Environmental Implications of Two Introduced Ambrosia Beetles
The environmental implications of two introduced ambrosia beetles in British Columbia
by
EVELINE STOKKINK
A thesis submitted in partial fulfillment of the requirements for the degree of
MASTER OF SCIENCE in ENVIRONMENT AND MANAGEMENT
We accept this thesis as conforming to the required standard.
Dr. Charles Krusekopf, MEM Program Head School of Environment and Sustainability
Dr. Leland. M. Humble, Research Scientist Natural Resources Canada, Canadian Forest Service
Dr. John H. Borden, Chief Scientific Officer Phero Tech International
Dr. Tony Boydell, Director School of Environment and Sustainability
ROYAL ROADS UNIVERSITY
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Abstract
Recent surveys in southwestern British Columbia, Canada have found that introduced wood- boring ambrosia beetles are a major component of the ambrosia beetle fauna. This study focuses on two recent introductions, Trypodendron domesticum (Linnaeus) and Xyloterinus politus (Say). Traps, baited either with a host -produced kairomone (ethanol) and the
T. lineatum aggregation pheromone, "lineatin", (an attractant utilized by several Trypodendron spp.), or ethanol alone, were used to capture insects and determine their seasonal occurrence, their distribution and expansion in BC and their presence in and around timber processing sites. The results increase the knowledge base on the biology and distribution of these two species. Environmental Implications of Two Introduced Ambrosia Beetles iii
Acknowledgements
My dream, to complete a Science degree, became reality thanks to the support of many people.
I am indebted to Lee Humble who agreed to be my supervisor, Vivian Wilson who took a
chance and accepted me into the MEM program and to Phero Tech International, Delta, BC,
who provided me with the lures needed for both years of study.
It wouldn't have happened without Leslie Chong, whose expertise in beetle identification and
willingness to help provided me with invaluable data. I also am indebted to my friends and
family, especially Doug Henderson, Christa Hrabok and Ben Chalmers, who encouraged me,
fed me and worked for and with me so I could attain this goal.
But most of all, I am honored and appreciative to have caught the eye of John Borden. Many
years ago, John saw a spark in an 18-year old Simon Fraser University student. He never gave
up on her, even when she gave up on herself. John, for all the encouragement, support,
commitment and enthusiasm you have provided over the past 40 years, "this one's for you!" Environmental Implications of Two Introduced Ambrosia Beetles iv
Table of Contents
Abstract ii
Acknowledgements iii
Table of Contents iv
List of Figures v
List of Tables v
Introduction 1
Literature Review 3 Economic and ecological ramifications 3 Introduced Ambrosia Beetles 4 Indigenous ambrosia beetles in the natural system 5 Impacts of indigenous ambrosia beetles 5 Ambrosia beetle management 7 Pheromone and trap development 8 Trypodendron domesticum (Linnaeus) 9 Xyloterinus politus (Say) 10 Distribution of T. domesticum and X. politus in western North America 12
Method 13 Geographic distribution 13 Seasonal flight activity 18
Results 19 Geographic distribution 19 Seasonal flight activity 21
Discussion 30
Recommendations 38
References 40 Environmental Implications of Two Introduced Ambrosia Beetles v
List of Figures
Figure 1: Map showing monitoring trap locations for T. domesticum and X. politus in southwestern BC 20
Figure 2. Seasonal distribution of captures of T. lineatum and T. domesticum at Simon Fraser University 22
Figure 3. Seasonal distribution of captures of T. lineatum and T. domesticum at Malcolm Knapp Research Forest 26
Figure 4. Seasonal distribution of captures of G. sulcatus and X. politus at Malcolm Knapp ResearchForest 27
List of Tables
Table 1. Detailed description of 29 BC trapping locations in 2004 or 2005 17
Table 2. Captures of X. politus and T. domesticum in 2004 and 2005 at locations beyond the known range of either species in 2001 ,.20
Table 3. Comparison of numbers of native and introduced ambrosia beetles captured in 2004 in multiple-funnel traps with two different lures in two locations in the lower mainland of BC 22 Environmental Implications of Two Introduced Ambrosia Beetles 1
Introduction
Improvements in transportation technology over the last century have greatly enhanced the mobility of people and the trading capacity of nations. However, they have also increased the potential for serious ecological problems, one of which is the introduction of non-native species into foreign ecosystems and environments. Fuchs (2001) stated that "biological invasions are among the most serious modern ecological problems". In addition to the impacts that non-native species can have on economic, cultural, intellectual, aesthetic and spiritual values important to society, they can cause important changes in biodiversity and alter ecosystem function. Most arrive at their new location without the predators, pests, parasites and pathogens that keep populations in control in their native habitat (Allen & Humble, 2002).
