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Chapter 20
TERMITES
AS
PESTS
OF
BUILDINGS
Nan-Yao
Su
and RudolfH. Scheffrahn
Ft.
Lauderdale
Research
and
Education
Center,
University
of
Florida,
3205
College
Ave.
Ft.
Lauderdale,
FL
33314,
U.S.A.
Key words: Tennite control, tennite pests, Rhinotennitidae, Kalotennitidae, insecticide barriers, tennite baits,
fumigation, local and compartmental treatments.
Abstract:
Of
the more than 2,300 tennite species in the world,
183
species are known to damage buildings and
83
species cause significant damage. Subterranean tennites, including mound building and arboreal species,
account for 147 (80%)
of
the economically important species. The genus
Coptotermes
contains the largest
number
of
pest species (28), whereas the genus
Cryptotermes,
especially
Cr.
brevis,
is the most widely
introduced. The world-wide economic impact figure
of
tennites
is
uncertain, but the control cost for tennite
pests
in
the United States was estimated at $1.5 billion annually in
1994.
Because
of
differences in their life
histories, control measures differ between subterranean and drywood species. Insecticide barriers are used
for exclusion
of
soil-borne subterranean tennites, whereas slow-acting baits are used for population control
of
subterranean tennite colonies
in
and near structures. Whole-structure treatments (fumigation and heat),
compartmental treatments (heat or cold), and local treatments (wood surface treatments or insecticide
injection) are the primary tools for drywood tennite control.
1.
ECONOMIC
IMPACT,
PEST
SPECIES
AND
THEIR
DISTRIBUTION
Tennites are known to cause damage to
buildings throughout the tropics, sub-tropics
and temperate regions. But there are insufficient
data to accurately assess their economic impact
world-wide. Regional differences in cost
of
living, cultural practices, and human attitude
toward termites all contribute to the uncertainty.
For example,
an
organized service industry
providing termite control is scarce in much
of
the tropics where most
of
the destructive
termite species are found, yet the presence
of
a
single species such
as
the Formosan
subterranean termite, Coptotermes formosanus
Shiraki, in the United States can sustain a
437
multimillion-dollar termite control industry.
Based on sales figures for liquid termiticides,
the control cost alone in the United States might
exceed
$1.5
billion annually [111]. A brief
survey conducted
for
structures damaged by
Co.
formosanus in New Orleans indicated
typical homeowners may pay 5 times more than
the control cost to repair structural damage
(E.
Bordes, New Orleans Mosquito and Termite
Control Board, unpublished data).
Of
the over 2,300 termite species in the
world,
183
species are known to damage
buildings and
83
species cause significant
damage
[25].
Subterranean termites, including
mound building and arboreal species, account
for
80% (147)
of
the economically important
species. Most
of
the economically important
subterranean species are found
in
the tropics,
including
26
species in the Indian sub-
continent,
24
species in tropical Africa, and
17
T.
Abe
et al. (eds.), Termites: Evolution, Sociality, Symbioses, Ecology, 437-453.
© 2000 Kluwer Academic Publishers.
438
species in Central America and the West Indies.
Only 9 subterranean species are considered
pests
of
buildings in North America. In
Australia,
16
termite species are
of
economic
importance. The genus Coptotermes contains
the largest number
of
pest species (28),
followed by Odontotermes (16),
Microcerotermes (15), Reticulitermes (11), and
Heterotermes (10). Coptotermes
spp.
are also
the most wide-spread among the subterranean
termite pests. Coptotermes formosanus, for
example, has been introduced to at least 6
zoogeographic regions, whereas
Co.
haviland;
Holmgren is found in 5 regions worldwide [25].
Other wide-spread subterranean species
are
R
jlavipes (Kollar)
(3
regions), and
R.
lucifugus
(Rossi)
(4
regions).
Drywood termites constitute a diverse and
primitive family
of
about
500
wood-dwelling
and one soil-inhabiting species
[61].
Less than
10%
are primary or occasional pests
of
sound,
dry
structural lumber and wooden furniture and
occur in all tropical, subtropical, and some
temperate regions. Cryptotermes, Incisitermes,
and Kalotermes contain the bulk
of
pest species
worldwide
[25,
49].
Species requiring more
wood moisture than is provided by ambient
relative humidity alone are often referred
to
as
a
dampwood termites (e.g. most Neotermes and
Gyptotermes spp., many Kalotermes spp., some
Incisitermes and Cryptotermes, and all
Termopsidae), but the distinction between
"drywood" and "dampwood" is often unclear.
Dampwood species can be pests
of
structural
lumber exposed to water from rain
or
soil.
Drywood termites account for a
considerable portion
of
the damage and control
costs attributed
to
termites in the United States
[115]
and worldwide losses are not fully
documented, but likely exceed that
of
the
United States. In
1987,
the cost
of
fumigations
for
drywood termite control in southern Florida
was conservatively estimated
at
$30
million
[97].
In the city
of
Corpus Christi, Texas,
drywood termites accounted for over
$2
million
ofthe
$3.7 million in total termite losses during
1979
[45].
CHAPTER 20
Drywood termite colonies nest and forage
solely in wood and give
few
outward signs
of
their presence except during brief dispersal
flights. Therefore, they are easily and
unwittingly transported
by
the movement
of
infested goods, containers, or ships
[36,
79].
