Silica treatment for termite infestations

John Griswold <griswold<-a t->silcom< . >com> writes concerning drywood
termite eradication using colloidal silica injected into wood
structures, noting that a company claims the treatment results in a
highly successful residual effect against new infestations, etc.

I suspect that the "colloidal silica" is either amorphous precipitated
silica or silica aerogel, both of which have been used against dry
wood termites. The insecticidal qualities are typically attributed
to their large surface areas, pore diameters, and low sorptivity for
water. The most common commercial product is Dri-Die which has been
used for over 20 years. It is composed of amorphous silica gel (95%)
and ammonium fluosilicate (2%). Another common product is Drione. It
is also amorphous silica gel (40%), with the addition of pyrethins
(1%) and the synergist piperonyl butoxide (10%).

Both are relatively non-toxic. For example, the oral LD50 for
Dri-Die is reported to be approximately 7-8.8g/kg body weight. The
oral LD50 for Drione is reported to be greater than 5 g/kg in rats.
Both are listed in the EPA Toxicity Category III (Caution signal
word).

Both products have labels which specifically allow use for
_prevention_ of drywood termites in either existing buildings or new
construction. Neither product is labeled (at least in my book of
specimen labels) for the treatment of existing infestations. I
suspect the problem is largely getting the dust into the chambers and
in contact with the colony.

Are there other choices? Many termiticides labeled for subterranean
termites are also labeled for drywood termite eradication. In
general, however, you will find that termiticides are somewhat more
toxic. Another alternative is the use of a product such as Tim-Bor,
a disodium octaborate tetrahydrate, which is very effective against
a wide range of wood destroying pests. Physical removal is often an
appropriate treatment, since colonies are often (at least at first)
fairly small. Another approach which has been used with good effect
is heat treatment. A final option when large portions of a building
are infested tends to be fumigation.

While I would be reluctant to rely on dusts for eradication, they do
have tremendous potential to prevent infestations, especially since
the drywood termite typically requires unpainted or finished wood,
often found in attics or above garages, where there are large
amounts of unpainted wood.

I hope this helps, but would be happy to deal with any other issues that
might come up off-list. Best,

Michael Trinkley, Ph.D.
Director
Chicora Foundation, Inc.
PO Box 8664
Columbia, SC  29202-8664
803-787-6910

                                  ***
                  Conservation DistList Instance 10:85
                  Distributed: Monday, March 31, 1997
                       Message Id: cdl-10-85-003
                                  ***