| |
Q. HOW CAN I DETECT DRYWOOD TERMITES?
A. Drywood termites are secretive insects and are difficult
to detect. They live deep inside wood and, except during periods
when they swarm or when repair work is being done on infested
homes, they are seldom seen. Colonies are small (usually fewer
than 1,000 individuals), can be widely dispersed, and take years
to mature. While a homeowner may initially detect the presence
of termites when they swarm or if fecal pellets are discovered,
inspecting for drywood termites and determining the extent of
an infestation require experience.
The minimum requirement by California state law for drywood
termite inspections includes visual searches of accessible areas.
However, detection of difficult-to-find infestations may require
removal of walls, paneling, and stucco as well as the use of
ladders and scaffolds.
Q. HOW DO INSPECTORS DETECT DRYWOOD TERMITES?
A. During a visual inspection for drywood termites, inspectors
look for feeding damage, shed wings, termite fecal pellets,
and kickout holes, which are small holes the size of BB shot
through which termites push fecal pellets out of the wood. Fecal
pellets, hexagonal in shape, are diagnostic for drywood termites.
However, whether the infestation is currently active or what
the extent of the infestation is cannot be determined from pellets
alone. Cleaning up the fecal pellets around a kickout hole and
checking a few days later to see if new pellets have appeared
can help to determine if an infestation is active. (Building
vibrations/movements may cause some pellets to appear.) If an
active infestation of drywood termites is found in your structure,
you should have it treated.
Other detection methods include the use of dogs, odor detectors,
and feeding-sensitive (acoustic emission) devices, but these
are infrequently used. Fiber optics, borescopes, and movement-sensitive
devices using microwaves have also been tried, but their reliability
has not yet been scientifically tested on drywood termites.
Except for feeding-sensitive devices, most detection methods
are still considered experimental because adequate research
has not been conducted on their effectiveness. Visual searches
by inspectors for evidence of termites and damage remain the
mainstay of the industry.
Q. HOW ARE EXISTING INFESTATIONS ELIMINATED?
A. All drywood termite control methods can be categorized
as either whole-structure or localized. A whole-structure
treatment is defined as the simultaneous treatment of all infestations,
accessible and inaccessible, in a structure. A localized or
spot treatment is more restrictive, often applied to a single
board or small group of boards. Homeowners are advised to know
the distinction between whole-structure and spot treatments
when deciding which method to select because all treatment methods
are not equivalent.
Whole-structure treatments have an advantage over spot treatments
in that they can eliminate all infestations, even hidden ones.
With the uncertainty of current detection methods, particularly
when drywall or other wall coverings conceal infestations, there
is always some doubt as to the extent of dry-wood termite colony
boundaries within homes. Consequently one can never be sure
that all infestations have been treated when applying spot treatments.
Q. WHAT OPTIONS ARE AVAILABLE FOR WHOLE-STRUCTURE TREATMENTS?
A. Fumigants (sulfuryl fluoride) treat all infestations
simultaneously and have high levels of efficacy if correctly
applied. Sulfuryl fluoride kills drywood termites in about 3
days. A monitored fumigation, which involves installing gas
monitoring lines inside the structure undergoing treatment,
has the highest rate of treatment success. Nonmonitored fumigation
may not have enough gas concentration to kill infestations,
and failures may occur. Fumigation's advantage over localized
treatment is that it may eliminate infestations that are hidden
from view. Major issues to consider with the use of fumigants
include the difficulty of installing tarpaulins, the difficulty
in determining the proper dosage, the need to protectively bag
food items, and the lack of residual control. Residual control
means long-term protection (several years or more) from drywood
termite attack. (Generally, only chemicals added to or onto
wood provide residual control.) It will also be necessary to
vacate the structure for 2 to 3 days while it is being treated
and then ventilated. Additionally, roofs may be damaged by having
tarpaulins dragged across them.
Methyl bromide was another fumigant used for many decades in
California to control drywood termites. However, because of
environmental concerns about the atmospheric ozone layer, the
strong odors of some formulations, the long aeration times for
fumigated structures, and the need for extensive aeration buffer
areas around structures, this fumigant has been phased out for
urban use in California.