Without these natural control agents, non-native species sometimes thrive and cause great impact in their new environment. This thesis pertains to two non-indigenous ambrosia beetles,
Trypodendron domesticum (Linnaeus) and Xyloterinus politus (Say) (Coleoptera:
Curculionidae: Scolytinae), introduced into a new geographical range on the Pacific Coast of
British Columbia.
Not all introduced species become problematic. Successful establishment is dependent upon many factors, including the numbers introduced, availability of hosts, adaptability of the organism, and the level of competition in the new habitat. Statistically, the probability of an invasive species moving from an 'introduced' organism to 'pest' (any species, strain or biotype of plant, animal or pathogenic agent injurious to plants or plant products (FAO, 2007)) involves three leaps often. Williamson and Fitter (1996) suggest that "one in ten introduced species escapes into the wild; one in ten of these becomes established and one in ten of those Environmental Implications of Two Introduced Ambrosia Beetles 2 that establish becomes a pest". I suggest that introduced species need not become economically important pests before they have a significant impact on an ecosystem.
The status of "significant pest" is usually given to an insect once it is known to have an economic impact. This can be in a general sense, e.g. reducing the contribution of British
Columbia's forest industry to the gross domestic product, or in a specific sense, e.g. degrading the value of saw logs. Before this threshold is reached, an invasive insect could already have infiltrated and irrevocably altered its environment, preventing possible control or containment.
Because such insects are often not pests in their native environment, they are often not well studied. Therefore, basic biological knowledge of the species may be lacking, and is not available to be used in development of management strategies for invasive species management. This situation may be exacerbated by the fact that biological changes may occur as an invasive species adapts to its new environment.
The necessity for in depth information prompted the questions addressed in this thesis.
My objectives were: 1) to determine if T. domesticum (Linnaeus) and X. politus (Say) are expanding their geographical range in BC; 2) to assess whether either or both of these species exist in part or all of their new range in comparable numbers to native species; and 3) to compare season-long catches of flying beetles to evaluate whether flight periods of
T. domesticum and X. politus are separate from or overlap those of indigenous ambrosia beetles. Environmental Implications of Two Introduced Ambrosia Beetles 3
Literature Review
Economic and ecological ramifications
Canadian forests are a major economic contributor to the gross domestic product, and forest products are a major export commodity (Krcmar-Nozic, Wilson, & Arthur, 2000). Any threat to this economic resource, due to deteriorating forest health, export restrictions, insect control costs, or loss of biodiversity could jeopardize Canada's position in the global market.
Introduced species often enter into ecosystems already stressed by human activity (Krcmar-
Nozic, et al., 2000). Entering a new habitat, which doesn't have any of the checks and balances present in their native habitat, often provides introduced species with a distinct advantage over local insect populations. Over time, this could lead to the suppression or displacement of competing native species (Marchant & Borden, 1976).
The availability of new host plant species may provide an introduced phytophagous insect with new opportunities. A new host may offer a more suitable habitat than those of the insect's native range, and the insect may focus exclusively on this host, turning from a generalized insect into a specific pest (Marchant & Borden, 1976). Often this is attributed to the absence of co-evolution between the insect and its new host, which has not been subjected to selection pressure to develop adaptive defenses to the introduced species. Recent examples of introduced insects that have had a significant impact on hosts with which they have not co- evolved include the brown spruce longhorned beetle, Tetropium fuscum (Fabricius) on spruce,
Picea spp., in Nova Scotia (Sweeney, Gutowski, Price & de Groot, 2006), the emerald ash borer, Agrilus planipennis Fairmaire, on ash, Fraxinus spp., in the lake states and Ontario Environmental Implications of Two Introduced Ambrosia Beetles 4
(McCullough & Siegert, 2007), and the red turpentine beetle, Dendroctonus valens (LeConte),
on pines, Pinus spp., in China (Sun et al., 2003).
A key factor to successful introduction is the opportunity to enter into a new area undetected.
