|BOTANICAL ELECTRONIC NEWS
|No. 443 October 4, 2011
Kendrick Brown recently joined the Canadian Forest Service (CFS) as a research scientist with expertise paleoecology and fire disturbance dynamics. Kendrick received his PhD from the University of Victoria, where his research focused on understanding the origin, evolution and dynamics of the coastal temperate rainforest complex of western North America (Brown & Hebda 2002a, 2003), including human modification of the fire regime (Brown & Hebda 2002b). Part of this research also involved quantitatively reconstructing Holocene precipitation to assess how the rainforest complex responded to past changes in precipitation (Brown et al. 2006). Through collaboration with a colleague at Delft University, Netherlands, this data is now being integrated into a hydrological model to examine how the stream flow in two forested watersheds has changed through time and in response to climate forcing.
Upon completion, Kendrick accepted a research associate position at the University of California, where he participated in a large-scale restoration project designed to convert agricultural lands into tidal freshwater wetlands. To help guide the restoration effort, a multi-proxy approach that used both sedimentological and paleoecological indicators was employed to examine the geomorphic dynamics and environmental history of the site slated for restoration (Brown & Pasternack 2004, 2005; Pasternack & Brown 2006). Subsequently, the results were integrated into a hydrological model to generate a range of restoration scenarios.
Thereafter, Kendrick accepted a post-doctoral position at Duke University, where he examined the climate history and disturbance dynamics of the Northern Great Plains (Brown et al. 2005; Grimm et al. 2011). The results revealed that generally wet conditions prevailed during the early Holocene interval. In contrast, the mid Holocene was characterised by great variability in moisture on a multi-decadal scale, with severe droughts alternating with more humid periods. Notably, a mega drought that lasted about 200 years was identified during this interval. Though wetter than the mid Holocene, the late Holocene was likewise characterised by multi-decadal climate variability, as evidenced by the discovery of a 160-year climate cycle that has characterised the interior plains of North America for millennia. During the wet phases of the cycle, fuel-dense grasslands expand and fire disturbance increases, whereas in the dry phases the grasslands contract and fire disturbance decreases.
Following his tenure at Duke, Kendrick was awarded a Marie Curie International Fellowship by the European Commission, taking him to Denmark where he worked as a senior scientific researcher at the Geological Survey of Denmark and Greenland. While in Europe, he was involved in several projects, including the characterisation of the boreal fire regime (Ohlson et al., 2011), determination of the amount of carbon stored in black carbon in Scandinavian forest soils (Ohlson et al. 2009), assessment of the historical incidence of fire in Denmark, and quantification of Holocene climate change in Denmark (Brown et al. 2011). Furthermore, he also participated in a project that examined the effect of black carbon deposition on the darkening and melting of the ice sheet margin in northeast Greenland (Bøggild et al. 2010).
As a research scientist with CFS, Kendrick is examining the various factors that influence the Canadian fire regime, with an emphasis on determining how the fire regime may change in the future (Brown 2011). Records of fire disturbance are being collected from fire prone regions, particularly in the boreal forest, across both lightning strike and precipitation gradients. In addition, charcoal records from the boreal-prairie ecotone are being analyzed to assess the role of fire disturbance at this dynamic vegetation boundary, particularly during times of climate change. Furthermore, he is also engaged in a project that is examining Pliocene-aged charcoal profiles from the Canadian high arctic that were deposited when boreal-like forests were located further north under past warm conditions.
Contact information: Kendrick.Brown@NRCan-RNCan.gc.ca
As a result of questions about pests and how they are controlled in the collection, in 2010 we prepared a poster for the meeting of the Society for the Preservation of Natural History Collections (SPNHC) in Ottawa (Catling & Mitrow 2010). Subsequent dialogue revealed that many were unaware of the climate control techniques of pest control and the problems that can occur if these techniques are not used. This was not a surprise because some recent surveys have suggested that less than half of the herbaria in developed countries are using environmental (climate control or air conditioning) methods. Here we expand on the content of our poster. A history of improvement in insect pest control at the Agriculture and Agri-Food Canada (AAFC) National Collection of Vascular Plants (acronym DAO) may be useful to know because it led to an extremely successful result.