Once introduced into suitable warmer climates,
drywood species often thrive. New arrivals may
even flourish in heated structures in cold
temperate regions
[42].
Although not native
to
the West Indies, Cryptotermes brevis (Walker)
has been introduced to every inhabited island
there
[99],
and
is
the most widely introduced
and most important drywood termite pest
world-wide
[36].
Its origin, however, remains
obscure [104]. Other Cryptotermes that have
become pests beyond their original range
include the Indomalayan
Cr.
cynocephalus
Light,
Cr.
domesticus (Haviland), and
Cr.
dudleyi Banks, and the African
Cr.
havilandi
(Sjostedt)
[36,
37,
104].
Incisitermes minor
(Hagen), native
to
the southwestern United
States, is now established in Florida [97], Japan
[141], and Hawaii (R. SchefIrahn, unpublished
observations). Incisitermes snyderi (Light)
occurs in the southeastern U.S. while the more
xeric-adapted Marginitermes hubbardi (Banks)
is a structural pest in the southwestern U.S.
deserts
..
Kalotermes flavicollis
F.
is a pest
of
the Mediterranean region
[25].
Because
infestations by kalotermitids
are
usually
diagnosed by fecal pellets, damage,
or
discarded wings, it is probable that many more
species infest structures than are currently
known. For example, Tauritermes vitulus
Araujo and Fontes was described from
collections in
dry
structural lumber in southern
Brazil
[8].
2.
CONTROL MEASURES
Subterranean species live mostly in soil and
become pests when foraging activity extends
into man-made structures (Figure
1).
Damage is
initiated mostly by foraging castes,
i.e.
pseudergates or workers. Mound-building or
20.
TERMITES
AS
PESTS
OF
BUILDINGS
Figure
1.
Subterranean termites live mostly in soil and
become pests when foraging activity extends into man-
made structures. The objective
of
barrier treatments is
to
exclude soil-borne subterranean termites from structures,
while baits are used
to
control the colony populations. One
such population control approach
is
the monitoring/baiting
program. First, stations containing monitoring devices are
installed
in
soil surrounding a structure. When termites are
detected in the stations, the monitoring devices
are
replaced with tubes containing hexaflumuron baits.
Following bait applications and when termite activity has
ceased in the stations, bait tubes
are
replaced with
monitoring devices for continuing the monitoring
program.
arboreal tennites build nests above-ground, but
akin to subterranean tennites, they also enter
buildings from the ground. On some occasions
when conditions are suitable (consistent
moisture problem, protected microhabitat, etc.),
alates
of
subterranean tennites may initiate
aerial infestations. Being restricted to foraging
in wood, drywood tennites colonize structures
solely during dispersal flights. Because
of
the
differences in their life history, control
measures differ between subterranean and
drywood species.
2.1 Control
of
subterranean
termites
Current control options include placement
of
chemical and physical barriers, wood
treatments, and population control using baits
(Table
1).
439
2.1.1 Insecticidal barriers
The objective
of
barrier treatments is to
exclude soil borne subterranean tennites from
structures (Figure
1).
The barrier systems are
placed before the installation
of
a building
foundation. In the United States, liquid
insecticide is applied onto sub-slab soil at a rate
of
4.1
liter/m2 (and 5 liter/m along the
foundation perimeters) [80], but application
rates may vary in different regions. For existing
buildings, insecticides are applied in trenches
excavated along the foundation walls, and/or
beneath building foundations by rodding to
create
an
insecticide barrier around the
building. Additionally, slab flooring, especially
along the foundation wall and near the utility
pipes, may be drilled to inject insecticide.
Soil treatments with liquid insecticide have
been widely used by commercial tennite control
firms for subterranean tennites since the early
1900s [89]. Insecticides used for ground
treatments in the United States during the 1930-
1950's included sodium arsenite,
trichlorobenzene, DDT, pentachlorophenol,
creosote, and ethylene dibromide [136].
In
the
1950s, chlordane and other cyclodienes such as
heptachlor, aldrin, and dieldrin were marketed
as
soil tenniticides. These persistent and
inexpensive organochlorines, especially
chlordane, dominated the tennite control
industry for three decades
as
the main treatment
for subterranean termites. Environmental
persistence and public health concerns over
chlorinated hydrocarbons, however, lead to
their withdrawal from the market in the mid-
1980s. Currently, one organophosphate
(chlorpyrifos), four pyrethroids (permethrin,
cypermethrin, bifenthrin, and fenvalerate), and
one nicotinoid (irnidacloprid) are marketed
as
soil termiticides for the pest control industry in
the United States [60]. Cyclodienes and other
more potent biocides such
as
sodium arsenite
are still being used in other countries for
subterranean termite control, but the use
of
these products is increasingly restricted.
440 CHAPTER 20
Table
I.
Summary
of
detection, prevention and remedial control measures. Efficacy
of
some measures may not
be
supported
by
scientific data, and local availability
of
a given treatment may vary.
