Management of Drywood Termites: Past Practices, Present Situation and Future Prospects - Urban Insect Pests: Sustainable Management Strategies - page 138

(NPIRS, 2013). SF mode of action includes
the cessation of lipid catabolism and
glycolysis (Meikle et al ., 1963; Su and
Scheffrahn, 1986). Effi cacy in eliminating
infestations has been reported for SF for at
least eight species of drywood termites
(Stewart, 1957; Bess and Ota, 1960; Su and
Scheffrahn, 1986; Osbrink et al. , 1987;
Peters 1990; Scheffrahn and Su, 1992;
Thoms and Scheffrahn, 1994; Scheffrahn et
al. , 1995; Lewis and Haverty, 1996; Su and
Scheffrahn, 2000). There were more than
60,000 SF fumigations conducted in 2010
for four California counties alone (K. Boyle,
California Department of Pesticide Regu-
lation, 2013, personal communication).
The current regulation of SF structural
fumigation requires a pre-treatment de-
termination of an appropriate dosage based
on several biotic and abiotic variables and
that an entire building be sealed or enclosed
in tarpaulins to confi ne the gas. During pre-
treatment preparations the biotic and
abiotic variables that need to be considered
include target pest species, building
volume, soil type, soil temperature, wind
speed and quality of containment materials
(tarpaulins) (Stewart, 1966). Fumigants are
introduced as a gas via plastic tubing to a
space confi ned within the vinyl-coated
nylon tarpaulins that are wrapped entirely
around a structure and held together with
metal clamps. Water- or sand-fi lled plastic
tubes are also laid on tarpaulins at the base
of the structure to help prevent the fumigant
from escaping. Electric fans are used to help
the movement of fumigant to assist in
obtaining gas equilibrium throughout the
structure. Structural fumigation is highly
regulated due to risks of accidental human
mortality and undiscovered natural gas
leaks and build up underneath tarpaulins
that could potentially lead to ignition and
explosion (Su and Scheffrahn, 2000).
Aeration of a building can take several
days to reduce the SF concentration below
1 ppm before the fumigated structure is safe
for re-entry (CDPR, 2010). Certain materials
and commodities can retain fumigants for a
longer duration, up to 40 days (Scheffrahn
et al. , 1987). SF retention, described as the
ability of an object to release bound SF, is

referred to as desorption and is greatest for
unprotected fatty commodities (high oil
peanut butter and margarine) packaged in
'leaky' containers as well as polyester fi bre
and polystyrene insulation (Scheffrahn
et al. , 1987, 1992a,b). However, items
packed in double-nylon fi lm bags and
allowed aeration times of >7 h eliminated
all trace of SF for all foods and commodities
tested (Osbrink et al. , 1988; Scheffrahn et
al. , 1989a,b; 1990, 1994). The use of SF
affords no residual protection against the
threat of future infestation (Potter, 2011)
and recent atmospheric investigations have
labelled SF as a greenhouse gas (Sulback
Andersen et al. , 2009; Mühle et al. , 2009).
Two other whole-structure treatment
options - asphyxiant gases CO 2 and N 2 -
have been reported for drywood termite
control. Asphyxiant gases have been
examined and shown to be effective in
killing drywood termites (Paton and
Creffi eld, 1987; Delate et al., 1995; Rust et al. ,
1996). The investigation of asphyxiant gases
has been limited to laboratory or chamber-
sized containers more apt for museums,
commodities and quarantine situations. At
the present time large-scale use of asphyxiant
gases as a whole-structure option are not
technically feasible owing to the inability of
tarpaulins to contain the high concentration
of gas (>95%) needed and the long exposure
times >72 h required to kill drywood termites
(Delate et al. , 1995; Rust et al. , 1996).

Electricity

High voltage electricity (90,000 volts, <0.5
amps) has been commercialized and offered
for controlling drywood termites for at least
30 years in California (Ebeling, 1983; Lewis
and Haverty, 1996). The exact mode of
action is not known and is speculated to
involve the delayed killing of termite
intestinal protozoans (Ebeling, 1983). The
application of electric current to wood may
be achieved by waving the end of a device
over the surface or by drilling holes for
insertion of metal pins to aid transmission
of current below the surface (Lewis
and Haverty, 1996, 2001). Electric shock