Safer Pest Control: Management of Wood-Destroying Insects
The historic district of New Orleans—like much of the rest of the city—is being ravaged by termites. The city is at particular risk because huge quantities of wood were installed underground to stabilize buildings when the city was built on the unstable Mississippi River delta, and because this is where Formosan termites, a particularly voracious species, first gained a foothold in the Continental U.S. Indeed, damage from termites is so severe in Louisiana that a statewide mandate for preservative-treated wood nearly made it into the books this year (see
Vol. 9, No. 3). But damage is by no means limited to Louisiana. In Hawaii, where Formosan termites have been a problem the longest in the U.S., building codes now require framing in steel or entirely out of preservative-treated wood—for a typical 2,000 ft2 (185 m2) house with chromated copper arsenate (CCA) treated wood, this means a total of about 250 pounds (113 kg) of the compound inside the building envelope. Termite damage in the U.S. today is estimated at $1 billion to $3 billion per year. At least a third of that damage is from the Formosan termite, which was accidentally introduced from China.
The nonstop flow of timber and other commodities worldwide is contributing to the introduction of exotic pests—from Formosan termites that are now established in 14 states and expected to threaten 80% of the U.S. building stock within 10 years, to the Asian longhorn beetle, which has recently been discovered in the Chicago area and could prove almost as damaging to our hardwood forests as the Chestnut blight. Global warming is also expected to extend ranges of existing pests northward. Spot infestations of termites have already been reported as far north as Toronto and Vancouver in Canada.
Coupled with the growing problem of insect pests is our ever-greater understanding of the health and environmental impacts of the chemicals we use to ward them off. Chlordane and heptachlor were removed from the market in the late 1980s. One of their primary replacements, Dursban, is being phased out. It has proven, not surprisingly, nearly impossible to develop a broadcast chemical that is a perfect killer of insects and safe for humans and the environment.
But while the bugs are multiplying, we’re getting smarter. A dramatic shift is occurring in pest control strategies—a shift that promises not only better control but far less damage to our health and the environment. The changes are so dramatic that a pest control operator from 20 years ago would scarcely recognize the business today. The recent change in name of the National Pest Control Association to the National Pest Management Association reflects this evolution. All this is good news—but it means that we as designers and builders have to be smarter in understanding pests and how to manage them. It’s no longer just a matter of treating a continuous band of soil around our buildings.
This article takes a look at the dramatic changes taking place in the management of wood-destroying insects, including termites, carpenter ants, and powderpost beetles. Primary emphasis is on termites because they are responsible for the vast majority of building structure damage and because their management strategies can involve not only the entire structure but the building lot as well. Two other important agents of structural damage—rodents and rot/mold—are left for another discussion.
Insect Pests 101
Termites, carpenter ants, and powderpost beetles eat wood or tunnel through it for nesting cavities, thus causing structural damage. The most common species of these insect pests are described in the table on right.
Termites eat wood—they all have tiny, single-celled protozoa in their intestines that digest cellulose. Worker termites are the only ones with the appropriate mouthparts to actually chew wood. Workers feed the soldiers, developing young, king, and queen. Colonies of termites can range from a few thousand—a drywood termite queen produces that number over her life of several years—to millions—a single subterranean queen can produce up to 2,000 eggs per day over a 20-year lifetime. When living and feeding conditions begin to pressure the colony, winged mature reproductives (alates) develop and swarm to find new sites. Subterranean termites use the tiniest of sheltered cracks or crevices to gain access to buildings, or they build earthen tubes up to several feet long to connect ground shelter with structural shelter—the tubes protect them from enemies and from desiccation. Drywood termites don’t need much moisture and simply carve out a small gallery, drilling distinctive “kickholes” to get rid of their fecal pellets.
Carpenter ants do not actually eat wood, but they carve out nesting cavities and tunnels in it. Since the wood is not a food source but just a material to be excavated, carpenter ants prefer moist, decayed wood (or insulation—rigid foam or cellulose). They rarely attack dry, sound wood. Carpenter ants feed on just about anything: dead insects, “honeydew” (the droppings of insects such as aphids, mealybugs, and whiteflies), and food scraps that we humans leave around our buildings. Often the main nest of the carpenter ant colony is outdoors in a nearby tree with an overhanging branch, foundation crack, or electrical line providing access to the building.
