Structural and Public Health Pests: Termites

Pest Management In and Around Structures October 15, 2009 Print Friendly and PDF

Termite prevention and control is inextricably linked to building construction type and quality. In schools, structurally damaging termites generally belong to one of two groups: drywood termites (family Kalotermitidae) and subterranean termites (family Rhinotermitidae). Most school buildings, with the exception of wooden portables, are constructed with concrete and steel. Therefore, termites do not generally pose a great risk to the structure. However, the contents, including cabinetry, can be subject to damage by termites belonging to both groups. It is important to identify the termite you are dealing with because control measures can differ significantly for each species.

Table 8.61 Termite species.

Common and species name Geographic distribution
drywood termite Southern US from Florida to California.
Formosan subterranean termite, Coptotermes formosanus Southeastern US and Southwestern California.
southeastern drywood termite, Incisitermes snyderi Southeastern US.
western drywood termite, Incisitermes minor Central Arizona west to California and north to Washington State.
West Indian drywood termite, Cryptotermes brevis Hawaii, Florida and west to Louisiana.
subterranean termites Throughout the US except Alaska, with highest populations in the Gulf and Southeastern states.

All termites are true social insects, living in colonies. Drywood termite colonies contain reproductives, soldiers (which defend the colony), nymphs and immature forms called pseudergates or ―false workers (which perform most of the work in the colony). Drywood termites most commonly infest dry, sound (non-decayed) wood and are a problem more commonly associated with older schools.

Subterranean termites are the most significant pest termite group in the US. There are over 45 species of termite in the US. Subterranean termites belonging to the genera Reticulitermes, Heterotermes and Coptotermes are among the most damaging. Colonies can range from a few thousand up to 10 million individuals. They predominantly live in the soil, although it has been estimated that 20% of some species can nest aerially, without ground contact, under the right conditions. Whereas a drywood infestation starts with only two individuals in a wooden member, a house could literally be built over a huge colony of subterranean termites. Once the land is cleared for building, the only food source left in place is the new structure, which is why thorough termite pretreatments are important. There are several effective chemical and non-chemical control options, of which the most important is proper building construction.

Subterranean termites cause over $2 billion in damage, treatment, and repair of damage to structures annually in the US. Subterranean termites not only damage structures, but also their contents, including paper, family photographs, documents, cardboard and the like. They gain access most commonly through the outside foundation wall, especially those that have been covered with exterior insulation and finishing system installed below grade, or through plumbing and utility conduits. Bathrooms and kitchens are common entry points. Damage to structures and personal effects caused by this type of termite is the most common cause of litigation between service providers and clients.

Table 8.62 Drywood and subterranean termite comparison.

Termite Usual Location Damage Frass Control Methods
drywood dry, sound wood along and across wood grain six-sided pellets, dry wood replacement, spot treatment, fumigation
subterranean (control options for arboreal species are included here) soil along wood grain sticky, incorporated into mud tubes and galleries structural modification, liquid or granular chemicals, baits, physical barriers


Monitoring and inspection for drywood termites

A telltale sign of drywood infestation is the accumulation of six-sided fecal pellets. Fecal pellets are also known as ―frass. Termites inside infested wood push frass out through pencil-tip sized ―kick-out holes (1-2 mm diameter) in infested material. Frass can resemble ―sawdust or ―coffee grounds , but are distinctly six-sided. The pellets have a gritty texture when rolled between your fingers and can be from light brown to almost black in color. The color is not related to the age or the color of the wood. Pellets usually collect into piles on the floor and other surfaces. Drywood termites can infest wood flooring, framing members, window sills, doors, fascia boards and furniture. They are also known to infest attics where the temperature of the wooden members can exceed 110 F. A sign of advanced infestation is surface blistering or warping. Drywood termites sometimes tunnel just under the surface of the wood giving it a blistered, uneven appearance. Infestations may be detected by tapping the wood every few inches with the handle of a screwdriver or by probing with a sharp tool. Damaged wood sounds hollow - a papery, rustling sound indicates tunnels just beneath the surface.

Three of the most common drywood termites in the US include:

  • The West Indian drywood termite soldier is easy to identify by its distinctive ―phragmotic head, which resembles a burnt match and is used to block the tunnels in the termite gallery system to protect the colony from intruders, especially ants. This termite typically infests picture frames, furniture, boxes and structural woodwork. Interestingly, this species is never found in natural environments but only in wood in human-made structures. Depending on location, this termite usually swarms from April to early July and November to early December.
  • Southeastern drywood termite colonies are generally larger than those of the West Indian drywood termite and occupy larger pieces of wood. These termites are found in both natural and human-made environments and are the most common drywood in Florida. Development of the colony is slow, but structural damage can be extensive if multiple colonies are present in the same structure. This termite usually swarms from May through November in most locations.
  • The Western drywood termite (Incisitermes minor, is a non-native termite and is the number one drywood termite pest in the western US. Depending on location, it usually swarms from the end of August through November.

