Preserving Our History: Freezing Infested Materials

by Patrick Kelley, ACE

After discovering that insects are eating away at your personal goods or museum objects, you are faced with the dilemma of how to get rid of the live bugs. Options include a wide range of treatments such as anoxia (low oxygen), inert gas, carbon dioxide, detailed vacuuming and exposure to heat. One of the most popular and easiest methods of treatment though is to simply freeze the items in question. This method is non-toxic, time efficient and does not entail extensive staff training. The museum community’s use of freezing to kill a multitude of common museum pests has been quite successful. Some museums in the United States have treated thousands of objects with low temperatures and have reported no damage on the types of objects that had warnings previously associated with exposure to cold temperatures. Freezing insects to death can be one of the best treatment options.

The general principle to follow is to expose the objects to temperatures as low as possible, as quickly as possible for as long as possible. The guidelines below will kill the majority of museum pests.

The formation of ice crystals within the bodies of the insects is what causes the killing effect. The reason why many insect species survive through icy winters is because they have time to acclimate their bodies to the cold. The insects increase the concentration of glycerol and sugars in their tissues as the temperatures slowly drop. This has the effect of an anti-freeze within their bodies and it prevents the formation of ice crystals. For this reason, it is best to hold the object that you are going to freeze at room temperature for at least one week prior to the exposure to cold. The thermal shock of the quick temperature drop catches the insects unaware and allows the temperatures to have a lethal effect.

General Guidelines for a Low Temperature Treatment:
– Use a freezer that can maintain a temperature of -20°F (-29°C).
– Objects should be placed in sealed bags to reduce ice or condensation damage.
– Sensitive items can be wrapped in tissue paper before being placed in the bags.
– Hold the items at the low temperature for a period of one week or longer.
– Large wooden items or dense materials should be left frozen for longer periods.
– After removal from the freezer, the items should remain in the sealed bags to prevent condensation.
– Once the items reach room temperature for +24 hour period, they can be removed from the bags.
– Items become temporarily brittle at low temperatures, so handling should be kept to a minimum until the items return to room temperature.

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Freezing insects to death can be one of the best treatment options.

References for the material used in this article include the following:
Strang, Thomas, J.K., “Controlling Insect Pests With Low Temperature.” CCI Note 3/3, Canadian Conservation Institute, 1997.
Integrated Pest Management Working Group, “Low Temperature Treatment Fact Sheet.” [Accessed 2, November, 2010] Available at http://www.museumpests.net/treatment.asp.

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