Disinfestazione di manufatti lignei da parassiti larvali mediante tecniche da vuoto
10.6092/issn.1973-9494/6179
I manufatti lignei sono soggetti ad essere fortemente danneggiati dall’attacco di parassiti che, nella loro forma adulta, prolificano nel legno depositando le loro uova. Tra le specie più pericolose ci sono gli insetti xilofagi, le cui larve sono responsabili di uno dei più efficaci meccanismi di degradazione dei manufatti artistici lignei. La loro eliminazione, da sempre, costituisce un problema enorme per lo stato di conservazione del legno. In questo lavoro, viene presentata la sperimentazione di una nuova semplice tecnica da vuoto per la disinfestazione del legno da parte del Hylotrupes bajulus nella sua forma larvale. Viene inoltre presentata la possibilità di trattare manufatti lignei di grandi dimensioni per mezzo di una speciale camera da vuoto.
application/pdf
1973-9494
6179
en
Amerigo Beneduci
Conservation Science in Cultural Heritage
worm dehydration
Woodworm Disinfestation of Wooden Artifacts by Vacuum Techniques
Text.Serial.Journal
https://conservation-science.unibo.it/
15
Articles
2015-12-30
2016-05-31
2015-12-30
2017-09-04
267-280
CSCH
Amerigo Beneduci
2015/12/30
10.6092/issn.1973-9494/6179
267
Università della Calabria, Cosenza
1973-9494
worm dehydration
en
280
Woodworm Disinfestation of Wooden Artifacts by Vacuum Techniques
https://conservation-science.unibo.it/article/download/6179/5953
15
W       OODWORM DISINFESTATION OF WOODEN ARTI-
        FACTS BY VACUUM TECHNIQUES

   Giuseppe Chidichimo*, Francesco Dalena, Amerigo Beneduci
   Dipartimento di Chimica e Tecnologie Chimiche
   Università della Calabria, Cosenza, Italy


  Keywords: wooden artifacts, hylotrupes bajolus, worm disinfestation, vacuum,
worm dehydration


   1. Introduction

   Any wood artifact is an ideal incubator for xylophagous insects. They can survive in
wood for many biological cycles, involving egg deposition, larval worm development
and finally, the transformation of the worms into insects. During the larval stage, the
worm uses the cellulose contained in the wood to nourish itself and as a consequence
bores deep tunnels through the wooden artifact, destroying the mechanical perfor-
mance of the material. This problem, in the large majority of conservative interven-
tions, is solved by exposing the artifact to chemicals which, in the case of accidental
spillage, can be dangerous for workers performing conservation operations. These
methodologies have the further inconvenience of not being very effective in destroying
the insects’ eggs.
   Methods used for woodworm disinfestations can be classified into two major cat-
egories: chemical and non-chemical. A detailed comparison of the most widely used




                                                                                                CONSERVATION SCIENCE IN CULTURAL HERITAGE
methods for controlling woodworm attacks can be found in the works of Lewis and
Haverty [1,2]. Chemical products that must be directly applied to the wood, include py-
rethrum aerosol and pyrethroid aerosols and liquids (cyluthrin, permethrin, bifenthrin)
liquid imidacloprid, liquid nitrogen, and liquid and powder formulations of disodium
octaborate tetrahydrate [3].
   All these substances have to be carefully handled by trained operators for the rea-
sons mentioned above. As a result, there is growing interest in non-chemical insect
control. Non-chemical treatments for wood disinfestation include heat (lethal levels
- above 53 ºC- for at least 33 minutes - are used on the wooden artifacts ensuring the
death of the parasites [2]; this method however, can damage the wooden artifacts),
electrocution (based on high voltage-low current devices) with effectiveness as low as
44% [2] and microwave (MW) irradiations [4].
   This paper describes a new technique of disinfestation based on the possibility of
producing irreversible damage to worms by creating vacuum conditions around the
artifact. The aim of this study therefore was to find a useful protocol for worm disin-
festation by vacuum and more precisely, to find the minimum vacuum treatment time
for complete disinfestation of walnut wood (Liquidambar styraciflua) from Hylotrupes
bajolus larvae.