Anyone who has visited herbaria or borrowed specimens will know that most herbaria around the world have had problems with the Tobacco Beetle, Lasioderma serricorne (F.), which feeds on dried plant material. DAO has been no exception from the early days, and specifically from 1948 until 1992 (W.J. Cody, pers. comm.; personal observation). The Tobacco Beetle is reported often as the most common and serious herbarium pest in a fairly extensive literature on pests of dried plant collections (Retief & Nicholas 1988, Kabir et al. 1996). Plants with seeds or dried nectar in flower heads (e.g Asteraceae, Brassicaceae, Caprifoliaceae, Liliaceae, Ranunculaceae, Tropaeolaceae, Capparidaceae, Nymphaeaceae, Lamiaceae, Moringaceae, some Rosaceae, Araliaceae, Apocynaceae, some Fabaceae, Scrophulariaceae, Apiaceae, Asclepiadaceae, Araceae, Solanaceae and Papaveraceae) are particularly susceptible and ferns and their allies much less so. However, these pest beetles can do serious damage to over 50% of most collections.
With vigilance over the years these problems were not serious at DAO. To prevent pests from entering the collection area, incoming specimens, gifts, loans and staff collections, were fumigated with Methyl Bromide in a fumigation chamber. The entire collection was housed in insect-proof and essentially air-tight steel cabinets, and the use of mothballs (Naphthalene) and Vapona inside cabinets could easily control pests. Paradichlorobenzene was used periodically, but was more offensive to staff and potentially dangerous in high concentrations (Shook 1995), and so was abandoned. Also during this period there was some experimentation with Drione Dust, Pyrethrins combined with silica gel to form a powder (Schofield & Crisafulli 1980). Although effective, the dust caused an asthmatic reaction in some staff and was also abandoned. In 1983 freezing was initiated to replace the Methyl Bromide fumigations, and when occasional outbreaks of Tobacco Beetles were found all specimens were removed temporarily to a freezer to assist in control. During this period experiments revealed that Tobacco Beetles could survive mothballs but were deterred by them. They could also survive freezing (as noted by others - Macklin 2009) but were killed by a rapid series of freezing and thawing events. Although these treatments appeared helpful they were not considered entirely successful. Beetles still found their way in, particularly during warm humid periods of some summers.
As a result of space limitations an automatic compactor with open shelving was installed in 1987 (Barr et al. 1987). Whenever the compactor was opened or closed many aisles would open briefly and the main aisle opened exposed an average of 540 shelves including approximately 27,000 specimens. Prior to this, opening and closing a cabinet exposed 32 shelves and average of 1600 specimens. Thus regular use of the collection was vastly increasing exposure to the flying pest insects (by at least 17 times). Within a year after compactor installment, Tobacco Beetles had become more noticeable, and this resulted in herbarium staff urgently looking for solutions. The best that was available at the time was Integrated Pest Management (IPM) using chemical control with physical measures such as sealing to prevent entry, quarantine and freezing (Croat 1978, Story 1985, Hall 1988).
It was in June 1989 that climate control was first recommended to the administration. It had been noticed that some air conditioned collections had much less of a problem with pests, but there was also data available from other sources. As it happened entomologists had been studying the ecology of the Tobacco Beetle for some time in an attempt to control it as a major pest of tobacco and stored food products. Through a survey of the literature, a climate control plan developed quickly; the scientific justification read: "(1) climate control has been widely recommended to control Lasioderma serricorne (e.g. Desmarchelier 1988); (2) Relative humidity less than 43% would prevent growth of larvae (e.g. Ebeling 1974) and would reduce the survival period of adults (Khan 1983); (3) L. serricorne grows 4 times faster at 30° C than at 20°C (e.g. Nilho 1984)."
This recommendation was clever but not entirely new and certainly long overdue. As a result of serious damage to tobacco, there were actually many references to control by temperature, some as early as the 1930s (Crumb & Chamberlain 1934, Swingle 1938). In 1975 Ebeling wrote, "The minimal temperature for development was about 18°C (65°F) and food stored below that temperature was found to be safe from infestation." The effectiveness of temperature (environmental control) as an alternative to fumigation for protection of food and tobacco has been mentioned many times since (Imai & Harada 2006). However, the development of chemical pesticides had a strong influence and this remained a widespread method of control over many centuries.