Ambrosia beetles have long been recognized as some of the most easily introduced insects
(Haack, 2003; Marchant & Borden, 1976). They are commonly found in association with
food, packing materials, logs, lumber and nursery stock (Wood, 1982). Their cryptic habitat
in galleries deep in the wood of imported logs, lumber and dunnage make detection difficult.
Introduced Ambrosia Beetles
The role that introduced ambrosia beetles play within British Columbia's forest ecosystems is
not yet clear. Recent surveys around urban and managed forest sites in southwestern BC have
uncovered a rich and diverse population scolytid beetles (Henry, 2004; Humble, 2001).
Humble (2001) has discovered that nine introduced ambrosia beetles are now established in
BC. Little is known about the biology, distribution and impact of most of these species.
Trypodendron domesticum, native to Europe, and X. politus, an eastern North American
ambrosia beetle, were already well established when they were discovered in British Columbia
(Humble, 2001). Both species have demonstrated their ability to adapt to new environments
and hosts; T. domesticum by its apparent newly-acquired ability to attack healthy beech trees,
Fagus sylvatica L., in Southern Belgium (Henin, Huart, Lejeune, Rondeux, 2002; Kuhnholz,
Borden, & Uzunovic, 2001) and red alder, Alnus rubra Bong., in BC (Humble, 2001), and X. politus by adapting to a new host, western hemlock, Tsuga heterophylla (Raf.) Sarg. in BC
(Henry, 2004). Environmental Implications of Two Introduced Ambrosia Beetles 5
Indigenous ambrosia beetles in the natural system
Ambrosia beetles are often considered as 'nature's recyclers' (Borden, 1988), as they perform the important ecological role of initiating and promoting nutrient recycling (Lindgren, 1990).
They usually invade dead or dying trees, and the ambrosial fungi, which they introduce into the wood and later feed on, starts the slow process of breaking down the cellulose-based substrate.
Their entrance holes provide access to other wood-infesting insects and fungi that continue the decomposition process.
Ambrosia beetle populations are dependent on the availability of suitable habitat, which in a natural setting, occurs sporadically as blowdown and winter-killed trees (Borden, 1988). It has only been since the advent of large scale logging and sawmilling, with extensive forest rights-of-way, clear-cuts, dryland sorts, booming grounds and storage yards full of unseasoned freshly-sawn lumber that these insects have become problematic.
Impacts of indigenous ambrosia beetles
Stockpiling logs for future processing creates an unnatural increase in the concentration of host material. As a result, beetle populations increase, especially at log storage sites such as dryland sorts and boom tie-ups. Once logs are attacked and gallery construction commences, the fungus-produced stain in the wood surrounding the gallery degrades the value of a log and the lumber derived from it. To maintain a continuous, uninterrupted supply of material for sawmills, winter-felled logs are stored in cut blocks, boom tie-ups and at dryland sorts. These storage sites support healthy populations of several native species, primarily Trypodendron lineatum (Olivier), Gnathotrichus sulcatus (LeConte) and Gnathotrichus retusus (LeConte). In
1985, native ambrosia beetle attack on both logs and unseasoned lumber, primarily in high Environmental Implications of Two Introduced Ambrosia Beetles 6 value coniferous sapwood, cost the coastal lumber industry approximately $63 million annually (McLean, 1985). Using updated market values, this figure had increased to $200 million five years later (Lindgren, 1990). When infested logs are detected in a sawmill, cutting patterns are often modified to separate infested sapwood from unattacked wood, raising the cost of milling and lowering the overall value of lumber derived from an infested log (Orbay,
McLean, Sauder & Cottell, 1994).
Extra milling costs and degrade are not the only issue. When purchasing green lumber, buyer apprehension over the possibility of importing and introducing these species into new environments can generate additional inspection charges, further sorting to eliminate signs of infestation (pinholes), fumigation costs and phytosanitary restrictions, bringing the concern of introduced species full circle.
Trypodendron lineatum is the most economically important of the native ambrosia beetles, due in part to its tendency to concentrate in high numbers on host logs and its habit of overwintering in forest margins close to the natal host. This behavior intensifies beetle populations around permanent log storage sites or sorts. As beetles emerge from their overwintering habitat in the forest, logs in the adjacent storage sites are available for attack.
Later in the season many incoming logs, attacked before transport to the storage area, release brood while on the sort. These brood adults fly to the adjacent forest to overwinter, augmenting the local beetle population already present. These beetles provide the source population for attack the following spring.