Q. WHAT NONCHEMICAL OPTIONS ARE AVAILABLE FOR WHOLE-STRUCTURE
TREAMENTS?
A. Heat is a nonchemical option for whole-structure treatments.
Excessive heat kills drywood termites by disrupting cellular
membranes and denaturing enzymes needed for their survival.
The treatment process involves heating all wood in the structure
to a minimum of 120¡F and holding this temperature for at least
33 minutes. The benefit of heat treatment is the ability to
treat the entire structure without the use of chemicals and
the relatively short period of time the structure must be vacated
(hours instead of days, as with the use of fumigants). An additional
advantage is that portions of large structures can be treated
separately, which is very useful in apartments and condominiums.
The major drawbacks of heat treatments include the difficulty
in raising the internal core temperature of large structural
beams that are infested and heat sinks, which are areas within
the structure that are difficult to heat, such as wood on concrete
or tile. As more powerful and efficient heaters are developed,
larger homes can be efficiently treated with heat.
Other issues to consider include damage to heat-sensitive items
in homes including plastics (e.g. electrical outlet covers)
and cable wiring. Also, like fumigants, heat treatments have
no residual control. Of course, preventive chemicals can be
applied to areas treated with fumigants or heat for long-term
protection.
Q. WHAT LOCALIZED OR SPOT TREATMENTS ARE AVAILABLE?
A. There are many localized/spot treatment methods available
that include both chemical and
nonchemical options. The chemical options include aerosol pyrethrum
and aerosol and liquid pyrethroids (cyfluthrin, permethrin,
bifenthrin), liquid imidacloprid, liquid nitrogen, and liquid
and dust formulations of disodium octaborate tetrahydrate. Chemicals
that have been phased out of commercial use include organophosphates,
carbamates, silica-gel, and dri-die. For liquid and dust insecticides
to be effective, termites must touch or ingest them. Spot treatments
should be applied only by licensed applicators. Home use products
are not effective.
Depending on the chemical used for spot treatments, laboratory
studies have shown a variation of 13% to 100% in their effectiveness
in controlling drywood termites. However, many of these chemicals
have not been tested in large-scale field-tests. A newer insecticide
(imidacloprid) with very good lab and field results is available
and will be used increasingly in California. Botanical-based
products (orange oil and neem oil) have been tried, but there
are no published studies that verify the efficacy of these materials
in controlling drywood termites. Recent experiments evaluating
surface or gallery injections of aqueous disodium octaborate
tetrahydrate did not effectively control a closely related species
of drywood termites, Incisitermes synderi (Scheffrahn et al.
1997).
Liquid nitrogen is different from other spot treatment methods
in that its mode of action is thermal; it causes a sudden drop
in temperature, which kills the termites. Laboratory studies
have shown drywood termites are killed after momentary exposures
of temperatures in the range of -5.8¡F to 1.4¡F when temperatures
were lowered from room temperature at a rate of 33.8¡F per minute
(Rust et al. 1997). Studies on liquid nitrogen show that dosages
exceeding 30 pounds per enclosed wall space between 2 by 4s
achieve high levels of effectiveness. Although most chemicals
used for spot treatments give long-term control, liquid nitrogen
has no residual activity when used alone. Minor damage to the
structure occurs from the holes drilled for spot treatments
of chemicals and for liquid nitrogen insertion. For all chemical
spot treatments, including liquid nitrogen, it is critical that
all infestations in a structure are detected so that they all
receive treatment.
Q. WHAT NONCHEMICAL OPTIONS ARE AVAILABLE FOR SPOT OR LOCALIZED
TREATMENTS?
A. There are four nonchemical options for drywood termite
control with spot or localized application.
- Heat,
which is used for both spot and whole-structure treatments,
is one option. The advantages and disadvantages discussed
for heat as a whole-structure treatment also apply to spot
treatments.
- Microwave
devices are also available for drywood termite control.
