CONTROL

THE DEATH-WATCH – ACCOMMODATED IN ALL THE BEST PLACES

Steven Belmain from the Natural Resources Institute, Monique Simmonds from the Royal Botanic Gardens, Kew, and Brian Ridout from Ridout Associates in the UK report on the final frontier of Integrated Pest Management – our cathedrals and listed buildings

Introduction beetle laid its eggs on or close to the surface of the wood. Preservation of historical buildings is a hot topic, and g e t t i n g The hatched larvae then burrow into the timber and hotter if predictions about global warming and climate continue to feed on the wood until they have grown suffi- change impact upon the built environment in the way we ciently to pupate. The adult emerges during the spring, think they will. Invasions of exotic and extre m e mates and renews the cycle. It is now established that the life population fluctuations of indigenous species are widely cycle depends on the suitability of conditions, and that the re p o r ted around the world. Timber pests are no exception, larval stage may vary from one year in ideal conditions to and we have already seen termites establish themselves in 12 years or more, if conditions are not favourable. Death- Southwest England and observed an increase in the watch beetle larvae develop more rapidly when there is a p r evalence of the house longhorn beetle, H y l o t r upes bajulus. high relative humidity and the presence of fungal decay in This may be partly due to climate change, but it is also the timber. Whereas the short-lived adult does not directly p r obably related to changes in lifestyle. Central heating feed on timber, the larva causes considerable damage as it systems are now present in most historical buildings. And digests its way through the wood, creating structural and coupled with reduced ventilation, it can lead to condensation aesthetic damage to our buildings. New research has shown and warm e r, more humid environments inside buildings, that the adults do not necessarily need to emerge from the c r eating a more conducive environment for timber pests. timber and can mate in cavities within the timber. Further- It is also feared that another European timber pest, the more, newly mated adult females have been shown to re- death-watch beetle ( rufovillosum), is on the enter existing flight-holes and lay their eggs deep in the increase, which is a particular worry for architectural timber, rather than on or near the surface. These observa- conservationists as the beetle has a preference for ancient tions have highlighted why existing treatments are often timber found in cathedrals, palaces and stately homes ineffective. (Belmain et al., 1998). Historically, beginning with attempts to treat the roof timbers of Westminster Hall at the beginning Tapping of the 20th century, surface treatment with chemicals has The death-watch beetle has been living in our buildings for been employed as the treatment method of choice. Surf a c e centuries and was first noted for the tapping sound the adult t r eatment has proved, however, of very limited effect in controlling the death-watch beetle in such historic buildings. As a result, between 1993 and 1997 the European Commission funded the international collaborative research project Woodcare, led by English Heritage, to understand the interaction between beetle behaviour, timber and fungus with a view to understand why surface treatments so often fail, and to evolve alternative environmentally acceptable treatment methods (Ridout, 1999). This short article outlines the problems involved in the effective control of death-watch beetle and some of the research which has been carried out to discover why it is so problematical and to develop better methods of control.

Figure 1. The death-watch The death-watch beetle (Figure 1) beetle, Xestobium rufovil- losum, one of the primary Life cycle pests affecting hardwoods in For many years it had been thought that the life historical buildings across cycle of the death-watch beetle was a maximum Europe. Adult (left) and of 5–7 years (Fisher, 1940), and that the adult Larva (right).

DOI: 10.1 0 3 9 / b 0 0 9 2 7 0 n Outlook – December 2000 2 3 3 This journal is © The Royal Society of Chemistry 2000 PEST CONTROL makes. When people usually died at home in ancient structural oak used in historic buildings was converted and Europe, the death vigil, or death watch, would have allowed assembled green, when the moisture content was still very this tapping noise to be clearly audible when the house was high, and it is likely that some timbers used had already quiet, the noise emanating from the structure of the house. suffered minor fungal attack before felling. In larger section The tapping noise subsequently became associated with bad timbers, the moisture content would have remained high omens, implying that when the tapping noise was heard a enough to sustain fungal attack for many years, and so a loved one would soon die. We now know the tapping is a suitable environment for long term death-watch beetle in- form of communication employed for finding mates, festation was present in the building from the outset. Many through research conducted by Martin Birch and colleagues have argued that the death-watch beetle larvae, themselves, at Oxford University (Goulson et al., 1994; Birch and were introduced into the buildings within the timber used Keenlyside, 1991). for construction. Lack of maintenance over the ensuing years inevitably allowed periods of water ingress, setting up new fungal attacks, and consequent fresh food sources for Environmental conditions the infestation. Our Irish collaborators based at University In many cases of active infestation, the environmental College, Dublin have studied the chemistry of conditions allowing the beetle larvae to survive are only just expansa which has helped us understand the complex rela- met, so that the life cycle is continuing, but at a very slow tionship between the death-watch beetle, timber, and fungus. rate; and structural damage occurs at a proportionally slow Research has shown that the death-watch beetle uses rate. However, a relatively small change to the environment fungally-produced compounds to ‘home in’ on suitable areas can cause the attack to die out, or conversely, to become of timber for infestation. more active.

