Using the Thermo lignum heat
process for treatment of
natural history specimens
Research and practical experience
David Pinniger
Integrated pest management is
essential to prevent insect damage to
collections
Main components of IPM

Checking for pests

Good housekeping



Good environment without extremes of
temperature or humidity
Quarantine procedures to prevent
introduction of live pests
Safe and effective control treatments for
objects
Options for control treatments

Low temperature

Anoxia

Carbon dioxide

High temperature
Low temperature



-20°C for 2
weeks
-3o°C for 3-5
days
Effective but
objects MUST
be bagged to
prevent
moisture
changes
Carbon dioxide


Effective, but
exposure can
take 3 weeks or
more
Issues with
registration in
some countries
Anoxia



Can be effective,
but exposure can
take 3 – 5 weeks
Difficult to
maintain 0.3%
oxygen for a long
period
Not effective for
some wood
borers
Heat treatment
Historical use of heat to kill insects



Heating food on sheets in
tropics
Heating buildings to kill food
pests
Heating insect drawers to kill
carpet beetles
How high a temperature do you need
to kill insects?
 52°C for most museum pests
 55° C g for some woodborers such
as Hylotrupes
1 to 2 hours exposure will kill
insect eggs, larvae, pupae and adults
The main issues using heat with
uncontrolled humidity


Drying out of objects
Splitting, shrinkage and cracking
What happens if you control the
humidity to a set level?


There is no
transfer of
moisture from
the object to the
environment
No shrinkage,
cracking or
distortion
Development of the ThermoLignum
Chamber



Computer controlled heat/ chamber
with RH control developed in
Germany
UK chamber in operation since 1994
Chambers also in Austria, Norway
Switzerland and Belgium
Operating system


The key is to introduce moisture in the heating
cycle
Remove moisture in the cooling cycle
Practical treatments
Objects treated for major UK museums
include:






Books
Archives
Textiles
Leather
Upholstery
Wooden objects
Contemporary Art
Trials at the Natural History Museum
London








Mammals
Birds
Crustacea
Insects
Vascular plants
Bryophytes
Lichens
Fish
Further trials to measure relative
humidity inside insect drawers
 Generally very stable and consistent
conditions in closed insect drawers
 Key issues
Spacing of drawers
to ensure sufficient
air circulation space
[See Ackery et al 2005 for details]
What is the effect of heat treatment on
DNA?


Some concerns that 52°C may affect
subsequent
DNA
extraction
from
specimens
Trials of fresh and aged insect material at
the NHM London showed no effect on
DNA extraction
[See Ackery et al 2004 for details]
Other research
Kigawa et al 2003

Tested the effects of a range of treatments
on DNA of fungi and chicken meat
Heat, freezing and anoxic treatments had
no measurable effects on DNA
Practical treatments of natural
history collections in the UK
Scarborough, England
Practical treatments of natural
history collections in the UK
Kew Herbarium
Key benefits in practice



Speed of treatment - 24 hour cycle
No need to bag objects – particularly costly
with large scale freezing programmes
Energy consumption - Need for detailed
cost breakdown of -30C for 3-4 days and
+52C for a few hours
Heat treatments in the future?



Ensure that there is clear understanding
of the difference between heat treatments
with and without controlled humidity
Demonstrate the low risks to collections
from controlled humidity heat treatments
Wider acceptance in the light of
advantages of labour input and energy
budget