In contrast to T. lineatum, both G. sulcatus and G. retusus overwinter in brood logs and, in the spring, attack fresh hosts upon emerging from their natal gallery. The main flight of G. retusus Environmental Implications of Two Introduced Ambrosia Beetles 7 occurs in May-June, while G. sulcatus can have two dispersal flights, one in May-June and another in the autumn (McLean & Borden, 1979). If the dispersal flight occurs when logs are held in a storage area, previously unattacked logs can become infested. Of the three species,
G. sulcatus most commonly attacks freshly-sawn lumber (McLean & Borden, 1979), and because it can complete its life cycle in this commodity (McLean & Borden, 1975), it represents a major threat of introduction into lumber-importing countries.
Ambrosia beetle management
Economic losses from indigenous ambrosia beetles prompted research into how these insects could be managed. Control measures in the early 1950's consisted of spraying logs, booms and unseasoned lumber, first with DDT and later with lindane and methyl trithion.
Environmental concerns with spraying chlorinated hydrocarbon insecticides on log booms in saltwater inlets and fresh water lakes at the rate of lkg/ha (Borden, Chong, Gries & Pierce,
2001 ), as well as health complaints by forestry workers eliminated the use of toxic chemical insecticides as control agents (Borden, 1995).
The elimination of insecticides left logging companies with inventory management as the only recourse to suppress beetle populations. While this seems an obvious and simple control measure, it is difficult to achieve. Maintaining year-long mill inventories, coping with forest shutdowns due to fire danger or snow pack and dealing with the fluctuations of world markets demands a certain degree of inventory stockpiling (McLean & Stokkink, 1988). Hence a replacement was needed for the banned insecticides to protect stored logs and lumber from ambrosia beetle attack. Environmental Implications of Two Introduced Ambrosia Beetles 8
Pheromone and trap development
Bark and ambrosia beetles use olfactory signals to find their hosts and mates, a discovery first
made by Anderson (1948) for the pine engraver, Ipspini (Say). Graham (1968) found that
T. lineatum, as well as many other bark and ambrosia beetles, respond to the primary
kairomonal attractant ethanol, produced by anaerobic metabolism in decaying wood tissue
(Byers, 1992; Holighaus & Schiitz, 2006; Kelsey, 1994). Although pioneer adult T. lineatum
use ethanol as an attractant, mass attack is induced by the pioneer adults releasing an
aggregation pheromone (chemical that conveys a message to members of the same species)
(Rudinsky & Daterman, 1964). A decade after demonstration of the presence of an
aggregation pheromone, identification and synthesis of the pheromone 'lineatin' was finally
accomplished (Borden et al, 1979; MacConnell, Borden, Silverstein, & Stokkink, 1977). This
compound, along with ethanol and a-pinene (another host volatile) is now used in commercial
mass trapping programs.
Further research has confirmed that other Trypodendron spp. are attracted to lineatin. The
pheromone can be effectively used to attract T. domesticum and Trypodendron signatum
(Fabricius) in Europe (Payne, Klimetzek, Kohnle, & Mori, 1983), and Trypodendron
rufitarsus (Kirby) and Trypodendron retusum (LeConte) in North America (Kiihnholz, 2004).
Identification of two other aggregation pheromones, 'sulcatol' for G. sulcatus and 'retusol' for
G. retusus opened up the exciting prospect of using pheromones to manage all three species of
ambrosia beetles pests on the BC coast (Borden et al., 1980; Byrne, Swigar, Silverstein,
Borden & Stokkink, 1974). However, an effective trapping system was also needed. Prior to Environmental Implications of Two Introduced Ambrosia Beetles 9
1982, monitoring and research traps consisted of hardware cloth coated with a sticky material
(McLean & Borden, 1979). While effective, they were cumbersome and not feasible for massive suppression trapping programs. The development of a highly portable, user-friendly multiple funnel trap (Lindgren, 1983) made it possible to establish area wide trapping programs employing several hundred traps in a given location (personal experience).
Trypodendron domesticum (Linnaeus)
The native range of T. domesticum includes western Asia and Europe. Its hosts are varied and include many hardwoods such as oak, Quercus spp., beech, Fagus spp., maple, Acer spp., alders, Alnus spp., hornbeams, Carpinus spp., birch, Betula spp., mountain ash, Sorbus spp., linden, Tilia spp., cherry, Prunus spp., European chestnut, Castanea sativa, thornapple,
Crataegus spp., holly, Ilex aquifolium, apple, Malus spp., and willow, Salix spp. (Dobesberger,
2004; Wood & Bright, 1992). It is generally considered to be a secondary attacker, a species that confines its attacks to stressed, dying or recently dead trees (Kuhnholz et al., 2001).
