Appendix 3: Chemical Treatments of Insects

The information contained in this appendix is based on a Technical Bulletin prepared by Dawson (1992).

Only a few representative chemicals are included in this appendix. Inclusion is not a recommendation for use, with a few commonly used pesticides included to alert readers to some of the potentially damaging effects of these products. Use this information as a guide when considering what action to take in response to insect attack on collections. Always remember to consult a conservator if in doubt about the impact of a particular treatment on objects in a collection. Also check with local authorities regarding the application of any large scale pest treatment to ensure compliance with regulations and laws regarding the use of potentially toxic chemicals.

Fumigants

As long as the concentration and exposure times are appropriate, fumigants should be effective against all stages of insect development, from the egg to the adult. Fumigation does not however, provide any long-term protection. Treated artefacts must be well aired before they are removed from the fumigation chamber. The duration of airing will depend on the type of fumigant used.

Common fumigants include:

Dichlorvos (DDVP, Dichlorfos, Vapona)

• is the active ingredient in resin pest strips;
• is useful in storage environments and against general household pests;
• lacks penetration and is ineffective against insect eggs;
• reacts with alkaline materials;
• has been found to discolour some textiles, is corrosive to mild steel and black iron and can tarnish copper, silver and brass. It deposits a film on zinc, tin and lead;
• may damage artefacts if they come into contact with them;
• should be handled carefully as it is toxic to humans (acute oral LD₅₀ of 56-80mg/kg for rats) and is absorbed easily through the skin; and
• is not recommended for use in museum collections.

Ethylene Oxide

• has been widely used in the past, but its use is no longer recommended for the treatment of museum objects;
• is effective against major infestations, but is problematic due to its long retention by some materials and its reactions with some material types; and
• is a carcinogen and known to cause mutations.

Methyl Bromide

• is used to fumigate stored materials and soils;
• reacts with materials which contain sulphur;
• should not be used with woollens, viscose, rayons, vinyl, paper (sulphide process), rubber, furs, horse hair, feathers, leather goods and photographic chemicals;
• has no effect on oil paintings on canvas but some powdered pigments are affected;
• is very toxic to humans and is a potential carcinogen; and
• should only be used if there is a major infestation and if there are no other methods available.

Naphthalene (Mothballs, White Tar)

• is used as a fumigant and a repellent for general and domestic purposes;
• is only effective if used in well-sealed containers with exposure times of two to six weeks at ambient conditions;
• is considered non-corrosive and non-staining but has discoloured wool and may dissolve fats in biological specimens;
• should not come into direct contact with artefacts because it may damage them; and
• is a risk to the health of users as it is a skin irritant and inhalation of vapour is known to cause nausea, headaches and acute haemolytic anaemia.

Paradichlorobenzene

• is used as a fumigant and repellent for general and domestic purposes;
• is more volatile than naphthalene and is generally more effective - two weeks at room conditions is sufficient to kill the common clothes moth;
• can affect zinc white, lithopone, scarlet pigments, some cellulose acetate dyes, polystyrene foams, styrene and cellulose nitrate plastics, paper and ink; and
• is a health risk to users via inhalation, ingestion or eye and skin contact. Signs and symptoms of poisoning include vomiting, headaches, liver cirrhosis and kidney damage.

Organochlorine Insecticides

Insecticides in this group include aldrin, chlordane, dieldrin, lindane and pentachlorophenol. Due to their damaging effects on artefacts and health considerations they should not be used on museum artefacts or in buildings which contain collections.

Organophosphorous Insecticides

These compounds are generally more toxic than the organochlorine group but are usually applied at much lower concentrations, reducing the health risks slightly.

Chlorpyrifos

• is used as a contact insecticide and may be applied in a variety of forms (solution, granules, spray);
• has a residual action of about thirty days indoors but has poor knockdown and flushing capabilities. It can persist on wood for several years and has a longer residual action on non-porous materials than most insecticides;
• may affect nearby artefacts if they are not covered during its application;
• is corrosive to copper and brass and produces colour changes in some red dyes (acid red and disperse dyes); and
• is moderately toxic to humans via skin absorption, inhalation of dusts and ingestion. Symptoms may be mild (nausea and dizziness) or severe in extreme cases (fever, coma and respiratory failure).