Microwaves kill termites by causing fluids inside their
cells to boil, which destroys cell membranes; in short,
the termites are cooked inside the wood. There are a number
of firms now offering microwave treatments. One advantage
of microwaves is their relative portability; another advantage
is that they leave no chemical residue. When using microwaves,
however, detection accuracy is critical to success. Both
microwaves and heat treatments may damage the surface or
interior of wood boards, depending on the power of the device.
(The wattage or power of microwave or heating devices may
vary from several hundred to more than 10,000 watts.) Lab
studies revealed no relationship between increasing microwave
wattage and drywood termite mortality (Lewis et al. 2000).
As with heat treatments, it may be difficult to heat areas
with heat sinks to high enough temperatures with microwaves
for effective control.
- High
voltage electricity, or electrocution, is another nonchemical
option for controlling drywood termites. The device currently
marketed uses high voltage (90,000 volts) but low current
(less than 0.5 amps). Death to drywood termites occurs by
electric shock, although delayed mortality may also occur
from the destruction of intestinal protozoa. The advantage
of electrocution is that the equipment is portable. The
limitations include detection accuracy and the possible
reduced efficacy from the interfering actions of common
building materials, for example metal, concrete, and glass.
If drill holes are used to enhance the flow of current into
wood, damage occurs to wall coverings, walls, and structural
wood members.
- Wood
replacement is another remedial treatment option. However,
similar to other spot treatments, its effectiveness is highly
dependent on detection accuracy and extent and location
of the infestation, and it may be expensive to accomplish.
There
is little research on biological control of drywood termites.
Biological control is the use of other life forms (e.g., insects,
nematodes, or microbes) to control pest insects. Although
predators, parasites, and pathogens have been shown to control
other insect pests, their efficacy for drywood termite control
has not been explored.
Q. ARE LONG-TERM PREVENTIVE TREATMENTS AVAILABLE?
A. Although chemicals are commercially available in California
for long-lasting prevention against infestation, there is
little data on their effectiveness against the drywood termites
that occur in California. Recent research from the University
of Florida demonstrates that new colony establishment by another
species of drywood termite, Cryptotermes brevis, could be
prevented using dust formulations of commercially available
disodium octaborate tetrahydrate (Scheffrahn et al. 2001).
Drawbacks with some chemical preventive treatments include
damage from drill holes and unsightly appearance from dusts.
Pressure-treated wood (chemically treated wood that is green
in color) for drywood termite prevention can be effective
for species that occur in California. However, the use of
most wood preservatives has been restricted. Painting of wood
with enamel, shellac, or varnish gives very little protection
against drywood termite feeding.
Q. WHAT NONCHEMICAL, LONG-TERM PREVENTIVE
METHODS ARE USED?
A. Integrating nonchemical and chemical treatments to
ensure that termites are not able to colonize over the long
term is a strategy used by some pest control professionals.
Nonchemical, long-term preventive methods include physical
barriers, such as metal screens. Resistant woods can reduce
but do not eliminate damage. There are few studies that demonstrate
the efficacy of combinations of methods or of nonchemical,
long-term preventive treatments directed against drywood termites.
Q. DID I MAKE THE RIGHT CHOICE?
A. When planning treatment for drywood termites, consider
whether the whole structure is to be treated or just localized
areas. Localized/spot treatment methods make it more difficult
to ensure complete control because of the difficulty in determining
the extent of a drywood termite infestation. There also appears
to be considerable variation in effectiveness of various techniques
from applicator to applicator. Read your guarantee carefully;
you may wish to consider an annual inspection service. Also
important is a company's reputation. There are thousands of
pest control companies in the state. They don't all have the
same services or performance. Obtain at least three vendor
bids before you decide. Check the reliability of the vendor
by asking for client referrals and check the status of its
business license and consumer complaints with the California
Department of Consumer Affairs, Structural Pest Control Board,
in Sacramento and with your local Better Business Bureau.
For added information on safety of chemicals to humans and
structures, request the Material Safety Data Sheets or equivalent
information for nonchemical control methods from the pest
control company.
In summary, research indicates that if you correctly locate
the colony and get the chemical or nonchemical treatment directly
onto the termites, the effectiveness of control will be high
(90%). For failed treatments, an additional callback treatment
may lead to better results.
>Back
to FAQs index page
|
|