However, it recently has been shown to attack apparently healthy beech, Fagus sylvatica (L.), in Germany (Gregoire, Piel, Proft, & Gilbert, 2001; Henin et al., 2002) as well as paper birch,
Betula papyrifera Marshall, and red alder in BC (Kuhnholz et al., 2001).
In Europe, overwintering T. domesticum emerge in early spring (March) and begin searching for suitable hosts. After the pioneer females reach a suitable host, they release lineatin
(Kuhnholz, 2004) that attracts conspecific males and females (Payne et al., 1983). Once males and females are paired, copulation follows after which the female begins gallery construction and oviposition in the xylem. Both adult beetles and their progeny feed exclusively on ambrosial fungi initially expelled from the attacking female's mycangia (fungal storage Environmental Implications of Two Introduced Ambrosia Beetles 10 structures) and which grows into the walls of the gallery (Kuhnholz, 2004). There is some evidence that more than one type of fungus is necessary for complete development (Kuhnholz,
2004). Host acceptance is based on the suitability of the wood substrate for growth of the fungus.
Ambrosia beetles that attack angiosperms appear to penetrate more deeply into the dead heartwood than those that attack conifers which are generally restricted to the sapwood
(Kuhnholz, 2004). Holighaus and Schutz (2006) suggest that different parts of attacked beech may exhibit different levels of decay, and that decayed wood unsuitable for attack can be perceived by the beetle, allowing them to avoid specific areas of otherwise suitable hosts.
There appears to be some homogeneity between the volatiles released by living trees that have experienced stress and the volatiles of felled deadwood (Holighaus & Schutz, 2006). Stresses correlated with subsequent T. domesticum attack in beech trees in Germany included a heavy frost three years prior to attack (Henin et al., 2002) and a continuous presence of "European beech bark disease" (Holighaus & Schutz, 2006). Both phenomena would likely result in anaerobic metabolism and production of the host kairomone ethanol.
The ability of T. domesticum to take advantage of a trees' vulnerability, combined with availability of new habitats and stresses induced by a changing global climate (Kuhnholz et al.,
2001) could have far reaching effects for forest ecology and timber harvesting in BC.
Xyloterinus politus (Say)
Xyloterinus politus is native to eastern North America (Bright, 1976; Wood, 1957) and while it appears to have a preference for deciduous trees, specifically beech, maple and birch (Drake, Environmental Implications of Two Introduced Ambrosia Beetles 11
1921), attack has been recorded on three conifer genera: spruce, Picea spp.; pine, Pinus spp.;
and hemlock including Tsuga canadensis (L.) (MacLean & Giese, 1967; Wood, 1982). It
prefers low-vigor trees, concentrating on diseased or recently cut hosts.
Xyloterinus politus is the only species in the genus, which is closely related to Trypodendron
(Wood, 1982). No aggregation pheromone has been identified for this species. Male X, politus
do not appear to have any role in gallery construction and are seldom observed near actively
attacking females. It is suspected that mating occurs either in the natal gallery or on the host
log before excavation occurs (MacLean & Giese, 1967). MacLean and Giese (1967) also
observed that the female initiates gallery construction and does all the work within the log
while the male limits his efforts to removing boring dust from around the entrance hole. The
lack of active participation suggests that, should an aggregation pheromone exist, it would be
produced by the female, as in Trypodendron species. Once eggs are laid, it takes about a
month to produce pupae and callow adults. Young adults continue to feed on ambrosia fungus
and with their parents, overwinter in cradle niches and galleries (MacLean & Giese, 1967).