Cultural and physical options for drywood termite management

Used lumber, furniture and other wooden articles should be carefully inspected for termite infestations. Drywood termite reproductives may enter a building through the attic or foundation vents, under or directly through shingles or under eaves. All vents, doors and windows, especially those in the attic, should be screened with 20-mesh screen. A good coat of paint on exposed wood will provide some protection against termite entry. Before painting, all cracks and crevices should be filled with putty or plastic wood. Pressure treated wood is resistant to termite attack. Certain woods are also naturally resistant to termites including heart wood of redwood, bald-cypress, mahogany and Spanish cedar. These woods can be more expensive and will become susceptible after several years of aging and weathering.

Construction should be designed to eliminate moisture and water leaks. Remove and replace infested or damaged wood. Microwaves, electroguns and liquid nitrogen require thorough access to wood. Heat treatment can be used for whole structure or compartment treatments.

Carefully inspect wooden objects including furnishings and equipment before moving from one school building to another to avoid introducing drywood termites.

If damage is localized, a drywood termite colony may be controlled by removing and replacing the damaged wood. It is very important to carefully inspect all woodwork in the building for pellets and/or damaged wood, especially in attics, baseboards, windowsills, floor joists and furniture.

Pesticide options for drywood termite management

Take time to research pest control companies and treatment options for your construction type. Soil treatments, either with liquid insecticides or termite baits are ineffective because drywood and dampwood termite colonies are inside the wood, not in the ground.

Localized treatments of infested wood for drywood termites include injecting insecticide directly into a termite gallery through kick-out holes or holes made with a drill. Applications can also be made to cracks and crevices such as the spaces between wooden pieces or between different building materials, such as wood and concrete,directly treating infested wood. Products registered for wood treatment are usually liquids applied by spraying it onto the wood.

If the infestation is too extensive and advanced for local treatment, it may be necessary to tent and fumigate the entire building. Although this method can be very expensive and disruptive, it may be the only option that will kill all termites in the structure.

Sulfuryl fluoride gas is used to create a toxic atmosphere within a confined space; under a tarp, within a sealed structure or inside a fumigation vault. After fumigation, the structure is cleared of sulfuryl fluoride and thus termites are not prevented from re-entering the structure. Because sulfuryl fluoride is odorless and colorless, chloropicrin (―tear gas) is used as a warning agent.

Inspection and monitoring for subterranean termites

Mud tubes, wood damage and termite wings (attached or detached) are common telltale signs of an infestation. Subterranean termites build earthen, shelter tubes to protect them from low humidity and predation. These tubes are usually ¼" to 1" wide. Structures should be inspected at least once a year for evidence of tubes, particularly around the outside foundation walls and plumbing penetrations and pipe conduits. Cracks in concrete foundations and open voids in concrete block foundations are also hidden avenues of entry. Wood damaged by subterranean termites is often not noticed because the exterior surface usually must be removed to see the damage. However, galleries can be detected by tapping the wood every few inches with the handle of a screwdriver. Damaged wood sounds hollow, and the screwdriver may even break through into the galleries.

General inspections for subterranean termites can be difficult because of the cryptic lifestyle of these insects. Laws and regulations will vary from state to state on inspection requirements.

Cultural and physical options for termite management

The best option for avoiding subterranean termite damage is prevention initiated during planning and construction. Prevention should include:

  • Removal of all stumps, roots, wood, and similar materials from the building site before construction is begun.
  • Removal of all form boards and grade stakes used in construction.
  • There should be no contact between the building woodwork and the soil or fill. Exterior woodwork should be located a minimum of 6 inches above ground and beams in crawl spaces at least 18 inches above ground to provide ample space to make future inspections.
  • Ventilation openings in foundations should be designed to prevent dead air pockets and of sufficient size to assure frequent changes of air -- at least 2 sq. 25 running feet of outside foundation wall. This helps keep the ground dry and unfavorable for termites.
  • Landscape plants and irrigation should not be placed within two feet of the foundation wall.
  • Thorough annual inspections should be conducted to discover evidence of wood damage or termite activity such as shelter tubes on foundation surfaces, discarded wings or adult termites.
  • Any wood that contacts the soil, such as fence posts, poles and general foundation structures, should be commercially pressure treated, and should not be attached to house.

Once termites find a structure by tunneling, tubing or surface foraging, they need moisture to establish and continue the infestation. Moisture related factors account for as much as 95% of those contributing to termite infestation. Examples of conducive conditions relating to moisture include:

Leaky roofs, water heaters and pipes.