Subterranean termites
Detection Visual
Foraging tubes, damage, dispersal flights (imagos,
wings)
Non-visual
Acoustic emissions, sound amplifier, metabolic
gases, moisture, canine olfaction
Prevention Chemical treatments
Soil insecticide barrier
Remedial
control
Organophosphates, pyrethroids, nichotinoids,
organochlorines
Pyrethroid-impregnated polymer barrier
Wood
Impregnation
Chromated copper arsenates (CCA), coral tar
creosote, pentachlorophenol paste, disodium
octaborate tetrahydrate (DOT)
Non-Chemical
Physical barrier
Sized particle barriers, stainless steel barriers
Monitoring program
Termite-resistant wood
Construction
practices
Removal
of
wood debris, correct moisture problem
Barrier
treatments
Soil insecticide barriers
Trenching, rodding, and drill-and sub-slab injection
(organophosphates, pyrethroids, nichotinoids,
organochlorines)
Local
or
"spot" treatments
Chemical
Wood surface (aqueous DOT)
Wood injection
Aerosol (chlorpyrifos)
Dust (asenical, silica gel, chlordane, carbamates),
Liquids (organophosphates, pyrethroids,
nichotinoids, organochlorines)
Non-Chemical
Wood surface (electrocution, microwave)
Wood injection (nematodes, ftmgi)
Infested wood replacement
Population control
BiolOgical
control
agents
Fungi, nematodes
Metabolic inhibitors
Mirex, hydramethylnon, sulfluramid
Insect
growth
regulators
Juvenoids (methoprene, hydroprene, fenoxyarb)
Chitin synthesis inhibitors (hexaflumuron ,
diflubenzuron)
Drywood termites
Visual
Fecal pellets, damage, dispersal flights (imagos,
wings)
Non-visual
Acoustic emissions, sound amplifier, metabolic
gases, canine olfaction
Chemical treatments
Wood
Impregnation
Chromated copper arsenates (CCA), coal tar
creosote, pentachlorophenol paste,
disodium octaborate tetrahydrate (DOT)
Chemical
Surface
Applications
Organophosphates, organochlorines, pyrethroids
Residual Alate
Toxicants
Silica gel
or
drione, DOT
Non-Chemical
Alate
exclusion
Traps (light, sticky), caulking, paints, coatings,
Insect screening
Termite-resistant wood
Non-wood
construction
Whole-structure treatments
Chemical
Fumigation (methyl bromide,
SUlfuryl
fluoride,
CO
2 synergism)
Non-Chemical
Heat
Compartmental treatments
Non-Chemical
Heat, cold, liquid
N2
Local
or
"spot" treatments
Chemical
Wood surface (pentachlorophenol paste,
Lindane/oil, aqueous DOT, d-Limonene)
Wood injection
Aerosol (chlorpyrifos)
Dust (asenical, silica gel, chlordane, carbamates),
Liquids (spinosad, DOT, DDT)
Gallery fumigant (ethylene dibromide,
trichlorobenzene, d-Limonene)
Non-Chemical
Wood surface (electrocution, microwave)
Wood injection (nematodes, ftmgi)
Infested wood replacement
20.
TERMITES
AS PESTS OF BUILDINGS
2.1.2
Physical barriers
Because
of
the concern over the
environmental impact
of
termiticides, physical
barriers
are
getting more attention in recent
years. Two physical barrier types, uniform sized
particles and stainless steel screening
are
commercially available. More than
40
years
ago,
barriers composed
of
soil particles that
are
too large
for
termites to displace with their
mandibles, yet are too small
for
termites
to
pass
between, were discovered to stop termite
penetration
[23].
This observation was later re-
discovered [134], and confIrmed
[71,
106, 118.
125].
Currently, the gravel barrier (BTB,
Basaltic Termite Barrier) is accepted in Hawaii
as
a pre-construction treatment option
[43].
Field studies demonstrated that stainless steel
mesh barriers (TERMI -
MESH®)
withstood
intensive foraging activities
of
several termite
species under fIeld conditions
[43,
66].
As
the
combination
of
physical and chemical barrier,
polymer sheets impregnated with insecticides
are also being used in Australia
[68].
These
barriers can be used most effectively
as
continuous horizontal barriers during pre-
construction installation.
2.1.3 Population management
The objective
of
population management
approaches is
to
protect structures by
suppressing or eliminating subterranean termite
populations nearby. Early
on,
slow-acting
toxicants such
as
arsenic dust were applied into
foraging tubes in
an
attempt to impact colony
populations [137]. Dechlorane (rnirex), a slow-
acting toxicant, was proposed
for
the
elimination
of
isolated populations
of
the
eastern subterranean termite,
R.
flavipes in
Canada
[29].
Subsequent studies using rnirex
bait blocks indicated that a continuous
placement
of
toxic baits might have suppressed
foraging activity
of
Reticulitermes species
[11,
27,28,
82],
but the effects
of
baiting on colony
populations were not assessed. Lack
of
information
on
the foraging populations
of
441
subterranean termites, especially on the
interconnection between baited sites and
evaluation sites, hindered such assessment
[120].
Realizing the importance
of
delineating
colony foraging boundaries in his attempt to
control
Co.
formosanus populations using
entomopathogenic fungi, Lai
[62]
developed the
mark-recapture technique using the dye marker,
Sudan Red
7B.
Together with the radioisotope
140La
previously used [84], dye markers such
as
Sudan Red
7B
[38,
41,
58,
62,
112]
and Nile
Blue A
[108,
126,
128]
have been used
to
delineate foraging territories
of
subterranean
termite colonies. The presence
of
marked
termites was used to confmn the
interconnection
of
monitoring stations, and the
area encompassing the interconnecting stations
was considered part
of
a colony's foraging
territory. When a control method such as a
slow-acting bait was applied within the colony's
foraging territory, its efficacy against the
colony population could be objectively
evaluated by measuring changes in foraging
activity from untreated stations located within
the foraging boundary
of
the target colony
[120].
