Comparison of Treatment Methods
Treatment for insect pests
To 55–60°C: Exposure time depends primarily on thickness of the object. Consult IPM application guides. Enclose the object in a vapour-barrier bag or equivalent container to contain the pests and eliminate the risk of moisture content change during heating. Space-frames Footnote * may need dunnage (natural fibre sheeting) to increase moisture control, or supply moist, conditioned air during the treatment (commonly 15% RH over ambient levels). Heating methods include radiant space heating, forced air, and solar heat (Strang ).
Near universal efficacy against all insects. Universally available technology. Short turnaround time. Wide scale of proven application–from single objects to entire buildings.
Logistics of enclosure to ensure the necessary vapour barrier exists that will restrict change in moisture content and reduce heat loss, especially when treating large structures. Forced air circulation through air ducts and numerous monitoring points are necessary when treating large structures.
To −20°C for 2 weeks or −30°C for a week: Enclose the object in a vapour-barrier bag or equivalent container to contain pests, reduce moisture content change, and eliminate condensation risk on rewarming (Strang , ). Ensure that air flows completely around the object in the freezer chamber to prevent relatively warm "thermal bridges" forming. (When objects touch the chamber wall, they become part of the chamber's insulation, which allows heat to conduct into the objects from the outside.) As much as possible, carefully minimize the thickness of stacked, folded, or rolled objects before treatment so the largest surface area is exposed to cold air (e.g. books, carpets). Monitor temperature in the thickest object if possible to ensure the most effective temperature was reached. Consult IPM application guides.
Widely available technology; household freezers adequate. Winter cold in some locations is sufficient (−25°C or less) provided the object has had a month at human comfort temperatures (i.e. 22°C) before exposure to break insect dormancy. Effective against most museum insect pests that are not preconditioned by cool environments.
Logistics of enclosing large objects; however, a truck-body refrigeration unit can often be rented to do this. Minimum time in cold temperatures depends much more heavily on species characteristics than does heat treatment, so reducing exposure time is not recommended unless the species and its response are known.
Controlled atmospheres (low O2)
Expose objects for 1–3 weeks in atmospheres that contain very little oxygen (insects succumb most efficiently to anoxia at less than 0.1%, a common specification for control). Note that wood borers are the most tolerant to anoxia, requiring longer exposures. This fumigation technique uses compressed nitrogen (N2) gas in larger enclosures or oxygen scavengers in smaller volume enclosures. Oxygen barrier films are heat sealable and may only be used once or a few times. Flush out air from anoxic bags with moisture-conditioned nitrogen to conserve the oxygen scavenger. For a detailed application guide, consult Maekawa and Elert ().
Anoxia can be performed at room temperature (>20°C) in clear film or metalized film plastic bags. Long-term storage in anoxia bags significantly protects against reinfestation and other deleterious agents such as airborne contaminants, water, humidity swings, etc
Effectiveness is greatly reduced by moderately cool temperatures (less than 20°C). Anoxia in bags can be compromised by pinhole leaks or flawed seals. A few colorants are affected by a low-oxygen environment (chemical reduction), but this is mainly observed in long-term storage, not in the time span needed for pest control.
Controlled atmospheres (CO2)
Expose objects for 1–3 weeks in atmospheres that contain carbon dioxide (60–90% CO2 by volume induces fatal hypercarbia in a useful time period). Wood borers are commonly the most tolerant to hypercarbia, and require longer exposures. Contain CO2 in a rigid enclosure (fumigation chamber) or in a flexible enclosure designed for fumigation with CO2 (Warren ).
Carbon dioxide fumigation works in the presence of any remaining oxygen; therefore, fumigating large objects is generally not compromised by pinhole failures in the container, provided overall gas concentration and circulation are maintained.
Effectiveness is greatly reduced by moderately cool temperatures (less than 20°C). Carbon dioxide is registered as a fumigant and is an asphyxiant hazard to humans. Proper detectors and procedures are required. Carbon dioxide is a penetrating gas, affects mammalian physiology in low-percentage concentrations, and is easily adsorbed by concrete. Enclosure must be designed specifically for holding CO2. Appropriate life-safety measures must be observed. Longhorn beetles are very tolerant to elevated CO2.
- Footnote *
Objects whose construction creates a large ratio of open space to their components. When bagged, this results in a large air volume to be buffered.
CCI Technical Bulletin Nº 29.
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