[Nhcoll-l] summary of response on dermestid and moth treatments

Thu Jun 19 15:08:01 EDT 2014

I wanted to provide a summary and update in response to my June 10 request for information about handling a dermestid and clothes moth infestation of vertebrate specimens.  Thanks so much to everyone for all the detailed and helpful responses!!!  We had a couple of folks from our entomology department come by to assess the situation and give us some advice as well.  Below is a summary of the practices we are implementing and a few alternative suggestions we received.  Sorry this got so long!  

Problem:  Found signs of dermestid (varied carpet beetle, Anthrenus verbasci ) and casemaking and webbing clothes moth infestation (Tinea pellionella and Tineola bisselliella) in some of our round skin and skull cabinets and on some mounts.  This is primarily a teaching collection, but more than half of the specimens have research value.  We wanted to avoid chemical pest control. 

Solutions:

TREATING SPECIMENS:

Although heating specimens used to be an accepted (and relatively fast) method of pest control, this degrades the DNA in the specimens too much to be used for specimens that have any research value.  This technique is NOT recommended. 

Freezing will kill all stages of most insects that are museum pests.  There were various recommendations about duration of freezing (2-3 days to 2-3 weeks at -20°C or colder), and using multiple freeze-thaw cycles to avoid insects entering diapause.  (Rapid cooling avoids this problem.) Given our lack of clean storage facilities and limited freezer space, a freeze-thaw cycle would be challenging.  Based on experiences of other museums knocking out infestations with only 2-3 days at -20°C and the recommendations of our entomology department that that would be sufficient to kill all stages of these pests, we are proceeding with freezing for 2-3 days.  We bag whole drawers full of specimens (Lane cabinet drawers just barely fit into a 42-gallon “contractor” garbage bag), duct-tape them to seal the bags, and place the drawers into the walk-in freezer.  Drawers are spaced on shelves to allow rapid freezing.  When we remove the drawers, we allow them to sit bagged for 24 hours to come to room temperature before we open the bags and return the drawers to a CLEAN cabinet.

You might find a neighboring museum with an anoxic cabinet that would allow you to bring specimens over for treatment.  This technique can take a month or more, depending on the pest.

TREATING WHOLE CABINETS:

To make sure that there are no lingering insects in the cabinets, our entomology folks recommended that we wash all surfaces down with warm, soapy water.  The manual pressure, the heat, and the soap would all help to kill or remove eggs.  They did not recommend stronger cleaners such as bleach.  Others recommended vacuuming with a HEPA filter vacuum cleaner.  We definitely wanted to remove any debris even if it was not living, so we could tell if we had a re-infestation. Because dermestid larvae seek out dark crevices, we were afraid there may be some lingering in holes or corners of the cabinets, even after a thorough cleaning. 

To treat the whole cabinet, we could have put it on a dolly, built a ramp, wheeled it into our walk-in freezer, and let it sit for 2-3 days.  Some suggested doing this with a cabinet full of specimens.  In this case, the challenge could be that you’d probably want to open the doors in order to ensure rapid cooling, but then you would likely have a condensation problem.

It would be possible to do the same thing with an empty cabinet in a walk-in drying oven.  Heating to 50°C for 4 hours is enough to kill all stages of these pests.

Our entomology colleagues suggested a solution for heat-treating empty cabinets in place.  (Given the cabinets are heavy and hard to move, and our freezer and drier space are limited and shared, this was a great solution for us.)  We just borrowed a space heater used under someone’s desk that could fit inside the cabinet.  We bought an oven thermometer (that had a low enough temperature range) with a wire probe so that we could monitor the inside temperature without opening the door.   Our seals were flexible enough that we could safely shut the doors over the cords, but if yours needed to stay slightly cracked to accommodate the cords, you could seal with duct tape.  (Make sure it is the real high-heat resistant duct tape, not a shiny look-alike.) We just needed to heat to about 48-50°C for 4 hours to ensure nothing was left alive in there.   Because we could not exactly regulate the temperature this way (it cycled up and down and occasionally approached 70°C), we were worried about damaging the cabinets or the seal.  I spoke with the always-very-helpful Nancy Zimmerman of Lane Cabinets and she said the elastomeric seals on their new cabinets were EPDM, which is very heat resistant.  Their production manager said heating to 70°C would be perfectly safe as that was well below what the seal and the paint could withstand.