F
or
all practical purposes, therefore, a
subterranean termite colony can be defIned
as
"a group
of
termites sharing interconnected
foraging sites" [122]. This defInition precludes
the complications due to colony budding:
namely that the budded population is
considered
an
independent "colony" once
foraging sites have been separated. Population
control at the colony level thus targets an
interconnected foraging group.
To impact the population
of
a subterranean
termite colony that may contain 100,000
to
>1,000,000 foragers with foraging distances
extending
up
to
100
m from the colony center
[41,
112,
128],
the active ingredient
for
incorporation into a bait must be slow-acting
and non-repellent [123]. There are three groups
of
candidates that may satisfy these criteria:
some biological control agents, metabolic
inhibitors, and insect growth regulators.
442
2.1.4 Biological control agents
There are numerous laboratory studies that
demonstrate the pathogenicity
of
biological
agents such
as
the entomopathogenic nematode,
Neoaplectana carpocapsae Weiser
[35],
or the
fungi, Metarhizium anisopliae Sorokin and
Beauveria bassiana (Balsamo) Vullemin
[63].
Field trials using these biological agents,
however, have been generally unsuccessful
[62,
76].
To
date, only Hanel
[48]
was able to
successfully trigger
aM.
anisopliae epizootic in
colonies
of
an Australian mound-building
termite, Nasutitermes exitiosus (Hill). Because
termites are known to be repelled by pathogenic
fungi [77], discovery
of
non-repellent strains
of
some fungi species may be the key for
successful control
of
subterranean termite
populations [109]. Indeed, Milner et
al.
[77]
demonstrated that colonies
of
mound-building
termites could be eliminated by applying such
strains
of
M.
anisopliae.
2.1.5 Metabolic inhibitors
Metabolic inhibitors which have been used
in baits include borates
[33,
39,
59], dechlorane
(mirex)
[27,
28, 29,
82,
84], hydramethylnon
[85,
123],
A-9248 (diiodomethyl para-tolyl
sulfone) [113], and sulfluramid
[51,
114,
117].
In field evaluation studies using metabolic
inhibitors such as hydramethylnon
[85,
127],
A-
9248
[127]
or
sulfluramid [129], foraging
activities and/or populations
of
target colonies
were reduced but not eliminated.
2.1.6 Insect growth regulators (IGRs)
Two classes
of
IGRs, juvenoids (juvenile
hormone analogs or JHAs, and juvenile
hormone mimics or JHMs), and chitin synthesis
inhibitors (CSIs), have been tested
on
termites.
The gradual and cumulative mode
of
IGRs'
action makes them promising candidates
for
incorporation into baits.
Juvenoids. For most insect species, juvenile
hormone (JH) is responsible
for
retaining the
CHAPTER 20
immature forms, but JH also regulates soldier
formation in termites
[64,
73,
74,
75].
Because
the soldier caste is dependent
on
workers for
feeding, it was suggested that JHAs' potential to
induce excessive soldier formation may lead to
the nutritional collapse
of
the entire termite
colony
[50,
52,
53].
A literature review [116]
showed that JHAs were more likely
to
induce
significant soldier formation for termite species
that contained lower natural soldier proportions
(e.g., 1-2%
for
Reticulitermes spp.) than for
species with higher proportions (e.g., 10-20%
for
Coptotermes spp.); a view suggested earlier
[65].
Indeed, field trials using JHAs such
as
methoprene and hydroprene against
Prorhinotermes simplex (Hagen) (6.9-22.2%
soldier proportion, [50]) failed to yield an
increase in soldiers or a colony decline [54].
When another JHA, fenoxycarb, was used
against field colonies
of
Reticulitermes species,
an
increase
of
presoldiers and soldiers and a
subsequent decline in their foraging activity
was observed
[57].
Chitin synthesis inhibitors. Chitin
synthesis in insects, other arthropods and fungi
is inhibited by derivatives
of
benzylphenyl
ureas
[47].
In termites, ecdysis inhibition by
diflubenzuron (Dimilin) was first demonstrated
in Heterotermes indicola (Wasmann) and
Reticulitermes jlavipes
[19].
Subsequent testing
with diflubenzuron
on
field colonies
of
Microcerotermes spp., however, provided
inconclusive results
[30].
Laboratory studies
indicated that chitin synthesis inhibitors (CSIs)
such as diflubenzuron
[119]
or lufenuron
[121]
inhibited ecdysis
of
R.
jlavipes, but caused
virtually no effect on
Co.
formosanus. To date,
only one CSI, hexaflumuron, is known to cause
significant ecdysis inhibition
of
a wide range
of
economically important subterranean termites
species, including Reticulitermes, Coptotermes,
and Heterotermes
spp.
[119,
121].
Currently, hexaflumuron is incorporated in a
bait matrix
for
use in a monitoring/baiting
program, commercially known
as
the
Sentricon®
system [122]. Stations containing
monitoring devices
are
first installed in soil
20.
TERMITES
AS
PESTS OF BUILDINGS
surrounding a structure (Figure
1).
When
tennites are detected in the stations, the
monitoring devices are replaced with tubes
containing hexaflumuron bait. Following bait
application and when termite activity is no
longer observed in the stations, bait tubes are
replaced with monitoring devices to reinitiate
the monitoring program.
