ERADICATION OF INSECTS FROM WOOL TEXTILES
Barbara M. Reagan
1 Part I chemical, Environmental, And Irradiation Methods
Museum personnel, private collectors, and university faculty responsible for maintaining textile collections frequently are required to make decisions or are asked questions pertaining to insect control on wool textiles. Decision making in this area becomes increasingly difficult with the enactment or revisions of state and federal laws and with new developments in chemical pesticides and alternative methods of eradication. It is the intent of this paper to present an overview of chemical and nonchemical methods of pest control applicable to museum and home use. The discussion of chemical insecticides is not limited to those EPA-approved for museums, institutions, or public buildings because many questions concerning fabric pest control come from private collectors. Furthermore, some of the less toxic insecticides approved for home use may eventually be approved for use in museums and other public buildings.
The commercial products listed as insecticides are those now approved for general or restricted use by the Environmental Protection Agency (EPA). The status of specific insecticides should always be checked because lists of EPA-approved products quickly become obsolete. In addition, many states have specific pesticide registration requirements, which often limit the geographic availability of commercial products. One may contact state agricultural extension specialists for information on state laws and requirements regulating the use of pesticides.
In addition to common methods of controlling insect growth on wool textiles, several unusual and alternative chemical, biological, and nonchemical methods of pest control are discussed below. These may serve as an inspiration for future research. Even though this paper focuses on elimination methods for controlling fabric pests, preventive measures (i.e., good housekeeping practices and periodic inspection of wool, feathers, furs, etc.) can reduce the risk of introducing insect populations into dwellings and storage areas or providing conditions that favor insect development.1
1.2 INSECT DAMAGE ON TEXTILES
Insect damage to wool-containing textiles in the United States is estimated at $200 million annually.2 According to the National Pest Control Association,3 fabric pests are making a comeback because most residual insecticides formerly used in their control (i.e., dieldrin and DDT) have been banned. Fabric pests attack wool and other protein-containing items such as feathers, skins, hair, and insect and animal collections. Insect damage can appreciably reduce the value of garments, carpets, upholstered furniture, and priceless heirlooms. Museum personnel, conservators, and owners of private or public collections often are confronted with the problem of controlling pests in textile storage areas or in individual items such as recent acquisitions that show signs of possible infestation.
The majority of insect damage to wool is attributed to the common or webbing clothes moth and the black carpet beetle; other insects and species of clothes moths and carpet beetles, however, also may cause considerable damage.4 Fabric pests commonly encountered in the United States include:5
- Webbing clothes moth, Tineola bisselliella Hum.
- Casemaking clothes moth, Tinea pellionella L.
- Carpet moth or tapestry moth, Trichophage tapetzella L.
- Plaster bag-worm, Tineola walshinghami Haworth
- Black carpet beetle, Attagenus megatoma F.
- Common carpet beetle, Anthrenus scrophulariae L
- Varied carpet beetle, Anthrenus verbasci L.
- Odd beetle, Thylodrias contractus Mot Schulsky
- Cabinet beetle, Trogoderma spp.
- Hide beetle, Dermestes spp.
In an excellent publication on pest control in museums, Kingsolver6 presents an informative and well-illustrated guide to these and other insect pests found in museums. By referring to this guide, one can greatly expedite the identification of common fabric pests—the first step in any eradication procedure.
Factors to consider when selecting a suitable method to control fabric pests include:
- the type of pest and its life cycle;
- the type and form of the item to be treated and its location;
- the potency of the treatment and the desired residual effect;
- toxicity and hazards to the environment;
- availability and cost;
- detrimental effects to the textile, including its fiber properties, dyes, and finishes;
- application equipment and personnel required, such as a licensed pest control operator (PCO) for “restricted use” pesticides; and
- federal and state laws governing the use of the chemical pesticides.7, 8, 9 The relative safety of a selected insecticide always should be ascertained before it is used.