* Corresponding author: giuseppe.chidichimo@unical.it


                                                                                          267
                                                                                                               To our knowledge, no experiments have been made regarding this argument. To-
                                                                                                            day, creating a vacuum around an artifact does not seem to be a complex matter and
                                                                                                            is an interesting way to ascertain the possibility of worm disinfestation as the method-
                                                                                                            ology avoids the use of harmful chemicals, physical heat or electromagnetic radiation
                                                                                                            treatment, which can produce wood dehydration.
G. Chidichimo, F. Dalena, A. Beneduci - Woodworm disinfestation of wooden artifacts by vacuum techniques




                                                                                                              2. Experimental part

                                                                                                              The apparatus used to perform the vacuum experiments is illustrated in Figure 1.
                                                                                                            This was essentially constituted by a spherical dessicator made in Plexiglas, thick
                                                                                                            enough to withstand a gradient pressure of more than 1.2 bar between the external
                                                                                                            and internal surfaces, connected to an Edwards rotary vacuum pump able to create a
                                                                                                            vacuum of 10-2 bar, and an appropriate pressure gauge.




                                                                                                                              Figure1. Apparatus used to perform vacuum experiments

                                                                                                               In order to perform a significant number of experiments it was necessary to breed
                                                                                                            Hylotrupes bajolus larvae by choosing as an incubator chestnut wood already infested
                                                                                                            with worms. Infested chestnut wood trunks (with an average diameter of 10 cm) were
                                                                                                            kept for 9 months at a temperature of 20°C with a relative humidity level of 70% in suit-
                                                                                                            able ventilated containers. These environmental parameters allowed optimal growth of
                                                                                                            a sufficient number of larvae to carry out our experiments. Figure 2 shows a Hylotrupes
                                                                                                            Bajolus larva.




                                                                                                                                        Figure 2. Hylotrupes Bajolus larva


                                                                                                      268
    Preliminary experiments were conducted on larvae extracted from their natural en-
vironment (i.e. the wood where they were bred) and placed in isolation in the apparatus
shown in Figure 1. They were then exposed to a vacuum of 10-2 bar. The experiment
showed that the larvae are able to maintain their viability for a few hours in these
vacuum conditions. Only after more than 10 hours treatment, the worms, in their larval
state, lost their mobility and appeared to be smaller in diameter. We therefore con-
cluded that under vacuum conditions, worms gradually lose water and become pro-
gressively dehydrated. Worms that were kept isolated moreover, were no longer able
to rehydrate themselves to regain their viability. At this stage we were unable to answer
the following question: did worms that were kept in their natural habitat and subjected
to vacuum conditions inside their tunnels behave in the same way as isolated worms,
or could they rehydrate themselves by retrieving water from the wood? In other words,
we were unsure whether the conclusion regarding the worms extracted from their natu-
ral environment could be assumed valid for the worms left in their habitat, as is the
case for larvae-infested artifacts, without any further evidence. Worms inside the wood
could indeed rehydrate themselves by taking moisture from the wood by mechanisms
of diffusion or simply feeding on the cellulose.
    Another problem to solve was to find measurable parameters which would indicate
worm death.
    Our conclusion was that in order to solve these problems, experiments would need
to be conducted leaving the larvae inside their natural habitat and measuring a number
of parameters linked to their activity to ascertain their viability. To this end, the larvae
contained in the pieces of chestnut wood where they had been naturally bred were
subjected to vacuum conditions. All chestnut wood testing samples were of a cylindri-
cal shape measuring 5 cm in height and with a diameter of about 10 cm. Each of them
contained a single worm nested in the area between the bark and the dead wood.
In order to follow the viability of the larvae in the course of the vacuum treatment we
opted to measure the quantity of waste powder produced by the worm during its eat-




                                                                                                     CONSERVATION SCIENCE IN CULTURAL HERITAGE
ing activity. This waste material can be easily collected by simply tapping the cortex
of the wood cylinder next to the open cavity created by the worm, placing the sample
with the cavity face down. A sample used in the experiments (sample N.7), as well as
the waste powder produced by the worm at certain stages of the experimentation is
shown in Figure 3.




                    Figure 3. One of the samples used in the experiments


                                                                                               269
                                                                                                               The cavity produced by the larva is clearly visible on the left side of the sample. The
                                                                                                            waste powder extracted by the procedure described above is also shown.
                                                                                                               Experiments were carried out on control samples, where larvae were left undis-
                                                                                                            turbed, and samples submitted to 8, 24, 120 and 140 hours of vacuum treatment at a
                                                                                                            pressure of 10-2 bar. For each of these conditions three samples were tested in order to
G. Chidichimo, F. Dalena, A. Beneduci - Woodworm disinfestation of wooden artifacts by vacuum techniques




                                                                                                            reduce experimental error. The waste powder was collected and weighed at given time
                                                                                                            intervals. Overall research time was 35 days for each sample. From now on, the waste
                                                                                                            powder produced by the worms will be referred to as WP for brevity.


