The collections at National Museums Scotland encompass a wide range of object media, a large proportion of which can be susceptible to damage through pest infestation to varying degrees. The Preventive Conservation team has implemented an Integrated Pest Management (IPM) strategy over the past few decades, which has given us the tools to identify, prevent and treat issues relating to pests when they arise and has provided us a variety of methods by which to carry this out. One of the most recent additions to this strategy has been the use of parasitic wasps (Trichogramma) to deal with a long-standing issue with one of our collection items.
The Argyle 'Flying Fifteen' Motorcar
In one of the Main galleries at our Chambers Street Museum there is on open display, an Argyle ‘Flying Fifteen’ motorcar, built in the early 20th century. This car’s seats contain horsehair, which was a fairly common practice for the period it was built in, and something we see quite often. The horsehair has not been removed, and to do so would be incredibly difficult, as a result we have for many years had a concentrated colony of webbing clothes moths living inside the car, year on year. Many attempts have been made to reduce the number of moths in the car, such as removing sections of the seating for freezing, consecutive cleans and even a discussion of freezing the entire vehicle at one stage. Not only has this colony of moths caused damage to the car itself, with the larvae eating though sections of thread in the seats, but this also presents a risk to objects displayed nearby.
The Argyle 'Flying Fifteen' Motorcar
Damage caused by webbing clothes moth larvae to the seating of the Argyle ‘Flying Fifteen’ motorcar
Exploring Parasitic Wasps as a Solution
After hearing of parasitic wasps being used at a National Trust property in England as well as other case studies in Europe, it was deemed that trialling the wasps in a targeted approach may be a viable treatment. The type of parasitic wasps used in this trial are ‘Trichogramma evanescens’ and these can be used to disrupt the moth life cycle by parasitising the moths’ eggs. The wasps can be a welcome biological alternative to chemical treatments which can often have detrimental effects to both museum objects and staff members alike. The wasps are provided in sachets, which in our case contained around 6000 individuals which are then released slowly over the course of 3-4 weeks. The sachets should then be replaced to ensure a consistent population of wasps prevents the moth lifecycle from restarting.
Trichogramma Evanescens, at type of parasitic wasp
Monitoring Progress
The moth population inside the car is monitored using two pheromone traps, one in the front seat and one in the back. After the first year of deployment, a reduction in the number of moths caught on pheromone traps was observed at nearly every quarterly trap check. In 2024, numbers remained consistently low throughout the year, and while we can’t completely rule out climate related factors, this is a result we can now possibly link to this ongoing treatment.
Graph monitoring webbing clothes moth levels in the Argyle Motorcar over time
Due to the relatively localised nature of this infestation, the use of parasitic wasps has been ideal in this instance, and while they are limited to their effective range, this trial has provided food for thought as to other possible treatment areas. Our Chambers St Museum is a mix of modern and historic building, with many cavities and dead spaces which provide an ideal home to several of our recurring pest populations, and we are currently considering the use of parasitic wasps in these areas. In conclusion, I believe the continued use of parasitic wasps as a treatment method for controlling moth populations has been a success in this case, and I look forward to considering other applications for their use.