Moisture Chemical control At present it is thought that a moisture content of 14% is Since the advent of chemical , they have been the lower limit for a flourishing colony of death-watch increasingly used in timber pest control. Various nasty , and if the moisture content drops below 12%, the chemical concoctions were developed from the beginning of larvae will die. It, therefore, ought to be a simple matter of the 20th century and applied as blanket treatments ensuring that the moisture content is below this level, and whenever pest problems were identified in buildings. For the infestation would cease to be a problem. Unfortunately, example, a formulation developed by Harold Maxwell- even in a fairly well ventilated roof space, the normal Lefroy of Imperial College, London, consisting of 50% moisture content of structural timber averages 14–15%, and tetrachloroethane, 40% trichloroethylene, 6% cedarwood in many buildings in which this beetle is a problem (such as oil, 2% solvent soap and 2% paraffin wax, was used for the irregularly heated churches), condensation coupled with treatment of the roof timbers of Westminster Hall in central poor ventilation can significantly increase this moisture London in the 1920s. In many countries, lindane and level. As temperatures within buildings can wildly fluctuate dieldran continue to be used for timber treatment. However, between summer and winter, causing subsequent changes in toxicity concerns are resulting in their replacement with moisture content, it is likely that the beetle larvae can safer pyrethroid alternatives such as permethrin. tolerate periodic drops in moisture below their optimal requirements. In the long term, Figure 2. The nave of therefore, every effort should be concentrated on Salisbury Cathedral (left) ensuring that the environmental conditions are which has a relatively low population of death-watch adjusted, first to slow down, and ultimately to beetles thanks to building kill off, the beetle attack. The improved, drier works aimed at reducing environment must then be maintained year after damp and humidity in the year (Figure 2). Even if these improvements can building. The roof area be achieved, it may still be necessary, over the above the nave (right) was one of the trial sites used short term, to introduce chemical control where to test the efficacy of the beetle is particularly active. It is of course differently coloured sticky essential that moisture levels in surrounding traps for pest monitoring. masonry are measured and reduced as necessary. If this is not practicable, the timber should be isolated from the damp masonry as much as possible.

Fungal decay For the death-watch beetle to flourish, timber is usually required to have been previously modified by fungal decay (often by the oak rot fungus Donkioporia expansa), making the timber more easily digested. The vast majority of