                                                                                                               3. Results and discussion

                                                                                                               WP produced by the worms’ feeding activity during the vacuum experiments are
                                                                                                            reported in Figure 4. At the beginning of the experiments, each of the samples was
                                                                                                            cleaned by removing all the WP produced until then by the hosted worm. On each of
                                                                                                            the days corresponding to the experimental points reported in the graphs in Figure 4,
                                                                                                            the accumulated WP was removed from the samples, then weighed. The result corre-
                                                                                                            sponds to the WP produced in the interval between the actual and previous measure-
                                                                                                            ment of the day before. The weight of this WP was then added to the previous one.
                                                                                                            The vacuum treatment started on the 9th day of experimentation in all of the cases, as
                                                                                                            indicated by the black arrow in Figure 4.

                                                                                                                                                     4,0

                                                                                                                                                     3,5           8 h vacum
                                                                                                                                                                   24 h vacum
                                                                                                                                                                   120 vacum
                                                                                                                                                     3,0
                                                                                                                           Waste Powder Weight (g)




                                                                                                                                                                   144 vacum
                                                                                                                                                                   Control
                                                                                                                                                     2,5

                                                                                                                                                     2,0

                                                                                                                                                     1,5

                                                                                                                                                     1,0

                                                                                                                                                     0,5

                                                                                                                                                     0,0
                                                                                                                                                           0   3   6   9   12 15 18 21 24 27 30 33 36 39
                                                                                                                                                                                Time (days)

                                                                                                            Figure4. WP produced by the worms as a function of days, for four different vacuum times (hours)
                                                                                                            treatments and for the control sample that was not vacuum treated. Points corresponding to each
                                                                                                            of the trends represents the average WP quantities measured from the activity of three different
                                                                                                            worms (see text). The vacuum treatment started on the 9th day, indicated by the black arrow.

                                                                                                               First of all, it is interesting to note that the total amount of WP produced by the
                                                                                                            control worm samples follows an almost linear trend from the beginning to the end of
                                                                                                            the experiments. The slope is 0.10 grams/day with a margin of error of about 4%. This
                                                                                                            means that the eating rate of the control worms remains constant and is not affected
                                                                                                            by manipulation of the samples during the WP collecting procedure. In the other cases,
                                                                                                            before vacuum treatment, the slope of the WP accumulation remains very close to that


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of the control, while after treatment, the WP accumulation loses the linear trend to as-
sume an exponential one. This is clearly seen in Figure 4 where the linear fit for the
control and the exponential fit for the vacuum treated samples are reported as continu-
ous lines. The exponential fit is described using the following equation:
                                     WP = WP∞ + Ae–kt
where, WP is the cumulative waste powder produced at the time t, WP∞ is the cumu-
lative waste that would be produced at infinite time, k is the kinetic constant of worm
degradation expressed as days-1 and A is a pre-exponential factor which is related to
the starting WP accumulated at the time of vacuum treatment.
    The fitting results are reported in Table 1.

Table 1. Exponential Fitting results of the WP data of vacuum treated worms shown in Figure 4

    Sample                    WP∞                         k                      R2
       8h             3,17274 (0,43887)             0.06 (0.03)                0,94954
      24 h            2,98241 (0,39273)             0.07 (0.03)                0,92817
     120 h            2,09386 (0,05906)            0.106 (0.022)               0,98029
     144 h            2,13252 (0,01226)            0.125 (0.005)               0,99948
                   Values in parenthesis are standard deviations of the data

   It is interesting to note that the metabolic activity of the worms does not stop abrupt-
ly with the beginning of the vacuum treatment (Figure 4), but gradually decreases to
zero in an exponential trend. The kinetic constant of this trend gradually increases as
the vacuum time increases, as shown in Table 1. We can assume that this constant
represents the rate of worm degradation induced by the vacuum treatment. Therefore,