Until the climate control could be installed in 1992, a number of interim measures were taken. Pyrethrin insecticides were used with limited success, followed by Dichlorvos (DDVP, trade name - Vapona) in form of strips and regular fumigation with DDVP smoke bombs. These measures were potentially hazardous to staff and expelling fans were installed to reduce staff exposure. Experiments during this period revealed that not all insects were affected by Dichlorvos treatments, presumably as a result of the treatment times (weekends when staff were away being insufficient to deliver poisonous air to all isolated air pockets between sheets in all parts of the collection. Recently it has been shown that Dichlorvos exposure may impede extraction and amplification of DNA from museum specimens (Espeland et al. 2010), so these actions were both ineffective and damaging to specimens.
Specimens in parts of the collection where Tobacco Beetles had been present and that were especially susceptible (Asteraceae etc. - see above) were consecutively frozen and thawed and put in plastic bags. This was mostly effective. Also humidity was monitored, and when it reached high levels, portable humidifiers were installed to achieve lower levels that would curtail development of Lasioderma serricorne. Beetles were monitored with sticky card traps. The monitoring suggested relatively effective control but the time required to implement these controls made the start of climate control in 1992 a very, very welcome event.
It seems remarkable that the least expensive and safest (for people and the environment) methods of pest control were generally known in the 1930s but not implemented in herbaria for 60 years. Such was our confidence and satisfaction with poisons. As recently as 1988, when Hall reviewed pest control methods in herbaria, the use of low temperature to control Tobacco Beetles was still not widely known, nor was it featured by Strang in his otherwise useful 1999 review. It was sometime later that only some of the literature mentioned temperature as a worthwhile control measure, and even this did not mention experience in herbaria. Mallis (1997) for example alluded to Crumb & Chamberlain's (1934) article on the effectiveness of storing cigars at 13°C (55°F). Penniger (1994) alluded to the value of low temperatures but without specific information, and in his later references (Penninger 1998), he focused on lethal temperature control. In some cases climate control techniques might be confused with "thermal control" which is involves exposing insects and specimens to high or low temperatures (Strang 1999) such as +55°C (131°F) or - 20°C (-4°F), which may damage the specimens. This is sometimes called "control with lethal temperatures" and it is intended to kill pests. Environmental (or climate control) utilizes low temperatures that prevent pest activity. Pests become inactive and eventually die, but pupae or eggs may remain viable for long periods. The effectiveness of environmental control is based on the continuous maintenance of cool conditions.
Climate control measures at the DAO herbarium involve continuous exposure to 16°C (61°F). This has the added benefit of maximizing the preservation of paper and specimens which are best maintained by low, non-fluctuating temperatures and low humidity (e.g. Hill 1999; Balazic et al. 2007). In general the control of pest insects in museums (those feeding on wood, cotton, silk, skins, plant material, etc.) is controlled by a temperature of less than 15°C (59°F) where reproduction stops and movement is substantially decreased (Child 2007).
Since the implementation of climate control in 1992 in the DAO herbarium, the total success has been reflected in five ways: (1) no insect pests have been found in the collection; (2) a substantial amount of money has been saved on costly fumigations and other procedures; (3) there have been great savings in time; (4) achieved complete safety for staff and visitors; (5) reduced environmental impact; and (6) use of best practices for preservation of archival materials.
In the early 1990's, the Royal British Columbia Museum in Victoria undertook an extensive program of removal of asbestos from their buildings. At that time, the contents of the RBCM herbarium (V) had to be moved to the area behind the public exhibits, where the herbarium specimens would have been exposed to possible (and highly probable) insect attacks. In order to protect herbarium specimens, the specimen bundles from each shelf were wrapped in clear plastic bags. The bags used were clear flat polyethylene bags, 56cm wide and 91.5cm long, 3 mill thick.
After the renovation of the original herbarium space, the herbarium collection was moved back to the original herbarium cabinets on movable compactors. The use of polyethylene bags has been retained even after the move of the herbarium back to its permanent site.
The advantage of this technique is that any insect infestation is limited to the content of a single shelf of the herbarium cabinet. The disadvantage is that the users have to be careful when folding the top of the polyethylene bag under the base of bagged specimens. Handling of herbarium specimens is more difficult, since this technique adds a slight inconvenience when removing specimens from the polyethylene sleeve and returning them to the sleeve. I have met several top Canadian botanists who complained about this and even refused to work with the RBCM herbarium specimens. I believe, however, that this small annoyance is outweighed by the advantages that this technique brings to pest control in the herbaria, namely the possibility of early detection of insect infestation and the ability to isolate this problem to a single herbarium shelf. In my opinion, the end clearly justifies the means.
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