Thus
far,
16
field studies reported complete
cessation
of
tennite activity following
application
of
hexaflumuron baits in 47
of
53
(89%) baited colonies
of8
tennite species in the
United States, Australia, Japan, and France
[10,
12, 14,
18,34,44,46,67,
72,
85,
111,
130,
131.
133,
135,
142].
Of
the 6 failures, 5 were
accounted
for
by a single study
[85].
Direct
evidence
of
colony elimination was provided
when tennite mounds
[67]
or nests
[142]
were
excavated following bait applications, but in
most other studies in which indirect methods
such as mark-recapture were used, it was highly
likely that the baited colonies were eliminated
as
well.
2.1.7
Other
control options
Other options
for
subterranean tennite
control include wood treatments and cultural
control such
as
removal
of
wood debris, and
avoiding accumulation
of
water (leaky roof,
plumbing, condensation, rainfall, irrigation,
etc.) in and around structures. Building codes
require pressure-treated wood (creosote,
pentachlorophenol, inorganic salts such
as
chromated copper arsenate, etc.) at the wood-
soil interface; primarily to prevent fungal
decay.
If
present, subterranean tennites are
capable
of
by-passing the treated wood to infest
untreated wood. Local or "spot" treatments are
available to control the active infestation
of
subterranean tennites in a structure (Table
1),
but such treatments usually miss the majority
of
subterranean tennite populations in or near a
structure, and
are
merely temporary. Other
options include destruction
or
removal
of
accessible nests
or
mounds. Recently, use
of
borates
for
surface spraying
of
wood in service
has become popular for control
of
subterranean
443
tennites. However, surface treatment with
borate, even at the label rate, did not protect
wood beneath the treated surface from field
populations
of
Co.
formosanus
[40].
2.2
Control
of
drywood termites
More methods have been developed,
marketed, and ultimately deployed
to
control
drywood tennites than any other structural or
household pest (Table
1).
There are several
reasons
for
this.
One
of
the greatest
determinants
of
treatment choice, and often
one
of
the most uncertain and difficult
to
ascertain,
is the location and extent
of
a drywood tennite
infestation. After many recolonization cycles, a
structure may contain many infested wooden
members, each infested by one or more
colonies. Accessibility
to
each or all colonies
may
be
limited.
In
such a case, a whole-
structure treatment such
as
fumigation or heat
treatment may be the only viable means
of
eradication.
In
other situations, infestations may
be limited to relatively accessible areas and can
be treated with local methods. The scope
of
available drywood tennite control treatments is
shown in Figure
2.
Treatment cost, aversion
to
chemicals
by
the property owner, convenience,
chance
of
success, and local availability
of
a
given treatment all dictate which method will
be employed.
2.2.1 Detection
of
drywood termites
Before any treatment
for
drywood tennites
can be recommended, the viability and extent
of
the infestation must be determined. Better yet,
pinpointing the exact location
of
termites within
their gallery system will ensure more effective
control
if
a local treatment is
to
be applied. The
ability
to
detect termite activity also allows the
pest control operator to monitor the success or
failure
of
a given treatment. Drywood tennite
detection relies mostly
on
wood probing and
visual inspection. Canine olfaction and a variety
of
sound (electronic stethoscope) and metabolic
gas/water vapor detection devices
[69]
have
been used to locate termites.
444
Bora'.
Figure
2.
Drywood termites infest structures during
dispersal flights. Once alighted and paired, imagos select
nesting sites
in
wood.
Preventative treatments with
chemical and physical barriers
and
surface-treated or
preserved wood can reduce or prevent the potential for
colonization.
How
drywood termites
are
controlled in
structures
may
depend on the extent
and
location
of
the
infestation(s). Whole structure treatments with fumigants
and
possibly heat,
are
useful when infestations
are
wide-
spread
and
mostly inaccessible. Compartmental treatments
can be applied to large (heat)
or
small (cold) portions
of
the structure that encompass infested
wood.
Local
treatments include methods that
are
applied directly to
the
accessible wood surface such
as
microwaves,
electrocution,
or
some chemicals applied
to
raw
wood.
Wood
injection treatments (drill and treat)
are
applied
locally
and
impart termiticide directly into termite
galleries inside
raw
or painted
wood.
Some
gallery
treatments require only minimal accessibility to the
infestation.
Each method has its shortcomings: inherent
difficulties in using dogs
[69],
interfering
audible background sounds, sporadic methane
production [138], or insufficient moisture
production by drywood termites. New
technological advances in filtration
of
background acoustics and amplification
of
termite-generated acoustic emissions, however,
have improved the prospect
of
detecting
termites and other wood-feeding insects. The
feasibility
of
using a hand-held, battery-
powered acoustic emissions (AE) detector to
CHAPTER 20
locate and monitor termites in wood has been
demonstrated
[98].
This device offers a reliable
method
for
localized, non-destructive detection
of
termites.
An
inspector would simply place a
sensor
on
the surface
of
wood
he
suspects to
harbor drywood termites based upon lists
[83,
107]
of
existing visual evidence such as pellets,
kick-out or emergence holes, or surface
damage. The
AE
detector can also be used to
evaluate the efficacy
of
various chemical
treatments in the field [101].
