In reply to Jim Croft's inquiry on the use of diatomaceous earth or
silica gel for pest control, here are references for two recent reviews of
these materials.
 
Quarles, W. 1992. Diatomaceous Earth for Pest Control. The IPM Practicioner,
14(5/6):1-11.
 
Quarles, W. 1992. Silica Gel for Pest Control. The IPM Practicioner, 14(7):1-11.
 
        These papers review: mode of action, efficacy after different
application methods and concentrations, humidity and efficacy, formulations
with other insecticides, control failures, health and safety.
 
        While abrasion is often cited as the critical damage, oil absorbtion
from the cuticle is actually quite important, if not dominant, for increasing
water loss in the organisms.  This effect is influenced by the properties of
the waxy epicuticle, rate of dust uptake, absorbtive capacity and particulate
size of the dust (see Quarles).
 
        It is a common museum experience that the footprint of the lowest tier
cabinet supports a continuing source for reinfestation, and that there is often
a direct route through the cabinet fabric, either failed seals or cabinet wall
perforations for lock hardware and ventilation.  These breaches should be
eliminated.
 
        As the floor gaps are usually under a couple of millimeters, normal air
movement through the gap is less likely to get the dust airborne.  There are
likely to be electrostatic and other cohesive forces that increase the adhesion
of the dusts to the surfaces, making the settling velocity a worst case number.
 Dessicant dusts have also been tested with mild adhesive systems (see
Quarles).  If the dust kills the pest, or the pests avoid dust treated areas,
you win.
 
        If the material is blown into wall cavities, it is possible that cracks
on the inside wall could be a path for airborne irritant dust as there can be
significant air movement through cracked building fabric.  I know of a museum
currently applying dessicant systems in exterior and interior wall cavities,
and they are also ensuring floor and ceiling joints are caulked and electrical
outlets are sealed during drywall installation.  This latter action not only
reduces pest migration and harbourage, it increases the museums ability to
control moisture and temperature in the interior environment and lowers energy
cost.
 
        Avoiding a problem is often the best solution.  Narrow crevices should
be eliminated by elevation of cabinets on attached skids (earthquake mitigation
must be considered in the assembly) that provide easy access for periodic
sanitation procedures (e.g. vacuuming, mundane but very effective).
 
See:  Williams S.L. and McLaren S.B. 1990. Modification of storage design to
mitigate insect problems. Collection Forum, 6(1):27-32.
 
 
Tom Strang
Canadian Conservation Institute
1030 Innes Rd., Ottawa, Ontario, CANADA
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