Adult insects, their eggs, larvae, and pupae cannot survive in an oxygen-free atmosphere. How long will it take to reliably destroy any insects in your artefacts? As in most conservation concerns, the answer is: “It depends”.
The time needed to kill different species of insects depends on a number of variables (including oxygen levels, gas composition, temperature, relative humidity, and the species’ inherent resistance to low oxygen conditions). Most sources agree that given an oxygen level of less than 0.5%, temperature is the most important variable.
Below you will find some of the commonly available data and opinions on how long to treat your artefacts.
from Vinod Daniel’s Museum and Insect Pests: Prevention and Non-Toxic Control page 12 “…it is recommended that the time required for effective treatment in low oxygen environment (les 0.3% oxygen in nitrogen) at 55 % RH and 25 degrees C is two weeks.”
from The Feasibility of Using Modified Atmospheres to Control Museum Pests by Rust & Kennedy, published by The Getty Conservation Institute “The results showed that the time required to kill 100% of the insects varied among species and even among the developmental stages of a given species. For most insects tested, exposures of less than 72 hours were required to insure complete kill. Certain stages, such as eggs of cigarette beetles, may require up to 8-day exposures to insure complete kill. Preliminary tests indicated that the addition of CO2 to the nitrogen slightly decreased the exposure time required to kill the insects. However, if increased temperatures or decreased relative humidities could be tolerated by the objects, they would probably have a much greater effect than using CO2 and N2 mixtures in reducing exposure times.
from the Tokyo National Research Institute of Cultural Properties:(courtesy Mitsubishi Gas Chemical)
Highly Resistant Insects:
Cigarette beetle (Lasioderma serricorne)
Drugstore beetle (Stegobium paniceum)
Pbscent anobiid (nicobium hirtum)
Book-borer anibiid (Gastrallus immaginatus)
Brown powderpost beetle (Lyctus brunneus)
Recommended anoxic state duration: 3 weeks at 30 degrees C
Moderately Resistant Insects:
Black carpet beetle (Attagenus japonicus)
Varied carpet beetle (Anthrenus verbasci)
Recommended anoxic state duration:
1 week at 30 degrees C or 2 weeks at 25 degrees C
Weakly Resistant Insects:
German cockroach (Blattella gemanica)
Webbing clothes moth (Tineola bisselliella)
Japanese termite (Reticulitermes speratus)
Casemaking clothes moth (Tinea translucens)
Oriental siverfish (Ctenoiepisna villosa)
Firebrat (Therobia comestica)
Recommended anoxic duration:
1 week at 25 degrees C
Note that the times for treatment are halved for a 5 degree C (10 degree F) rise in temperature
You will find excellent information in the Getty Conservation Institute’s “Inert Gases in the Control of Museum Pests” by Charles Selwitz and Shin Maekawa. Below is an excellent chart listing insect mortality, originally from page 12 of the book.
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