The type of insect and its developmental stage should be considered when selecting an appropriate insecticide or investigating new or alternative eradication methods. Adult insects and young larvae, for example, are often more susceptible to insecticides than are eggs, mature larvae, and pupae. Similarly, clothes moths are more susceptible than carpet beetles to cedar vapors, temperature extremes, and certain insecticides.10, 11 Many insecticides that rapidly kill clothes moth larvae have little or no effect on carpet beetles.12 Higher concentrations of chemicals are usually required to protect wool textiles from black carpet beetles than from clothes moths.13 Furthermore, certain insect species reportedly build up tolerances to insecticides used to control fabric pests.
1.3 CHEMICAL METHODS OF CONTROLLING INSECTS
Pesticides are chemicals that kill or control pests. They are classified according to their function. Insecticides, for example, are chemicals used to kill insects, whereas herbicides are used to kill weeds.14 Pesticides are sold in a variety of usable forms, depending on the active ingredients and intended use. Some of the common forms of available insecticides for controlling fabric pests include fumigants, repellents, sprays, dusts, aerosols, fogging concentrates, impregnates (mothproofing agents), and attractants.15 These terms often reflect the mechanism by which the insect is controlled. Additionally, fabric pests can be controlled with chemicals that modify the chemical makeup of wool, function as antimetabolites, or control insect behavior; or they may be controlled biologically. In the following discussion, the various insecticides used to control clothes moths, carpet beetles, and other insects that attack textiles are discussed in terms of the control method.
Ware16 and Parker17 outline the various physical forms of pesticides available commercially. Sprays, for example, are available as emulsible concentrates, wettable powders, water-soluble powders, oil solutions, soluble pellets, or sprayable suspensions. It is beyond the scope of this article to discuss each form.
Most insecticides for fabric pest control are contact sprays which contain the active insecticide plus inactive aromatic hydrocarbons and petroleum-derivate solvents. Pesticide users should be aware of the insecticides as well as other additives in the formulation. A recent technical report from the Carpet Manufacturers Association18 stated that commercial insecticide products containing malathion, diazinon, or dichlorvos can cause color change and fading of some dyestuffs. Of particular interest to museum personnel are the results of the Survey of Pest Control Procedures (copies of which were sent to 300 museums).19 Several insecticides (e.g. p-dichlorobenzene, pyrethrins, and dichlorvos) which can cause specimen discoloration and deterioration were reported. In some instances, however, I question whether the degrading effects were due to the insecticide or to the solvents and additives in the commercial formulation. Thus, when evaluating the potential risk of insecticides on textiles, one should consider both the active insecticidal chemicals and the inactive dispersants, solvents, and other additives.
The use of pesticide chemicals in the United States is regulated by state and federal laws. The history of pesticide legislation has been reviewed by Dewey20 and Russell.21 Today the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA) as amended in 1972, 1975, and 1978, and as administered by the Environmental Protection Agency (EPA), is used to control the use of pesticides so as to protect the applicator, consumer of treated products, and environment.
All pesticide products must be registered with the EPA, must be classified for “general use” or “restricted use,” and must conform to specific federal labeling requirements. Pesticides registered for “restricted use” are those that may so adversely affect the environment that they can be applied only by a certified pest control operator. If a pesticide has been registered for “restricted use,” that should be clearly stated on the label.22
Even though a pesticide may be registered for “general use,” as is the case with “restricted use” pesticides, it may be used only at specific sites designated on the label and approved by the EPA. Thus, many pesticides suitable for home use cannot be used in museums, institutions, or public buildings. According to Stanley and McCann,23 very few insecticides are registered and recommended for use in museums (two are naphthalene and Dowfume 75—in fumigation chambers only).
Pesticide product labels also are required to contain “signal words” in bold print. These are extremely important because they represent the category of toxicity:24
Most insecticides are toxic to humans and should be used with great caution to avoid long-term health related problems. Insecticides usually are more toxic than other types of pesticides, such as herbicides and fungicides. Among the various chemical classes of insecticides, the organophosphates, carbamates, and organochlorines are the most toxic. The pesticide formulation also influences its toxicity; for example, liquid pesticides usually are more toxic than are granular forms because they are formulated in higher concentrations.
