.

Diatomaceous earth is safe for mammals to eat, but should not be inhaled. A respirator with a dust filter should be used when applying diatomaceous earth.

Silica Gel

Silica gel is made from naturally occurring silica, such as that found in sand.

Mode of Action

Silica gel works by absorbing the oils on the surface of an insect, causing it to dry out. Silica gel holds up to 3 times of its weight in oils and lipids.

Formulations

At this time, the only form of silica gel registered for use in Canada is silica aerogel formulated with pyrethrins (e.g., Drione®).

Silica gel, without additives, is non-toxic to humans and is safe for human consumption. It is used in the food industry in products such as antacids, baked goods and mayonnaise.

Use

Silica gel works best on small, hairy insects with a thin cuticle. As the humidity increases, the effectiveness of silica gel falls off. Silica gel is somewhat repellent to insects, therefore insects may only contact it for a short time.

Silica gel does not cause the lung disease silicosis, however, the dust should not be inhaled. Always use a respirator with a dust filter when applying silica gel.

Botanicals (Pyrethrins, Azadiractin)

Botanicals such as pyrethrins (from pyrethrum daisies) and azadiractins (from the neem tree) are pesticides derived from active compounds found in certain plants.

Pyrethrins

Pyrethrins are the active ingredients extracted from the pyrethrum daisy, Chrysanthemum cinerariaefolium. Pyrethrins are commonly used in structural pest control.

Mode of Action

Pyrethrins are nerve toxins. They work as a contact poison and cause quick paralysis in insects. Pyrethrins are known for their quick 'knockdown' effect and because they drive insects out of hiding places.

Many insects can detoxify pyrethrins and recover from exposure, therefore a synergist is often added to the formulation to help the pyrethrins work effectively. Piperonyl butoxide, a common synergist, is derived from sesame. It works by inhibiting the activity of enzymes in the insect that normally detoxify pesticides.

Formulations

Pyrethrins are available in a variety of concentrations and formulations including oil solutions, emulsions, aerosols, microencapsulated formulations and dusts.

Use

Structural pests most susceptible to pyrethrins are cockroaches, fleas, flies, mosquitoes and ants. Pyrethrins are widely used as an aerosol for flying insect control, occasionally in residual formulations (e.g., Ficam Plus®). The residual effect of the aerosol is usually short, although the product may last for some time in dark corners or other protected areas.

Pyrethrins can cause allergic effects in some people through skin contact or by inhalation. Where pyrethrins are applied, residents should be told to air out their homes before reentry. People should not reenter closed buildings until the extractor fans in the building have been in operation for a few hours.

Pyrethrum and pyrethrins are moderately toxic to mammals. They should not be inhaled and gloves should be worn when handling them as they can cause skin irritations. Protective equipment should always be worn when applying these compounds.

Pyrethrins can be toxic to cats, therefore only veterinary products that specifically list cats on the label should be used for flea control on cats. Pyrethrins are also highly toxic to fish.

Azadiractin (Neem)

Azadiractin is extracted from seeds of the neem tree (Azadirachta indica). The extract contains several active compounds that affect insects by repelling them, inhibiting feeding and disrupting their development. Azadiractin has very low toxicity to mammals and degrades rapidly in the environment. Although available for agriculture crops in the U.S., neem is not yet registered for use in Canada.

Insect Growth Regulators (Juvenile Hormones, Chitin Inhibitors)

Insect growth regulators are insect hormones, or their synthetic mimics. The growth process of insects is controlled by hormones. When they are exposed to these hormones at critical times during their life cycle it interferes with their normal development.

Mode of Action

The two categories of insect growth regulators are juvenile hormones (also called juvenile hormone analogs) and chitin inhibitors. Juvenile hormones prevent the target insect from reaching sexual maturity and completing its life cycle.

Chitin inhibitors prevent the production of chitin, which is the main ingredient of the insect exoskeleton (no chitin inhibitors are currently registered for structural pests in Canada).

Formulations

At this time, the only insect growth regulator available for structural pest control in Canada is the juvenile hormone methoprene (e.g., Precor®). This is currently registered for flea control. It controls juvenile fleas by preventing them from reaching maturity. Other juvenile hormones to watch for in the future are hydroprene, fenoxycarb and formulations of methoprene registered for control of other species.

A new insect growth regulator, lufenuron, is now available from veterinarians to control fleas on pets. This is given to pets monthly, as an oral medication. It does not affect adult fleas, but it stops the flea eggs from developing.

Use

Juvenile hormones are specific to particular groups of insects. They have low toxicity to vertebrates and are relatively safe for non-target insect groups.

When used for flea control, methoprene should be used with an adulticide as the juvenile hormone affects only the immature fleas.

Hydramethylnon (Aminohydrazone)

Hydramethylnon is a new, synthetic insecticide. It has low mammalian toxicity, is nonvolatile, and works well in baits.

Mode of Action

Hydramethylnon works by disrupting biochemical energy production in insects. This mode of action is unique among insecticides. It is a slow acting stomach poison, which must be eaten by the insect to be effective. Its effectiveness is partially a result of its slow acting nature. Insects consuming it in a bait live to return to the aggregations of other individuals (cockroaches) or colonies (ants) and have time to spread the toxicant.

Formulation

Hydramethylnon is available in small square plastic discs or bait stations (e.g., Maxforce®) for insect control.

Use

Hydramethylnon baits are registered for cockroach and ant control.

Extracts from Micro-organisms

There are potentially many different types of active compounds that may be extracted from naturally occurring micro-organisms.

Avermectins are one group that is extracted from a soil micro-organism, Streptomyces avermitilis. Avermectins are contact insecticides and stomach poisons. Avermectins have low mammalian toxicity and are highly effective in small amounts. A commercial crack and crevice product for cockroach control is now available in the U.S., though not yet in Canada.

Further Reading

Olkowski, W., S. Daar and H. Olkowski. 1991. Common-Sense Pest Control. The Taunton Press, Newtown, CT. 715 pp.

Quarles, W. 1992. Borate Provide Least-Toxic Wood Protection. IPM Practitioner. 14(7):1-11.

Quarles, W. and P.S. Winn. 1996. Diatomaceous Earth and Stored Products Pests. IPM Practitioner. 18(5-6):1-10.

Quarles, W. 1992. Silica Gel for Pest Control. IPM Practitioner. 14(10):1-11.