Diazinon

• is used as a contact insecticide and is available in a variety of forms;
• has a residual activity of about 30 days indoors with a longer life on porous surfaces;
• is moderately to very toxic to fish, birds and bees;
• causes slight to very slight colour changes in acid red and disperse red dyes;
• may affect uncovered artefacts near the application site; and
• is a health risk to users in a similar fashion to that described for chlorpyrifos.

Malathion

• is a contact insecticide formulated as a wettable powder, a dust or an emulsifiable concentrate;
• is corrosive to iron, steel, tin plate and copper and produces unacceptable colour changes in acid red and disperse red dyes. As malathion’s effects on other materials are unknown caution is advised in its use; and
• is considered to be the least toxic of the organophosphorous insecticides but is highly toxic if ingested and may cause foetal abnormalities. Care must be taken when using it.

Carbamates

These materials are less volatile than organophosphates and consequently pose less of a risk of vapour poisoning.

Bendiocarb (Ficam)

• is a contact insecticide formulated as a dust or wettable powder. It has no fumigant properties;
• has a residual activity for weeks or months, depending on the environmental conditions;
• has no effects on acid red, telon red or disperse red dyes as it is applied as a powder; and
• poses some risk to health via inhalation, skin or eye contact or ingestion, though this is less so than with materials which possess higher vapour pressures.

Carbaryl (Sevin)

• is a contact insecticide available in a variety of formulations;
• has a moderate residual action depending on conditions (three to four days to several months);
• is non-corrosive but solvent effects may occur if it is allowed to contact artefacts;
• should not be allowed to come into contact with artefacts due to its residual activity; and
• is moderately toxic to people via inhalation, skin or eye contact or ingestion, toxic to bees, is a carcinogen (in rats), has caused genetic mutations in experiments and foetal abnormalities in many animals.

Propoxur (Baygon)

• is an emulsifiable concentrate which is also available as a pressurised spray and solution;
• has a good flushing action, rapid knockdown and a residual activity indoors of up to forty-five days;
• appears to have little effect on materials, though excessive wetting of plastics, rubber, asphalt and floor coverings should be avoided. Do not use on any materials prone to staining (carpets, curtains, wallpaper and the like). Avoid direct contact with artefacts; and
• is moderately toxic to humans via inhalation, skin or eye contact or skin absorption. It is also toxic to birds, fish and other wildlife.

Botanicals

Botanical insecticides are those derived from plants. The pyrethrin class is the most significant of the botanical insecticides. Commercially available synthetic pyrethrins (pyrethroids) have a greater residual activity and higher toxicity than their naturally occurring counterparts.

Pyrethrins

• act as contact insecticides and are available as pressurised sprays, dusts and oil solutions;
• are unstable and breakdown quickly to produce non-toxic residues;
• have rapid knockdown and flushing capabilities but do not always kill all of the insects knocked down;
• are often combined with other chemicals to increase their effectiveness;
• should not be allowed to come into direct contact with artefacts; and
• are of little danger to mammals but are toxic to fish.

Inorganics

Boric Acid

• is a stomach poison that is effective against crawling insects. It is relatively slow acting, taking from two to ten days to kill;
• can remain active for up to twelve months if applied in clean, dry areas;
• should not be applied directly to artefacts or be placed in areas where it will be contacted as no specific information is available regarding its reactivity with materials;
• should be handled carefully despite the relatively low risk of poisoning associated with its use; and
• has been used extensively in natural history collections as a substitute for arsenic.

Diatomaceous Earth

• is a desiccant insecticide often used in combination with pyrethrins;
• should not be allowed to come into direct contact with artefacts or be placed in areas where it is likely to be contacted as there is no specific information available regarding its reactivity;
• extends the persistence of pyrethrins when these compounds are combined; and
• can be forced into cracks and crevices where liquids would not be effective.

Bibliography

Dawson, J. E. (revised by T. J. K. Strang), 1992, Solving museum insect problems: Chemical control, Technical Bulletin No. 15, Canadian Conservation Institute, Otttawa, pp. 1-26.