The relative toxicity of pesticide chemicals are described in terms of various hazard indicators, such as skin and eye effects, as well as in terms of Acute Dermal LD50, Acute Oral LD50, and Inhalation LC50 values, which are the lethal dosages (LD) or lethal concentrations (LC) necessary to kill 50% of the test subjects (for example, rats or rabbits for measuring toxicity to mammals).25, 26 In general, low LD50 values indicate high mammalian toxicity, whereas high LD50 values reflect negligible toxicity.
Pesticide applicators and users also should be aware of permissible safe concentrations of pesticide chemicals in the air to which humans can be exposed. These safe concentration limits, expressed as Threshold Limit Value (TLV), represent the concentration of the pesticide believed to be harmless to workers when they are continuously exposed for an 8-hour working day, 5 days a week. TLVs for specific pesticides also are reported for short-terms exposure (i.e., maximum allowable concentration for 15 minutes).27
Fumigants are usually highly toxic gases and liquids that are restricted to use only by certified applicators or by persons under their direct supervision.28 It's expensive to use fumigation techniques because special equipment is required, such as fumigation chambers, and users must be specially trained.
In general, chemicals used for fumigation are small, volatile molecules, many of which contain one or more halogens (Cl, Br, or F). Common fumigants that may be used to kill insects on textiles are listed in Table I.
TABLE I Insecticidal Fumigants
Fumigants usually kill all stages of the insect, but they do not protect against reinfestation. However, fumigating buildings and warehouses to eradicate populations of clothes moths, carpet beetles, and other fabric pests is rather uncommon, except when infestation is severe. In addition, favorable conditions usually are required for fumigation to be effective against certain insects such as carpet beetles.29
Care must be exercised in using fumigants because of their extreme toxicity and because of fire or explosive hazards, as indicated in Table I. Fumigants also may be damaging to textiles and cause metal surfaces to corrode.
Insect repellents are used to discourage insect attack, but many also effectively kill certain stages of specific insects. Some repellents, however, have no lethal effects on insects.
Two of the most common repellents used to control clothes moths and carpet beetles are naphthalene and p-dichlorobenzene, which, if used in high concentrations (i.e., 1 lb/100 cu ft), release vapors that may effectively kill clothes moth eggs and young larvae; however, they have little or no effect on eggs introduced into an area after they have been laid.30, 31 Naphthalene and p-dichlorobenzene also are classified as fumigants, so I have listed them in Table I.
1.3.4 Contact Sprays
Chemicals used as contact sprays and mothproofing agents kill by contact or by being ingested. They vary in effectiveness, mode of action, toxicity, residual properties, and form and method of application.32 The main chemical classes of insecticides used in contact sprays are: 1) organochlorines, 2) organophosphates, 3) botanicals, 4) pyrethroids, 5) dicarboximides, 6) thiocyanates, and 7) carbamates. The active insecticide (within each class) used for fabric pest control are given in Table II; also given are a few examples of commercial products containing the specific insecticide to illustrate the availability of the chemical in commercial formulations.
TABLE II Fogging Agents, Contact Sprays, and Mothproofing Agents EPA-approved for Fabric Pest Control
In general, the organophosphates, organochlorines, pyrethroids, and carbamates are residual-type insecticides with long-lasting effects.33 Throughout history, however, some of the most widely used insecticides have been obtained from the flowers, leaves, and roots of plants (the botanicals). Because many of them are less toxic than other chemical classes, they have been well suited for home use. The botanicals are usually fast acting, but they have little or no residual effect. Synergists such as piperonyl butoxide are frequently added to increase the toxicity of the botanical insecticides.