2.2.2 Prevention
Prevention
of
drywood termite colonization
follows two approaches: making wood
unpalatable to termites or preventing
establishment
of
inCIpIent
colonies by
intoxicating or excluding winged and dealated
reproductives during their short dispersal forays
and nuptial chamber constructions.
Unpalatability includes using termite-resistant
lumbers
[94]
or susceptible lumber treated with
wood preservatives
[56,
91,
103].
Because
dispersing imagos seek dark habitation after
flight, attics, voids in walls and furniture, and
crawl spaces
are
often
foci
for
colony
establishment. Silica aerogel dust
was
recommended as desiccating toxicant
for
attic
and wall void treatments to kill alates
[24]
and
was toxic in the laboratory against
Cr.
brevis
[78].
However, colonies could establish
on
wooden blocks that were only partially dusted
with silica gel/pyrethrum [103]. Disodium
octaborate tetrahydrate (DOT,
TIM-BOR®)
dust
or aqueous solution, however, completely
prevented block colonization.
No
work has
been done
on
the efficacy
of
alate exclusion
methods such as screening and other exclusion
devices
for
attics, foundations, and windows;
or
roofmg material, caulking, or wood coatings.
The efficacy
of
light or sticky traps is also
unknown.
2.2.3 Whole-structure control
Structural fumigation with methyl bromide
(BROM-O-GAS®)
or sulfuryl fluoride
20.
TERMITES
AS
PESTS OF BUILDINGS
(VIKANE®),
administered per label directions,
will completely eradicate drywood termites
from a structure
[13,
70,
81, 95,
101,
110].
Therefore, fumigation has been the treatment
of
choice when drywood infestations are extensive
or difficult to access or delineate. Early
fumigants included most notably, hydrocyanic
acid
[55]
and acrylonitrile. In Australia,
structural fumigations with methyl bromide
were used in
an
eradication program against
Cr.
brevis
[87].
Although fumigated buildings were
cleared
of
Cr.
breViS,
new infestations
in
other
buildings continued
to
surface [88], owing to
the futility
of
such eradication attempts. The
inherent disadvantage
of
fumigation is the lack
of
residual protection.
In California, where fumigation is often
required prior to closing the escrow
of
infested
structures, about 150,000 dwellings are
fumigated annually. However, concerns about
human exposure to fumigants has spawned new
stringent laws governing structural fumigation
practices in California
[2],
and new restrictions
will likely
be
adopted by other States. Methyl
bromide has been recently implicated in
atmospheric ozone depletion and is scheduled
for phasing out by the year 2005 under United
States Environmental Protection Agency
guidelines
[7].
The quantity
of
fumigant used
to
treat an average size home, approximately 5-10
kg, also puts structural fumigation at risk
as
this
amount greatly exceeds the active ingredient
requirements for most other pest control
practices.
Carbon dioxide
(C0
2) has long been known
to enhance the toxicity
of
fumigants to control
insects infesting raw food commodities [15];
however its use was not developed for
structural fumigation until recently. In 1993,
California and Florida approved a structural
fumigant label under the MAKR brand for the
application
of
methyl bromide at 8 mg/liter in
admixture with
CO
2 at
176
mg/liter (10% v/v)
for a 16-24 hour exposure
[3].
Laboratory
studies revealed that 5-10%
CO
2 combined with
methyl bromide or sulfuryl fluoride appreciably
synergised the toxicities
of
both fumigants
against
1.
snyderi psuedergates by up to about
445
1.8-fold, equal to a reduction in required
fumigant concentration
of
about 45% [100].
The proscription
of
some localized
chemicals (e.g. arsenic dusts, ethylene
dibromide, pentachlorophenol, etc. see Table
1)
in most developed nations has intensified the
reliance on structural fumigation for drywood
termite control, especially in the United States,
where the cost is tolerated by necessity.
Because fumigation is technically complicated
and expensive, and regulatory concern about
the practice is mounting (California Structural
Pest Control Board, [93]), there is a need to
develop effective alternative treatments. In the
United States, structural fumigation is the only
method
of
pest control that occasionally results
in accidental human mortality (e.g., [86]).
2.2.4 Compartmental control
In recent years, heat treatment
of
structures
has been promoted
as
a non-chemical means
of
drywood termite eradication
[32].
The thermal
limit
for
1.
minor was estimated at
49°C
for
33
minutes
[32]
to
52°C
(time not specified, [91]).
Heating a
154
m3 building containing
1.
minor-
infested boards until wood temperature
of
selected boards reached
50°C
for at
ca.
1 hour
resulted in termites surviving only in a
few
infested boards adjacent to the concrete
foundation (heat sink) where wood
temperatures were not recorded [70]. 100%
mortality was obtained when
Cr.
brevis and
1.
snyderi pseudergates were exposed to
48°C
for
10
minutes and
50°C
for
15
minutes,
respectively [102]. In additional tests with
C.
brevis, relative humidity and acclimation
to
warmth
(35°C,
10
days) had no effect on heat
tolerance. 100% mortality
of
1.
immigrans
(Light) was obtained
at
46°C
exposures for 30
minutes [139], while gradual heating from
28°
at
0.7°C/min resulted irreversible heat shock to
N.
connexus Snyder,
1.
immigrans, and
Cr.
brevis at
51°C.