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The situation of blanket chemical treatments has become larvae can take upwards of 10 years to complete their institutionalised through the property market and insurance development (Fisher, 1940), implying that surface treat- company requirements for timber treatment certificates. ments with pesticides would have to be either very long However, more recently, several forces have been at work lasting or repeatedly applied to the timber over a number of which call into question the use of pesticides, especially with years to have any impact upon pest populations. regard to the death-watch beetle. There is an increasingly widespread concern about the safety of pesticides, with consumers in many countries demanding reduced usage in agriculture and in urban envi- Monitoring ronments. This is affecting the alternatives available to the Better prospects for timber pest control are now becoming a timber preservation industry. More importantly, with the reality. Research within the Woodcare project has aimed at death-watch beetle there are many reported incidents of discovering potential solutions to control the death-watch poor efficacy of pesticide treatments, most notably in beetle and preserve cultural landmarks such as cathedrals Westminster Hall (see above). The Hall experienced massive and palaces from continuing damage. The first step in death-watch beetle damage after the Second World War designing an integrated approach to pest control is to ensure initiated by ingress of rain water through bomb holes in the that there are effective monitoring tools to detect pest roof, and despite repeated pesticide treatments over a populations. The most common and perhaps most obvious number of years, the Hall continued to have high infesta- method usually employed to identify actively infested timber tions for decades until the timbers slowly dried out. has been the presence of insect emergence holes. However, The death-watch beetle is particularly ill-suited for most timbers in historical buildings are riddled with insect control by pesticides for a number of reasons related to its holes, and distinguishing between currently active and hist- biology and habitat. Perhaps one of the most difficult orical infestation is difficult. Our research has shown that problems is related to pesticide application. The larvae of holes and the presence of frass or wood dust around the the death-watch beetle feed on hardwoods such as oak, holes do not necessarily indicate an active infestation and often deep within large timbers hewn from entire trees. that death-watch beetles can also emerge out of pre-existing Because of the size of the timbers and the inaccessibility of holes leaving no new tell-tale signs (Ridout, in press). the pest, even pesticide injected into affected timber under Monitoring for pest infestation can be more effectively done pressure often fails to reach its target. Other forms of using light traps (Figure 3) and sticky traps (Figure 4), which pesticide delivery such as fumigating fogs or liquid and paste we have found to give a good indication of active infestation treatments on the surface of the timber are even worse at (Belmain et al., 1999). Another new monitoring tool is being reaching larvae deep within it. Of course the adult death- developed by our collaborators in The Netherlands (TNO watch beetles must eventually emerge from the timber to Building and Construction Research) using ultrasonic mate and lay eggs. However, killing the adult is also no easy sensors. When these small sensors are placed on the surface task. Adults usually emerge simultaneously in the spring of the wood, they can detect the sounds the make within a fairly narrow window of time, and our research has when eating the wood, thereby pinpointing areas of a shown that their contact with the treated surface is limited building that are infested. This will allow the pest control by their behaviour in seeking out cracks and crevices and operator to focus pesticide applications on specific areas, their preferences for dark areas (Belmain et al., 2000). Poor increasing efficacy and cost-effectiveness, as well as to treatment success is further compounded by the fact that the monitor the success rate after treatment.

Figure 3. Research using UV insectocutors placed in roof spaces Figure 4. Coloured traps can be placed in relatively has found them to be effective tools in monitoring for the inaccessible roof spaces or other areas suspected of death- presence of timber pests. As the UV light is attractive to watch beetle infestation. Based on the number of insects insects, it may also be contributing towards pest population caught on the traps, appropriate remedial decisions can be reduction. made.

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Integrated control Effective monitoring and targeted application of pesticides is, however, only part of the new integrated approach being developed for timber pests.