The toxicity values for the active ingredients in the contact sprays, fogging agents, and mothproofing agents are given in Table III. Usually lesser amounts of the more toxic insecticides, such as the organochlorines, are required for insect control. The merits of using larger quantities of the less toxic insecticides for a desired level of protection can be debated. Whether the contact sprays and mothproofing agents can be absorbed through the skin when individuals come into contact with the treated textile or item is questionable.34
TABLE III Toxicity Values for Insecticides Used to Control Fabric Pests.
1.3.5 Mothproofing Agents
Mothproofing agents have a greater residual effect than do most contact sprays, repellents, and fumigants. A few commercially available mothproofing sprays are sold for home use; however, many of the more durable formulations are applied industrially to wool textiles during processing or during dry cleaning. Mothproofing chemicals do not repell insects, but rather function as a stomach poison after the insect has ingested a small portion of the treated material.35
Some of the earliest mothproofing agents were compounds containing fluorine such as ammonium fluosilicate and zinc fluosilicate.36 These substances were dried into the wool textile. The products most commonly used as mothproofing agents in the United States are Mitin FF and Edolan U, which usually are applied to wool from acidified dyebaths at the boil for the greatest effectiveness.37 They bond to wool ionically by means of the sulphonic acid groups on the insecticide, similar to acid dyes. DDT and dieldrin, also organochlorines, were among the most permanent mothproofers available, but they can no longer be used legally because of EPA restrictions.38
Several commercially available mothproofing agents for home use contain methoxychlor, dichlorvos, or one or more of the pyrethroids (i.e., permethrin, resmethrin, and tetramethrin), as shown in Table II. As indicated by recent studies, permethrin has potential as a possible mothproofing compound for industrial application during dyeing.39, 40 Synthetic pyrethroids are similar to naturally occurring pyrethrins; they exhibit low mammalian toxicity and are biodegradable. Permethrin shows great promise as a mothproofing agent because it is photo-stable and is among the most insecticidally active pyrethroids available.41
The effectiveness of residual insecticides and mothproofing agents may be reduced by washing, dry cleaning, and exposure to light. Even so, wool textiles should be periodically cleaned, if possible, because contamination from perspiration, urine, food stains, air-borne organisms, and soil from handling can encourage insect growth. Clean wool lacks those substances, which commonly contain B vitamins, essential for insect development.42 Whenever possible, textiles should be cleaned before treating; otherwise, in addition to providing nutrients for insect growth, the dust and dirt may absorb some of the mothproofing solutions.
Certified pest control operators and professional exterminators also may apply contact sprays and mothproofing chemicals, usually by spraying the surfaces of the material to be protected (i.e., carpets, rugs, and upholstered furniture). (They commonly refrain from treating clothing items, however.) The mothproofing agents applied by these professionals are usually sprays prepared from oil or water solutions. Water-based solutions are suitable for rooms with poor ventilation and items having rubber or adhesive backings that may be damaged by oil-based sprays. Water-based solutions, on the other hand, may cause shrinkage, color loss, and staining on certain textile items.43
Antimetabolites are similar to known metabolites (i.e., vitamins, hormones, amino acids), but are not metabolized in the same way, so they disrupt the metabolic cycle and cause insects to starve. Other types of antimetabolites, like sulphonamides, may be used on wool textiles to inhibit the development of microorganisms, which supply important nutrients for insect growth.44
1.3.7 Chemicals that Control Insect Behavior
An alternative method for controlling insects on textiles and a possible area for future research is the use of chemicals that control insect behavior by impeding their ability to locate food, mate, or find suitable egg-laying sites. Another method with possibilities is the use of chemical attractants to lead insects into traps containing poisons or sterilants. Unlike insecticides, many of the chemicals used to control insect behavior are neither toxic nor polluting.45
1.4 BIOLOGICAL CONTROL
Certain types of microbial pathogens such as fungi, bacteria, and viruses can be devastating to insect populations. When they are used deliberately to control insects, the method is referred to as biological control. Microbial pathogens usually have a restricted host range and are harmless to higher animals and man. They have been used to a limited extent to control insects other than those that commonly attack wool textiles. Some of the advantages and disadvantages of biological control are discussed in Wool Science Review,46 but again, little research has been done on using this method to control insect growth on textiles.