Carpenter ant colonies can grow to several thousand ants over a 3- to 6-year period, when, as with termites, alates develop and swarm to establish new colonies. Carpenter ant galleries, unlike termite galleries, are debris-free and have a sandpaper-like appearance. Carpenter ants are also more noticeable than termites, since they forage in the open for food and expel whatever wood they excavate (frass).
There are many types of powderpost beetle, but only a few species have the ability to
re-infest wood—that is, can complete their life cycles without bark or the living cambium beneath the bark. This is why observing the telltale exit holes of powderpost beetles is not a good indication of active infestation—the beetles may be long dead and gone. The most common type of re-infesting beetle is the true powderpost beetle: it attacks the softer sap and porous wood of susceptible hardwoods such as oak, hickory, ash, walnut, and cherry. Deathwatch beetles (so called for the late-night ticking sounds they sometimes make) and furniture beetles go after both hardwoods and softwoods, depending on the species of beetle.
Pest control strategies fall into several overlapping categories: chemical barriers, physical barriers, pest-resistant building materials, and
in situ elimination of pests. An examination of these demonstrates the evolution in pest control that has occurred during the past 50 years. Broad strategies are introduced here, and those strategies recommended for green buildings are summarized in an action-oriented Checklist below. An important element of effective pest control is the implementation of many common-sense construction practices that are only incidentally related to pest control. The most important of these are covered in the Checklist. Chemical barriers, physical barriers, and pest-resistant building materials are control strategies most related to termite management, with common-sense construction practices and
in situ treatments applying to all insect pests.
This is one of our oldest strategies for keeping insect pests, primarily termites, out of our buildings. The basic idea is to poison the earth around a building so that any termite heading to the building will be poisoned. The key is an insecticide that is highly lethal and long-lasting. For several decades, beginning in the mid-1940s, the chemical barrier of choice was chlordane, a chlorinated hydrocarbon related to DDT. A ground application would last many years—even decades—before losing effectiveness, and insect toxicity was very high. The problem was that chlordane was found to be carcinogenic and of a class of resilient chemicals that will bioaccumulate, threatening species near the top of the food chain. Under pressure from EPA to conduct a study of human indoor exposure to the product, chlordane was voluntarily withdrawn from the market in 1988. Manufacturers of heptachlor followed suit soon afterwards. (It is not uncommon for chemicals with an identified toxicity to be withdrawn from the market before they are banned, to limit the producer’s legal exposure).
One of the termiticides most widely used as a replacement for chlordane, chlorpyrifos (Dursban), has neither the same effectiveness as chlordane nor the in-field service life. But it too was found to have unacceptable human health effects, and for most uses the chemical is being phased out this year through an agreement reached between EPA and Dursban manufacturer Dow AgroSciences (see
The chemical barrier approach to insect pest control is largely a dead end. The need for high toxicity and long-lasting effectiveness is increasingly incompatible with our interest in health and environmental protection. While still used, chemical barrier pest control strategies are rapidly being replaced with the more integrated and safer approaches addressed below. Barrier insecticides have no place in green building.
What first comes to mind in this category for many residential builders are
termite shields—those strips of sheet metal flashing commonly installed on top of masonry foundations to keep termites out. Termite shields, it turns out, don’t really prevent termite entry; they force termites to build earth tubes around the shields. Because the tubes are visible, they provide an easy way to find termite infestations (as long as the foundation is regularly inspected). In order for the termite shield to be completely effective, it must be continuous along the foundation-frame interface and at all penetrations.
Two other physical barriers really do block termite entry, however: termite-barrier sand and a stainless steel screening called Termi-Mesh™. Sand barriers consist of either a 4”-thick (100 mm) layer of precisely sized sand or crushed stone beneath slab foundations, or two bands of the sand placed just inside the footer and along the outside of the stem wall of crawlspace foundations (see
Vol. 3, No. 2). The sand particles have to be too big for termites to move and small enough so that termites can’t squeeze between the inter-grain spaces. Grain size between 1.7 and 2.4 mm has been found to be most effective. Dr. Minoru Tamashiro of the University of Hawaii (now retired) discovered sand barriers—referred to as basaltic termite barriers or BTBs in Hawaii—during experiments with termites in different types of soil. He noted that the termites’ rate of progress in building tubes varied markedly with soil type.