Ambient
air
and internal wood
temperatures were monitored
at
9 field sites in
Hawaii during commercial heat treatments for
Cr.
brevis [140]. Air temperatures ranged from
52-85°C (0.04-1.44°C/min) and wood
446
temperatures from 39.2-72.3°C in treatments
of
building compartments and required 15-300
minutes to reach the wood target temperature
of
49°C,
[140], however termite mortality was not
evaluated. At present, fumigation, and possibly
heat treatment, although expensive and
inconvenient, are the only viable means
of
whole-structure, single-treatment eradication
of
drywood termites.
Low temperature spot treatments by
introduction
of
liquid nitrogen
(N2)
in the
proximity
of
infested wood members
are
commercially available. Unlike heat treatments
that can accommodate large volumes (=500
m\
cooling with
N2
is suited only
for
small
compartments (e.g.
<1
m3) such
as
wall voids or
similar sized areas where infestations can be
enclosed by insulation blankets
[26,
31].
98%
mortality
of
1.
minor was obtained when
N2
was
administered at
123
kg/m3
[70], while
pseudergates
of
1.
minor and
1.
snyderi
succumbed to momentary exposures
of
-21°C
and -17°C, respectively, when temperatures
were lowered at I°C/min
[92].
To achieve these
temperatures within
10
minutes throughout
wood framing in 2.4-m-high by O.4-m-wide
wall voids,
N2
was introduced at the top
of
the
void at a minimum rate
of
1.8
kg/min. Wall
insulation hinders the cooling process
[92].
Because the
N2
can displace air, oxygen
concentrations must be monitored
for
safety.
2.2.5 Local control
Local or "spot" treatment for drywood
termites is recommended when the extent
of
an
infestation can be delineated and is at least
partially accessible. Unlike whole-structure or
compartmental treatments, these are applied
directly to the infested wood members. The
lower cost and greater convenience
of
some
local treatments, like drill-and-treat
applications, makes them attractive choices.
Chemicals registered for spot application can be
classified
as
to mode
of
application: wood
surface or intragallery injection termed "drill
and treat"
[83].
DOT formulations are currently
being used in aqueous or dust
(TIM-BOR®),
CHAPTER 20
aqueous glycol
(BORA-CARE®),
or foam
formulations
as
unpainted wood-surface
treatments
for
both control and prevention
of
drywood termites. Until its prohibition in the
United States, pentachlorophenol, applied in a
petroleum-based paste (Woodtreat-TC), was the
treatment
of
choice
on
bare infested wood
surfaces [21].
Although published data are lacking, the
practice
of
injecting ethylene dibromide (EDB)
by itself
or
with a residual chemical such as
chlordane, DDT, or other organochlorine, was
used
as
a drill-and-treat formulation
[21].
The
EDB
volatilized throughout the gallery system
as
a local fumigant. The organochlorine
additive was intended to give long-term
residual protection. Trichlorobenzene was
suggested
for
use in the same manner as
EDB
[107], but like the materials above, is no longer
registered for use in the United States.
It
has
been shown that insects are susceptible to the
gaseous phase
of
a number
of
non-halogenated
volatile organic compounds based on natural
products
[20]
and at least one commercial
product (Power
Plant®)
consists
of
d-limonene
[5].
Paris green or copper aceto-arsenite dust,
when injected into galleries at I-meter intervals,
was shown
to
successfully control extensive
infestations
of
drywood termites in utility poles
[90].
Only 1 g
of
arsenic dust was sufficient
to
treat a large infestation. The efficacy
of
Paris
green was attributed to its slow activity and
non-repellent quality against termite workers
which, when contaminated, would actively
spread the toxicant among uncontaminated
nestmates. Any nestmates foraging in treated
galleries would, likewise, be contaminated. The
success
of
field tests with Paris green dust
against
1.
minor was also noted [105]. A
formulation
of
35% calcium arsenate (KALI-
DUST) was a mainstay product in drill-and-
treat applications
for
many years. Working with
and injecting this dust was messy and exposed
the pest control operator
to
the hazardous
toxicant. Arsenic dusts, because
of
their acute
mammalian toxicity and carcinogenicity, are no
20.
TERMITES
AS
PESTS OF BUILDINGS
longer registered for pest control in the United
States.
Many chemicals such as chlorpyrifos (PT-
270 Dursban), cyfluthrin, and safrotin currently
used in drill-and-treat applications in the United
States rely on acute contact toxicity. Such
insecticides may be repellent or deterrent to
drywood termites [101]. Drywood termites in
untreated wood galleries might avoid foraging
in treated portions
of
their gallery system, and
thus survivors might reinstitute colony
development and redirect damage elsewhere in
the wood members. Control success with these
compounds is also related to treatment coverage
which, in tum, depends on the accessibility
of
infested wood. Therefore, control rendered by
such drill-and-treat applications may be limited
to small areas because only termites in
chemically-treated galleries are certain to be
contacted by the toxicant. Spinosad SC has
emerged as a superior compound to
organophosphate and borate treatments for
drywood termite control [101, 103]. As a 5,000
ppm aqueous solution, spino sad SC dries as a
non-repellent, slow-acting residue that has the
termiticidal characteristics
of
arsenic dust, but
is an environmentally safe fermentation product
[4].
Microwave and electrocution treatments for
local control
of
drywood termites have been
commercialized in the United States.
