May 26, 2016 at 3:42 pm #910
If you find you have an infestation, you will need to determine the most effective course of action. Chemical treatments using insecticides and fumigants may not be the best option, and are increasingly being replaced with safer, more targeted actions. The application of chemicals is not only hazardous to the humans, native wildlife and pets, but also to the collection, possibly causing tarnishing and corrosion of metals, staining and chemical alteration of certain materials. In addition, when over used they may make the items unsafe to handle.
If a pest infestation is found, implement the following non-chemical methods first.
- Inspect and isolate all infested or suspect material.
- Dispose of all non-collection material. It is often cheaper and safer to purchase more storage, display or promotional material than to treat it, or risk it continuing to harbour pests.
- Bag and seal affected collection items to contain infestations until the situation is controlled. This helps prevent the infestation from spreading. Use polyethylene bags or well-sealed containers. Label these clearly. (Do not use cardboard boxes, cardboard boxes provide many small spaces for insects to make a home.)
- Inspect neighbouring collections. Objects that have been stored near the infestation could also be affected. If in doubt, treat them as if they are affected.
Thoroughly clean the area including the floor, skirting, walls and shelving, by vacuum cleaning, followed by a slightly damp wipe.
- Consider using blunder and/or pheromone traps to monitor for remaining pests.
Once all the affected items have been isolated and bagged and the area has been cleaned, you will need to determine the most effective means of treating the collection items. The treatment of choice will depend on the type of infestation and the object’s material.
Treatment by freezing
Exposure to very low temperatures has been found to be lethal to all stages of the life cycle (eggs, larvae, adults) of many insects. Freezing those collection materials that we know can tolerate these conditions has been proved to be an effective and inexpensive alternative to other potentially toxic methods.
A large variety of materials can be safely frozen in order to kill pests. The success of freezing to kill insects depends on the temperature, the insect, and the material being treated. The drawback of freezing however, is the possibility of damage to some types of objects. Any material, which may become brittle and crack when frozen, such as wax objects, rubber and plastics, should not be frozen. Other objects, which may be susceptible to damage, if exposed to low temperatures are paintings, photographs and objects with glass elements. The museum industry has reported safe and effective freezing of textiles, furs, leather, paper and wood.
Domestic chest freezers are suitable for treating infested material, although their limitation of course, is their size. These can operate at temperatures of around minus 18°C to minus 24°C. This range is effective against most pests. Alternative measures will need to be found for items that are too big to fit into available freezers.
The freezing process:
- Turn the freezer temperature control to the coldest setting (this is only available on certain models) and allow time for the temperature to drop.
- Seal the item to be frozen into a polyethylene bag. It is preferable to reduce the amount of air in the bag. A small vacuum cleaner can be used, otherwise just work most of the air out manually. The less air in the bag, the less risk of water damage, should condensation occur when the item is removed from the freezer.
- Place the item(s) into the freezer.
- The length of time required in the freezer will depend on the temperature, the size and density of the item, and how densely packed the freezer is. The thinner the object, the more quickly its core temperature is lowered. Unfolding thick textiles will reduce the freezing time required, as will minimising the amount of material in the freezer. As a general rule, one week at minus 20°C is the minimum time required. If in doubt, extend the freezing time.
- It is helpful to have an indication of the temperature inside the freezer. Low cost digital thermometers that have the sensor at the end of a lead are available form electronic stores.
- Once the cycle is complete, remove the item(s) from the freezer and allow them to acclimatise over a day or so. Wear gloves to protect your hands as the items can be quite cold. Do not remove from the polyethylene bag until the item has returned to room temperature.
- Remove the item from the bag, and brush/vacuum the item to remove insect frass, bodies and casings.
A key point to remember when freezing to kill insects is to drop the temperature as low as possible, as quickly as possible, for as long as possible.
Once the item has been brush vacuumed, you need to decide whether it is safe to reunite it with the rest of the collection, either in storage or on display. If you are confident that the area is clean and free of infestation, then it is safe to return the object.
If, however, your IPM monitoring program has identified that you have an ongoing incidence of pest infestation, despite implementing the building maintenance and cleaning programs referred to above, then the judicious application of a pesticide is probably required. A perimeter treatment (around skirtings, doors, windows) of either a spray or powder pyrethrin based product is probably the sensible choice. Collection objects should not have these product applied to them directly, as they will cause damage.
It may be a good idea to consult a licensed pest control operator. Be sure, however, they are aware of the special precautions required when dealing with heritage material, and that they are happy to discuss and respect your particular requirements. Before taking this step it may also be a good idea to consult a conservator, and to do some extra reading. Again, the websites referred to earlier in this topic are good starting points.
Once you have experienced an insect outbreak, it is an indication that increased vigilance is required. Ensure a regular inspection program is implemented.
What if freezing is not possible?
If you cannot access a freezer, or the item is too large or cannot tolerate freezing, then you will need to investigate alternative measures. These will depend on the type of infestation and the objects concerned. If, for instance, you have a borer infestation in large wooden items then commercial fumigation using methyl bromide may be your only option. Discuss your needs in detail with the operator, and assure yourself that they do understand your particular concerns.
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