While X. politus does not appear to attack healthy trees, its ability to attack coniferous hosts is
a cause for concern. Henry (2004) recovered X. politus from logs of western hemlock, Tsuga
heterophylla, cut and left along the forest edges in the University of British Columbia's
Malcolm Knapp Research Forest near Maple Ridge, BC. While the native species, G. sulcatus
and G. retusus were predominant, X. politus was the third most abundant species recovered
from the logs. Adult T. lineatum, although not present during excavation, were estimated by
counting the number of entrance holes. They, along with a single male Xyleborus sp., made up Environmental Implications of Two Introduced Ambrosia Beetles 12 the remaining beetle population (Henry, 2004). Western hemlock is a tree of major importance to BC's forest industry and the prospect of yet another insect species capable of affecting its economic value (and possibly that of other conifer species) is of major concern. Because no specific pheromone is available for use in monitoring or suppression programs,
X. politus populations could grow and inflict damage, while not being detected or suppressed by current pheromone-based trapping programs. Research on the chemical ecology of this species is thus urgently needed.
Distribution o/T. domesticum and X. politus in western North America
Trypodendron domesticum and X. politus have been intercepted at North American ports on several occasions (Haack, 2003; Mudge, LaBonte, Johnson, & LaGasa, 2001), and both were already established in BC when surveys for the presence of non-indigenous insects were initiated by the Canadian Forest Service (CFS) and the Canadian Food Inspection Agency
(CFIA) from 1995-1999 (Humble, 2001). The first X. politus were recovered in 1997 in
Burnaby, BC (Humble, 2001) and surveys in subsequent years confirmed its presence at many locations in the lower Fraser Valley of BC (as far east as Ruby Creek) and included a single specimen from southern Vancouver Island (L. Humble, personal communication, September,
2004). In 1997 and 1998, X. politus was also found in surveys for non-indigenous woodborers conducted in Washington and Oregon (Mudge et al., 2001).
The prevalence of T. domesticum in urban forest habitats was demonstrated in surveys conducted in 1999 along the Fraser River (Humble, 2001). At the Port Mann Landfill in
Surrey, 66% of all insects captured in lineatin-baited traps were T. domesticum. Environmental Implications of Two Introduced Ambrosia Beetles 13
The presence of forest habitats near urban importing facilities has aided the establishment of introduced ambrosia beetles in new environments. The native beetle T. lineatum is capable of flying several kilometers across valleys (Salom & McLean, 1991) and in the laboratory, has been recorded to fly for up to eight hours (Borden, 1988). Other Trypodendron spp. probably have similar capabilities. Scolytids, due to their small size, are also greatly affected by winds and are often carried great distances before finding new hosts. Other life stages are easily transported via raw logs, green lumber and previous to 2002, in untreated wood products such as dunnage and crating (Haack, 2003). In 2002, the International Plant Protection Convention
(IPPC) produced a set of guidelines for regulating wood packaging material in international trade (ISPM No. 15) which has led to treatment of all wood packaging (FAO, 2006).
Method
Geographic distribution
Trap locations were selected beyond the known range of both T. domesticum and
X. politus, where trapping programs had detected their presence in the heavily urbanized lower
Fraser River Valley east to Ruby Creek (Humble, 2001). Traps were placed along the four corridors leading into the interior of BC (Highway #3, Highway #1, Highway #5 and the Duffy
Lake Road, as well as on the Sunshine Coast, Vancouver Island, and northern and southern
Okanagan Valley (Figure 1, Table 1). Locations were chosen to include road proximity
(connection to vehicle transport of infested material) and deciduous forest cover (possible host source for both beetle species). Environmental Implications of Two Introduced Ambrosia Beetles 14
At each location, two 12-funnel Lindgren traps with semiochemical lures (Phero Tech
International, Delta, BC) were set up about 35 m apart. One trap was baited with a 40 cm ethanol lure (release rate 30 mg/day at 20 °C as determined in the laboratory) and the other with an identical ethanol lure plus a lineatin flex lure (release rate 0.02 mg/day at 20 °C).
Lures were positioned in the middle of the trap allowing maximum release of host volatiles and pheromone (Lindgren, 1983).