Inconsistent control
of
1.
minor was achieved
with microwave (high frequency
electromagnetic energy) applications applied at
700W [70]. In this study, infested wood
members were twice-treated for 8 minutes in
30-cm increments. The equipment provides no
measurement
of
dose and is large, heavy, and
poorly maneuverable, making treatment in
some locations impossible.
A device called the "electrogun" produces a
high-voltage, high frequency electric current to
electrocute drywood termites in their galleries
[22]. This produced 89-95% mortality to
1.
minor in boards that were fitted with metal pins
and treated with the electrogun probe for
between
1.5
minutes and
1.
75
hours [70]. There
was 100% mortality in a laboratory evaluation
447
of
the electrogun against the Australian species
Cr.
primus (Hill), however, bioassay blocks
were small (15 x
10
x 4 cm) and treatment time
lengthy (7-8 minutes) [16]. At this rate, it
would take 15-17 hours to treat a typical 2.1x
0.9 m door. As noted
by
Lewis and Haverty
[70], efficacy
of
this method is excessively
technique driven. Although maneuverable, the
electrogun provides no measurable dose
parameter and is subject to interference by
metal and concrete.
At present, drywood termites have been
elusive targets for biological control. A field
trial with Heterorhabditis sp. nematodes on the
Sri Lankan dampwood termite, Glyptotermes
dilatatus (Bugnion & Popoff), suggests that
control is possible by intragallery injection
of
nematodes in moist woody stems
of
infested tea
plants [17]. However, the extremely
dry
conditions
of
typical structural infestations
would present a much greater challenge to
nematode survival and movement (R. Giblin-
Davis, personal communication) The
entomophagus fungus,
Metarhizium.
anisopliae
(Strain ESC
1)
is registered for drywood termite
control [6], however, lack
of
moisture may also
reduce virulence.
3. FUTURE PERSPECTIVES
The growth
of
human populations has
spawned an increase in the production and
transport
of
structural lumber and wood
products to meet construction demands [25].
Such activities will continue to foster
conditions that cause susceptible wood
materials to be exposed to termites and will
further the spread
of
pest species
[1,
9,
96, 104,
132, 141]. Therefore, an increase in the
worldwide damage from termites and a need to
prevent or control these pests can be
anticipated.
3.1 Subterranean termites
The currently available termiticides such as
organophosphates or pyrethroids are less
448
persistent than the cyclodienes. Despite such
shortcomings, soil tenniticide application will
continue because
of
their mandatory use in the
pre-construction market. Liquid tenniticides
will also continue to play a vital role in
remedial treatments, where their application has
an immediate effect in mitigating tennite
activity. For the pre-construction barrier
application, physical barriers
[66,
67]
or
pyrethroid impregnated polymer barriers
[68,
122]
may replace current liquid insecticides.
The role
of
such safer barrier techniques in the
future
of
subterranean tennite control may
depend
on
their acceptance
by
the construction
industry and willingness
of
buyers to appreciate
and absorb the cost.
In comparison with the conventional liquid
insecticide applications, the monitoring-baiting
program such as the Sentricon system is a
tangible system that is more target specific,
uses less pesticide (e.g., 1 gram
of
hexaflumuron versus 5-10 kg soil insecticide),
is less intrusive (no drilling
of
slab floors), and
can provide long-term protection
for
as
long
as
the monitoring program is instituted. The
system, however, is also more expensive, time-
consuming, and labor and technique intensive.
Technology development such
as
acoustic
emissions and other detection devices may aid
to reduce the cost
of
monitoring that is
currently the most labor intensive. Discovery
of
other slow-acting compounds and revised bait
formulations may improve the baiting
efficiency. But, most
of
all, a better
understanding
of
physical, chemical, and
biological factors affecting foraging and food
finding behaviors
of
subterranean tennites will
significantly improve the monitoringlbaiting
program so that it may become more acceptable
to tennite control industry.
3.2 Drywood termites
In future, the remedial control
of
drywood
tennites will rely more on local treatments and
less on whole structure methods (Table
1).
This
will be, in part, due to improvements in local
treatment efficacy and because
of
increasing
CHAPTER
20
regulatory control
of
the fumigation industry
from the standpoint
of
air quality and hazard to
humans. Fumigations will also yield, in part, to
the use
of
heat
as
techniques in heat distribution
and heat damage prevention improve.
The greatest area
of
development has and
will continue
to
be with intragallery treatments
of
drywood tennite infestations. Acoustic
emissions detection will allow superior and
non-invasive delineation
of
infestations to
pinpoint treatment areas and to confirm the
treatment efficacy. Compounds like spinosad
will allow eradication
of
drywood tennite
colonies, even when only partially accessible
[101,
103].
Such treatments can be
accomplished with minimal equipment,
inconvenience, odor, and treatment time; and
with no environmental hazard. Such treatments
are well suited for untapped markets in
developing countries.
As more is understood about the foraging
behavior and dynamics
of
drywood tennites,
active ingredients and their formulations can be
optimized
for
maximum exposure, transfer, and
feeding. Development
of
preventative
treatments
[103]
will offer protection from
drywood tennite infestation that can be
installed
ill
new
as
well
as
existing
construction.
ACKNOWLEDGMENTS
We
thank
1.
Perrier (University
of
Florida)
for
figure illustration, and
B.
Pemberton
(USDA-ARS) and
F.
B.
Howard (University
of
Florida)
for
reviewing the manuscript. This
article is Florida Agricultural Experiment
Station Journal Series
No.
R-06763.
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