                                                                                                      CONSERVATION SCIENCE IN CULTURAL HERITAGE
the longer the treatment, the faster the degradation. This is also reflected in the rate
at which the WP reached infinite value. This was indeed reached after about 15 days
from treatment in the cases of the 120 h and 144 h samples (5 and 6 days of vacuum
treatment, respectively) while, only after about 25 days in the other cases (0.3 and 1
day of vacuum treatment).
   In addition to the waste production analysis, at the end of the experiment, we ob-
served each of the treated worms and found that all of the worms examined had died
as a result of the significant dehydration caused by the vacuum treatment.
   Summarizing the results, we have shown that for a vacuum time of the order of 8
hours, worms stop their activity completely after about 25 days post treatment. For
the longer vacuum time treatments of 120 and 144 hours (5 and 6 days) worm activity
stops after about 10 days from treatment. Moreover, visual inspection of the worms
at the end of the experiments, enabled us to verify that their death had been brought
about by dehydration induced by vacuum.
   Therefore, we can conclude that 8 hours of vacuum treatment at 10-2 bar are enough
to disinfest wood artifacts from Hylotrupes bajolus. Although worms will continue their
activity for some time after they have been exposed to the vacuum, the biological
damage caused to them during the treatment is irreversible and ultimately leads to the
worms’ death.
   This appears to be a very promising technique, since it does not expose operators
to any chemical or physical risk.


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                                                                                                              Acknowledgements
                                                                                                              The authors are grateful to the Italian Minister of University and Scientific Research
                                                                                                            (MIUR) for financial support under the project IT@CHA PON01_00625.
G. Chidichimo, F. Dalena, A. Beneduci - Woodworm disinfestation of wooden artifacts by vacuum techniques




                                                                                                                  References

                                                                                                            [1]     Lewis, V. R. (1997). “Alternative Control Strategies for Termites.” J. Agric. Ento-
                                                                                                                    mol. 14, pp.291-307.
                                                                                                            [2]     Lewis V. R., and Haverty M. I. (1996). “Evaluation of Six Techniques for Control of
                                                                                                                    the Western Drywood Termite (Isoptera: Kalotermitidae) in Structures.” J. Econ.
                                                                                                                    Entomol. 89(4), pp.922-934.
                                                                                                            [3]     Plaza P.J., Zona A.T., Sanchís R., Balbastre J.V., Martínez A., Muñoz E.M., Gor-
                                                                                                                    dillo J, and de los Reyes E. (2007). “Microwwave Disinfestation of Bulk Timber”.
                                                                                                                    Journal of Microwave Power & Electromagnetic Energy. Vol. 41, No. 3, pp.22-37.
                                                                                                            [4]     Chidichimo G., Dalena F., Rizza A, Beneduci A. Results (under review).


                                                                                                                  Biographical notes

                                                                                                               Giuseppe Chidichimo is full professor of physical chemistry at the University
                                                                                                            of Calabria (UNICAL), Italy. He has been head of the Department of Chemistry at
                                                                                                            UNICAL (1987-1996), President of the Scientific and Technological Park of Calabria
                                                                                                            (CALPARK) (1996-2000), President of the Course of Studies in Chemistry at UNICAL
                                                                                                            (1998-2003) and President of the Italian Chemical Society - “Calabria” section for two
                                                                                                            periods of three years. In 1997 he received the “Laurea Honoris Causa” at the Uni-
                                                                                                            versity of Niznj Novgorod (Russian Federation). He has founded three active Spin Off
                                                                                                            companies: TEBAID (for technology transfer in the field of innovative materials); DIAR-
                                                                                                            CO RESTAURO (for technology transfer in the field of Cultural Heritage Conservation
                                                                                                            and Restoration; SIRIA (for technology transfer in the field of environmental studies).
                                                                                                            He is author of more than 200 scientific papers and 20 international patents, concern-
                                                                                                            ing basic and applied research in the field of innovative materials, physical chemistry,
                                                                                                            Cutural Heritage conservation. He has been Invited Speaker at many national and
                                                                                                            international scientific meetings.

                                                                                                                Amerigo Beneduci, completed his MS (cum laude) in Chemistry at the University
                                                                                                            of Calabria (UNICAL), Italy, in 1998 and obtained his Ph.D. degree in Chemistry from
                                                                                                            UNICAL in 2002. From 2003 to 2008 he worked as research fellow at the Department
                                                                                                            of Chemistry-UNICAL. He also served as adjunct professor of analytical chemistry
                                                                                                            from 2003 to 2008 and as professor of thermodynamics and chemical kinetics from
                                                                                                            2012 to 2015. Dr. Beneduci is author of more than 30 peer-reviewed papers and has
                                                                                                            attended several international and national meetings as speaker. He is the co-founder
                                                                                                            of the Spin Off company SIRIA for which he is supervisor of the chemistry area.

                                                                                                                Francesco Dalena has an MS in Chemistry with a specialization in “Chemistry
                                                                                                            of advanced materials”, from the Chemistry Department of the University of Calabria
                                                                                                            (Italy). He is a Ph.D. student at UNICAL working on a project on the restoration of
                                                                                                            wooden artifacts and ancient papers infested by biological agents.


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