Termi-Mesh was developed in 1988 in Australia, which has even more severe termite problems than Hawaii (the most severe in the U.S.). Termi-Mesh is a very fine, marine-grade stainless steel mesh that is impenetrable by termites and highly resistant to corrosion. Strips of Termi-Mesh are installed by Termi-Mesh professionals around the building’s foundation perimeter and wherever gaps and cracks may allow termite entry (see Termi-Mesh Stainless Steel Screening for Protection Against Termites).
Physical barriers require some changes in the way we build. In the case of termite-barrier sand, a new component is introduced as part of the foundation and slab installation that has to be carefully installed, tamped, and respected by subcontractors following its installation. Termi-Mesh installation requires careful coordination with the site superintendent and certain subcontractors, generally involving at least three site visits during construction. Also, at present, neither product is widely available outside of Hawaii.
Pest-resistant building materials
Another, very different approach to pest control is to assume that termites (and other problem insects) will be there and thus make our buildings unpalatable to these pests. We can build using materials that are either inedible or actually toxic to insects. Steel framing and masonry construction are popular in areas with significant termite problems for this reason. In some areas, such as Hawaii and the Virgin Islands, framing lumber and plywood pressure-treated with CCA or ACZA (ammoniacal copper zinc arsenate) are commonly used for 100% of house framing—both exterior and interior. Termites, carpenter ants, and powderpost beetles won’t eat or tunnel through most treated wood—though they can usually cross over it safely in search of untreated wood. Downsides to framing houses entirely out of CCA- or ACZA-treated wood include the risk to workers during installation, environmental problems associated with the life cycle of these compounds (see
Vol. 6, No. 3), and the fact that some homeowners dislike the idea of living surrounded by toxic heavy metals.
Fortunately, there is now an alternative in some parts of the U.S.: building houses out of borate-treated lumber and panel products. Louisiana-Pacific, Osmose, and U.S. Borax have teamed up to provide the SmartGuard family of products that can be used to create a Total Treated House (see SmartGuard Borate-Treated Wood Products Introduced for complete product review). Osmose wood treaters produce the Advance Guard™ line of lumber and plywood pressure-treated with sodium borate, while L-P incorporates zinc borate into SmartGuard OSB sheathing and subflooring and Cocoon PC (pest control) cellulose insulation. Unlike conventional pressure-treating chemicals, borates are considered harmless to humans. When protected from the weather, the solubility and resulting leachability of borates is not a problem.
The significant added cost of using preservative-treated framing and sheathing materials generally limits this approach to areas where the termite pressure or public concern warrants or even dictates this remedy.
In situ elimination of pests
The final pest control strategy covered here is to find and eliminate pests. Colonies of termites and carpenter ants can be located in buildings in a variety of ways—from termite-sniffing beagles to thermography (which shows off the heat generated by an infestation) to listening for the insects with a stethoscope. By precisely pinpointing the location of a colony, insecticide treatment can be limited to the specific area where it is needed, thus reducing chemical exposure elsewhere in the building.
Included in the arsenal of conventional treatment chemicals are organophosphates, synthetic pyrethroids, and the newest: a chloronicotinyl. In addition to these chemicals, there are some more environmentally friendly treatments. Borax (Na2B4O7·10H2O) and boric acid (H3BO3) have been used for remedial pest control for several decades, including such products as Tim-Bor
(R) from U.S. Borax and Bora-Care™ from Nisus Corp. (see
A very different treatment product is a biological termiticide called Bio-Blast, marketed by Paragon Professional Products since 1997. This is a naturally derived fungus,
Metarhizium anisopliae, which is lethal to termites. It can be mixed with water and sprayed into areas of infestation—killing termites within a few days to a few weeks. According to several termitologists with whom
EBN spoke, the limited field research suggests that Bio-Blast should not be used as a stand-alone soil treatment system, at least not without intense monitoring.