Probably the safest way to treat an entire cabinet including its contents would be creating an anoxic environment, but this requires at least 2-3 weeks possibly 2-3 months to kill all stages of insects. “Did you ever try the static anoxia. In case of infestation and when our freezers are full,  we use the Escal film, RP system type K with Ageless Eye Oxygen.

 http://www.mgc-a.com/AGELESS/RPSystemFeatures.html
  We let on anoxia circa 2-3 months as soon as the Ageless Eye turn pink, we are great paranoiac people here. But the majority of conservators let it just for 15-21 days to one month.”

http://keepsafe.ca/oxygen-free-display-storage/ageless-and-rp-system-oxygen-absorbers/barrier-films/

IMPROVED PRACTICES AND MONITORING:

(1) Institute a regular policy of freezing all specimens that leave the cabinets before they are returned.

No problem with condensation: “We had a clothes moth problem several years ago, that we dealt with by freezing, and I don't envy you having to deal with your infestation.   To prevent another infestation, any specimen that leaves the collection area, whether for loan, exhibit etc. or any new specimen prepared, goes in our freezer before it goes back in the collection.    To deal with condensation, we don't bag specimens, but we have an empty cabinet in our collection that we place specimens after they come out of the freezer.    They usually stay there for few days and have never had a problem with condensation.    The humidity in our collection varies from 40-50% depending on the season, so I don't know if that helps.     The cabinet we use for this is an old one that isn't great for permanent storage but works for this.”

Bag to avoid condensation: “We routinely freeze material where we find any sign of dermestid damage. We also freeze all newly acquired material prior to inclusion into the collections. We use standard domestic chest freezers as we can’t afford anything else. We bag the drawers or posting boxes in heavy gauge plastic bags, seal them with tape and place them in the freezer for 1-2 weeks. The drawers are placed in the freezer with spacers between them to ensure rapid freezing. After the freezing period, the packets are placed on a bench or even left on a trolley until they come back to room temperature, overnight is even better. After this time the plastic bags are unsealed and drawers placed back into the cabinets. I would really urge you not to place the drawers straight back into the cabinets because then you will have condensation problems.”

(2) Line all cabinet drawers with white paper so any insect infestation can be detected more frequently. (Depending on what the drawers are made of, acid-free or acid-barrier paper can be used.) Monitor drawers weekly if you suspect an infestation, otherwise at least monthly.

“We found the moths attacked the side of the specimen that touched the drawer, whether the belly for mammals or back for birds.   I found if I didn't either lift the specimen or roll it over to check that side I missed some of the infected specimens.”

(3) On the inside of each cabinet door, post a sheet on which you can record each monitoring or treatment event. 

(4) Use traps and lures in cabinets and around room to monitor for insect activity.  Ensure they are checked on a regular schedule and lures replaced as needed. Dermestid beetles seem to be expert at avoiding sticky traps.  There is a food lure available for monitoring larvae but it will not trap them so they need to be checked every 2-7 days and then if empty moved to another cabinet.  (We are using these dermestid larva monitors http://www.insectslimited.com/store/museums-libraries-and-herbaria/dermestid-monitors-for-larvae.html )

Carola A. Haas
Professor, Wildlife Ecology
Dept. of Fish & Wildlife Conservation
112 Cheatham Hall
MC 0321 Virginia Tech
Blacksburg, VA 24061
cahaas at vt.edu
540-231-9269
http://www.fishwild.vt.edu/faculty/haas.htm

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