1.5 CHEMICAL MODIFICATION OF WOOL
Another approach to reducing or eliminating insect attack on wool is by chemically modifying the wool protein, keratin. Methods explored include: 1) chemically modifying the cystine linkage or keratin's side chains, which would inhibit enzyme attack and protein digestion by the insect; and 2) chemically bonding toxic groups to the polymer chains.47 Although promising, none of these methods have achieved industrial significance.
1.6 LAUNDERING AND DRY CLEANING SOLUTIONS
Two of the simplest methods to kill the various stages of clothes moths and carpet beetles are washing the wool items in a strong solution of neutral soap or dry cleaning in a suitable solvent.48 Of course, neither method prevents reinfestation, although the cleaned article may be less attractive or nutritive and thus will inhibit insect growth. However, the cleaning solution may damage delicate or fragile historic textiles.
1.7 NONCHEMICAL METHODS OF INSECT CONTROL
Clothes moths and carpet beetles can be killed by extremes in temperature. Success depends on the exposure temperature and its duration. Rawle49 reported that all stages of the webbing clothes moths were killed by heating the infested area or item to 41° for 4 hours. The exposure can be shortened if higher temperatures are used. Exposure times are reduced to 11 minutes for clothes moths and 30 minutes for carpet beetles when the temperature is raised to 49°C. Textile pests also can be killed by immersing the infested item in hot water at 60°C.
Cold storage of woolens and furs is based on the premise that insect larvae are inactive at temperatures below 10°C. Before wool items and furs are placed in cold storage, they usually are disinfested in a suitable fumigation chamber.50 Kew51 reported that exposure at − 18°C for 48 hours effectively kills pupae, larvae, and adult cigarette beetles. Other researchers have shown that freezing is an effective means of killing both clothes moths and carpet beetles.52
1.7.2 Irradiation Disinfestation
The insect-killing power of electromagnetic radiation as an alternative to chemical methods has been investigated as a way to control pests in a variety of commodities, such as cereal products, wheat, flour, feed bags, and wood, to reduce insect damage during storage and transportation.53, 54, 55, 56 One of the first attempts to use electromagnetic radiation for insect control occurred more than 50 years ago when X-rays were used to kill beetles in packaged cigarettes.57 In several excellent review papers, Nelson58, 59 discusses the use, past accomplishments, current studies, advantages, and future possibilities for insect control with electromagnetic, sonic, and ultrasonic energy.
The use of gamma radiation, microwaves, and radiowaves for insect control has received considerable attention because of their advantages over chemical insecticides. Irradiation disinfestation is usually much faster than conventional chemical methods of insect control, it leaves no harmful residues, and it is easily adapted to continuous-process treatments. In addition, insects are not likely to develop a resistance to electromagnetic radiation treatments.60, 61
Reagan, Chio-Cheng, and Streit62 demonstrated that 2450 MHz microwave radiation will disinfest wool textiles without significantly changing the color of various acid dyes and natural dyes commonly used on wool or without causing a significant loss in fabric strength.
Most of the research on microwave insect control has been directed toward insects other than fabric pests. Because insecticides may have a detrimental effect on the dyes, finishes, and fibers in historic textiles, more research is needed on nonchemical methods of controlling insects on textiles. As stated by Edwards, Bell, and King:63
The discovery of efficacious nonchemical methods of pest control that are economically feasible for the average museum would be the best of all possible answers.
Commonly used chemical and nonchemical methods of controlling fabric pests on wool textiles as well as alternative methods that merit consideration and possible research have been presented. Careful attention must be given to the method(s) used in museums for disinfestation, especially when treating textiles that are in a fragile or damaged state. Preventive insect control procedures must be effective without damaging the textile. Research is continuing at Kansas State University to evaluate the effects of chemical insecticides on the physical and chemical properties of wool and the colorfastness of natural and synthetic dyes.