Another, more sophisticated and easier approach for eliminating existing colonies is to use a
bait system with a slow-acting, highly targeted pesticide. Dow AgroSciences (the company that recently agreed to phase out Dursban) introduced the Sentricon® System in the mid-1990s. With this system, special perforated tubes (Sentricon stations) are placed in the ground around the building (typically several dozen), each with a piece of wood (the food source) in it. These stations are inspected regularly for termite activity and, when feeding activity is found, the pieces of wood are replaced with a Baitube® device containing Recruit II® (hexaflumuron) termite bait. Termites found in the monitoring tubes are collected and physically put into the Baitube. The worker termites tunnel out of the Baitube and carry this bait back to the colony, leaving a scent that other termites can trace back to the food source. Recruit II is a slow-acting chitin synthesis inhibitor that interferes with the molting process in termites. The effect occurs long after the bait is eaten, providing separation between cause and effect, and preventing termites from making any association between the bait and its effects. The entire colony is usually destroyed.
Following elimination of the colony—which may take several months—the Recruit II bait is replaced with pieces of wood, and monitoring resumes. Though very effective, the Sentricon System is certainly not cheap. Rather than paying for a conventional pesticide application, the building owner buys a Sentricon service contract, which includes regular inspection as well as treatment with the bait as needed. Jim Selnow, co-owner of ProTech Termite and Pest Control of Springfield, Virginia, reports initial treatment costs at approximately $7 to $8 per lineal foot ($23 to $26 per meter) and $9 to $10 per lineal foot ($29.50 to $33 per meter) for large commercial and residential projects, respectively, with annual follow-up running between 13% and 15% of pretreat costs.
In addition to Sentricon, there are several competing systems on the market, including FirstLine from FMC Corp. and Exterra® from Ensystex, Inc. A do-it-yourself termite bait system—Terminate™ from United Industries Corp.—has also been introduced, but complaints have been filed against the company by the Federal Trade Commission and several state attorneys general claiming deceptive and unsubstantiated advertising claims.
Interestingly, the shift to an advanced bait system has been driven not only by its effectiveness, but also by today’s job market. People entering the pest control business today have been brought up to be much more circumspect about chemicals and are much less willing to spend all day applying them. The bait systems are easy and very safe for pest control professionals to use.
There are several less widely known, non-chemical spot treatments, including microwave heat treatment; a high-voltage, low-amperage electric gun; and liquid nitrogen injection. The Bio-Integral Resource Center (see information resources below) has detailed information on these techniques.
There are two methods of treating an entire structure for insect infestations: chemical fumigants and heat treatments. Both are commonly used for one-time control or eradication of many insects, including ants, powderpost beetles, and drywood termites. These treatments are generally performed by a small subset of pest management firms because of the special licensing required for fumigants and the special equipment required for both. The chemical fumigants used—methyl bromide and sulfuryl fluoride—are highly toxic and involve a multi-day evacuation of the building. Heat treatments involve wrapping the structure to keep heat in and wrapping building contents such as electronics for thermal protection. Core wood temperatures must reach 120°F (49°C) for at least 30 minutes, generally involving bringing the whole structure to about 160°F (71°C) for more than an hour (about the temperature of a sauna). Problem areas involve wood in contact with large heat sinks, such as sill plates on foundations—this may be why the technique is not commonly used for subterranean termite infestations. Both whole-structure heat treatment and fumigation techniques are more common in the South and on the West Coast, where wood-boring insect pressures are the greatest.
The Checklist above summarizes the most appropriate (and greenest) strategies for control of wood-destroying insects.
There has been a veritable revolution in the control of termites and other building-structure insect pests. The old days of creating a toxic barrier around buildings are almost gone. In place of chemical barrier treatments, we have a wide range of building practices, physical barriers, and highly targeted baits that can eliminate insect pests with very minor risk to human health or the environment. Insect pest problems are indeed getting worse, but our ability to safely and effectively manage them is getting much better. We may save New Orleans after all.