  • Improper grading resulting in soil contact with structure above foundation.
  • Improperly flashed windows, roofs, chimneys.
  • Exterior Insulation and Finish Systems (EIFS) installed below grade wicks moisture into walls and obscures inspection space.
  • Improperly installed wall systems, such as using plastic vapor barriers. *Installing rigid foam board insulation below grade (wicks moisture).
  • Absent or inadequate number of ―weep holes or holes obstructed by debris.
  • Mulch pushed up against the house, obscuring inspection space.
  • Irrigation directed toward the house.
  • Landscape planted within 2 feet of the house.
  • No gutters.
  • Gutter downspouts directed toward wall of house or not far enough away.
  • Air-conditioning condensate lines too close to house.
  • Improperly installed windows.
  • Inadequate vapor barrier coverage under slab.
  • Inadequate ventilation of crawl spaces and attics.

Physical barriers include stainless steel mesh installed at entry points including wall cavities, piers and plumbing penetrations. Particle-size barriers have been available for many years, but have not gained wide acceptance by the building construction industry.

Table 8.63 Commonly used products for physical or cultural management of termites and uses.

Type Example Products Uses
barriers Termi-Mesh™ Termite Barrier Install during construction.
heat Same as above Same as above
cold, liquid nitrogen Same as above Same as above

Pesticide options for termite management

Preconstruction soil termiticide treatments are categorized as ‖repellent‖ or ―non-repellent.‖ Repellent termiticides include the pyrethroid class of insecticides. While these termiticides have good performance histories in USDA Forest Service trials, construction and landscaping practices that cause breaks and gaps in the chemical barrier compromise efficacy. Termites detect repellent chemistries at concentrations as low as 1 ppm. Termites will avoid the area and the structure will be protected only if the barrier remains continuous. Breaks in the barrier unavoidably occur during the construction process, creating untreated gaps through which termites can enter structures.

Non-repellent termiticides work to protect structures because termites unsuspectingly forage into treated areas, acquiring a lethal dose of the termiticide. The toxicant may act slowly enough that exposed individuals transfer the toxicant to other individuals in the colony through grooming and trophallaxis. The result of this transfer is death for many termites that are secondarily affected. The non-repellents have generally held up well in the USDA Forest Service trials.

Finally, wood treatments, specifically Boracare (Nisus) and baits (Sentricon, DowAgro Sciences) have been accepted by several states as stand-alone treatments for new construction.

Table 8.64 Commonly used pesticide products for termites and uses. a. Insecticides carrying

a CAUTION label or exempt from EPA registration, in formulations that reduce potential for exposure.

Active ingredient Example Products Uses
diflubenzuron Prescription Treatment® Advance® Compressed Termite Bait 499-488 Bait block used in bait station.
hexaflumuron Sentricon® AG III 62710-454 Bait block used in station for subterranean termites.
lamda-cyhalothrin Impasse™ Termite System 100-1125

Impasse™ Termite Blocker 100-1166

Polymer laminate barriers impregnated with insecticide and installed prior to slab construction.

b. CAUTION-label formulations with greater potential for exposure.

Active ingredient Example Products Uses
imidacloprid Premise® Foam 432-1391 Foam applied as a spot treatment for drywood termites.
imidacloprid Premise® 75 432-1331 Dampwood and drywood termites.

c. Formulations with greater potential for toxicity and/or exposure.

Active ingredient Example Products Uses
boric acid Bora-Care™ 64405-1 Tim-Bor 64405-8 Drywood termites.
chlorfenapyr Phantom® 241-392 Drywood, southeastern termites.
cypermethrin Demon® TC 100-1006 Dampwood, drywood termites.
deltamethrin DeltaDust® 432-772 Dampwood, drywood termites.
fipronil Termidor® SC 7969-210 Drywood termites.
sulfluryl fluoride Vikane® 62719-4 Zythor® 81824-1 Fumigant for drywood termites.
thiamethoxam Optiguard ZT 100-1170 Drywood termites.

Table 8.65 Priorities for termite management.

Research Efficacy of boric acid pretreatments.

Additional resources for termite management

Koehler, P.G., and C.L. Tucker. 2003. Subterranean Termites. University of Florida.

Scheffrahn, R.H., and N. Su. 1997. Drywood Termite Control: Weighing All the Options. University of Florida. (PDF)

University of California. Termites. In How to Management Pests of Homes, Structures, People and Pets.

University of Florida. 2006. Termites in Mulch. Pest Press. (PDF)

University of Florida. Termites and Other Wood-destroying Insects.

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This work is supported by the USDA National Institute of Food and Agriculture, New Technologies for Ag Extension project.