Biological control Biological control, now widely used in agriculture, can also work in buildings. Predators of the death-watch beetle such as and a small blue beetle, caeruleus (Figure 5), are naturally found in buildings. The predatory beetle is particularly interesting because it seeks out its prey inside the timber providing a means of controlling pest larvae deep inside timbers where pesticides do not normally reach. Biological control alone is unlikely to rid our buildings of pests, but if pest managers promote conditions which protect predators, such as more targeted pesticide Figure 5. The predatory beetle, . The adult applications, predators can help keep pest populations in eats the eggs of timber beetles, and its larval stage hunts check. Studies we have conducted in infested churches have down pest larvae deep within the timber. shown that changes in the population follow changes in their prey population of death-watch beetles. However, it remains to be seen whether proprietors of historical buildings mate and lay eggs, breaking the infestation cycle. No one can overcome their arachnophobia to control the death-watch has yet discovered sex produced by the death- beetle. watch beetle, but both males and females are attracted to a range of compounds found in its preferred food, i.e. timber. Heat sterilisation It is hoped that, eventually, traps laced with the right Heat sterilisation is currently receiving a lot of attention. It compounds will provide yet another tool for the integrated is claimed that a temperature of 52–55°C maintained for management of timber pests. 30–60 minutes will kill all wood-boring insects. Given that Through our research, several essential facts about the live death-watch beetle larvae have been found in the middle death-watch beetle are now better understood. This of large, recently fire-damaged timbers, the duration of information can be used to develop cost-effective and envi- treatment would need to be much longer than one hour if ronmentally sustainable control strategies for historical this temperature is to be achieved throughout a 300 × buildings with timber pest problems. The main hurdle now 250mm oak member, for example. The potential effects on faced is one of putting theory into practice. For IPM in delicate finishes, oak panelling and other fragile fabric of buildings to work, the pest control industry requires better such a temperature for a prolonged period are likely to be education so that pest control operators can recognise active considerable. infestations through monitoring and implement targeted treatments. The general public should understand that a few Light traps insects inside their buildings does not necessarily mean the Traps which use an appropriate wavelength which attracts building is structurally undermined, but if neglected, could beetles during the emergence season (late-March to late July) result in severe problems. The cornerstone of IPM in buildings can be effective in controlling beetles. The simplest and least will rely upon good building management. A healthy building expensive form of such traps is the Beetle Screen which is a sound and dry building, and good health means fewer utilises replaceable sticky sheets of paper, and is hung in a pest problems. roof space where a population of death-watch beetles is suspected. The limitation of these traps is that they rely upon the ability of the death-watch beetle adults to fly References and Further Reading towards the light and become trapped. Our research has Belmain, S. R.; Blaney, W. M.; Simmonds, M. S. J. (1998) Host shown that ambient temperatures must exceed 19°C in selection behaviour of , Xestobium rufovil- order for adult beetles to readily fly. As such temperatures losum de Geer (Coleoptera: Anobiidae): Oviposition preference can not be guaranteed during a British spring, it may be choice assays testing old vs. new oak timber, Quercus sp. Entomologia Experimentalis et Applicata, 89, 193–199. necessary to artificially increase the temperature within the Belmain, S. R.; Simmonds, M. S. J.; Blaney, W. M. (1999) infested area using space heaters which would help ensure Deathwatch beetle, Xestobium rufovillosum, in historical that the maximum number of beetles are caught. buildings: monitoring the pest and its predators. Entomologia Experimentalis et Applicata, 93, 97–104. Belmain, S. R.; Simmonds, M. S. J.; Blaney, W. M. (2000) Behavioral responses of adult deathwatch beetles, Xestobium Outlook rufovillosum de Geer (Coleoptera: Anobiidae), to light and Further efforts are being made to develop traps which are so dark. Journal of Insect Behavior, 13, 15–26. attractive to the death-watch beetle that newly emergent Birch, M. C.; Keenlyside, J. J. (1991) Tapping behavior is a adults go to their death before they have had the chance to rhythmic communication in the death-watch beetle, Xestobium

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rufovillosum (Coleoptera, Anobiidae). Journal of Insect Dr Steven Belmain ([email protected]) is a pest ecologist leading Behavior, 4, 257–263. various research projects from developing control strategies for Fisher, R. C. (1940) Studies of the biology of the deathwatch beetle, Xestobium rufovillosum de Geer. Part III. Fungal decay rodent problems in rural Mozambique to the use of insecticidal plant in timber in relation to the occurrence and rate of development materials to control insect pests in Ghana. His PhD was conducted of the insect. Annals of Applied Biology, 27, 545–557. on the biology of death-watch beetle on research conducted within Goulson, D.; Birch, M. C.; Wyatt, T. D. (1994) Mate location in the Woodcare project whilst employed at Birkbeck College, the death-watch beetle. Xestobium rufovillosum de Geer University of London. (Anobiidae) – orientation to substrate vibrations. Professor Monique Simmonds is head of the Biological Interactions Behaviour, 47, 899–907. group of the Jodrell Laboratory at the Royal Botanic Gardens, Kew. Maxwell-Lefroy, H. (1924) The Treatment of the Deathwatch She is a world expert on insect-plant interactions using tools such as Beetle in Timber Roofs. Journal of the Royal Society of Arts 72, electrophysiology to understand how plant chemistry affects insect 260-270. behaviour and physiology. Ridout, B (1999) Timber Decay in Buildings: A Conservation Approach. E & FN Spon. Dr Brian Ridout is one of the foremost timber preservation experts in Ridout, B. (in press) Woodcare and the deathwatch beetle. English Europe. His expertise in the field led him to set up his own firm, Heritage Research Transactions. Ridout Associates, offering advice, consultancy and remedial treatment for timber decay problems. He works closely with English Heritage and other bodies to assess, monitor and treat timber problems in historical buildings.

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