Traps were set in place by 15 March in 2004 and 2005; specific locations were changed each year, maximizing detection opportunities. Captured beetles were collected in late May and mid
July and were bagged and frozen for later identification and counting. Beetles were identified to species by Leslie J. Chong, an expert on Scolytinae in BC, using Bright (1976) and Wood
(1982) as definitive references. As predation or decomposition made some identification impossible, only those beetles that could be clearly identified were counted and identified to species. When small numbers of target species were present, all individuals of each species were counted directly. Volumetric estimates (80 beetles/ml) were made whenever large numbers of individuals were present. None of the catches were processed until the end of the
2005 trapping season. Voucher specimens of X. politus and T. domesticum captured beyond the geographic range established by Humble (2001) have been deposited in the reference collection at the Pacific Forestry Centre, Natural Resources Canada, Victoria, BC. Environmental Implications of Two Introduced Ambrosia Beetles 15
Figure 1: Map showing monitoring trap locations for T. domesticum and X. politus in southwestern BC. For exact locations of traps refer to Table 1. Squares indicate trapping sites where either or both species were detected in 2004 or 2005 (Table 2). Triangles indicate sites where neither species was detected. Black star (Ruby Creek) indicates previous known eastern limit of distribution of both species. Environmental Implications of Two Introduced Ambrosia Beetles 16
Figure 1. Environmental Implications of Two Introduced Ambrosia Beetles 17
Table 1. Detailed description of 29 BC trapping locations in 2004 or 2005 (Figure 1).
Site Description Trapping Year Elevation (m) Longitude Latitude
Eastgate Service and General Store, Manning Park 2004 1020 49° 08' 09.54"N 120° 37' 04.00"W 2.8 km east of East gate, Manning Park 2005 1013 49° 09' 05.55"N 120° 36' 04.28"W Weyerhaeuser Canada Ltd., Maple Street, Okanagan Falls 2005 371 49° 20' 03.00"N 119°33'51.54"W Riverside Forest Products, Hwy #6, Lumby 2005 378 50°15'40.32"N 119° 16' 14.96"W 25.7km east of Hope, on Hwy. #3 2004 665 49° 15' 43.50"N 121°11'57.22"W Sunshine Valley, 22 km east of Hope, Hwy. #3 (WES1) 2005 674 49° 16' 19.25"N 121° 13' 38.37"W Coquihalla Toll Plaza, Hwy. #5 2004 1221 49°35'41.65"N 121° 07' 27.98"W 4 km west of Coquihalla Toll Plaza, Hwy. #5 2005 573 49°29'45.53"N 121°12'25.57"W Gas station before bridge at east boundary of Yale (YAL) 2004 89 49° 33' 45.72"N 121°25'05.07"W 5 km south of Yale (Hope River General Store) (YAL1) 2005 63 49° 33' 48.47"N 121° 25' 34.62"W Boston Bar First Nation Sort Yard, North Bend (NOR) 2004 126 49° 52' 35.58"N 121° 26' 47.06"W Abandoned site of the J. Jones dryland sort, Boston Bar 2005 138 49°51'37.48"N 121° 26' 39.00"W Lytton Lumber Ltd., Lytton 2004 210 50°13'11.99"N 121° 34' 36.41"W Ainsworth Lumber Co., Seton Lake Rd., Lillooet 2004 199 50°40'41.27"N 121°56'09.20"W Field behind Lightfoot Gas, Lillooet 2005 210 50° 40'33.05"N 121°56'03.18"W 20 km east of Pemberton on Duffy Lake Rd. 2005 295 50° 17' 47.44"N 122° 35' 00.60"W Continental Log Homes, Pemberton 2005 212 50° 19' 02.82"N 122° 42' 46.10" W Green River Sort, Pemberton 2004 232 50° 17' 44.88"N 122° 45'26.28"W Pemberton Valley 2005 223 50° 24' 43.52"N 122° 53'45.02"W Empire Logging, Squamish 2004 15 49°41'10.57"N 123° 09' 06.65"W Saltery Bay, Powell River 2004 37 49° 45' 55.07"N 124° 18' 34.54"W Twin Creeks Road, Gibsons 2004 28 49° 28' 45.07"N 123° 29' 09.69"W Across booming ground from Twin Creeks Sort, Gibsons 2004 17 49° 28' 33.26"N 123° 27' 08.64"W Port McNeill Upper Sort, Western For. Prod., Port McNeill 2004 85 50° 34' 34.27"N 127° 06' 33.92"W Menzies Bay Dryland Sort, Western For. Prod 2004 30 50° 06' 54.84"N 125° 22' 52.39"W North West Bay Dryland Sort, Nanoose Bay 2004 18 49° 17' 49.57"N 124° 12' 55.97"W Jemico Enterprises Dryland Sort, Chemainus 2004 62 48° 54' 28.37"N 123°44'42.02"W China Creek Dryland Sort, Port Alberni 2004 18 49° 09 '20.92"N 124°47'27.35"W Sarita Dryland Sort, on road to Bamfield 2004 22 48° 52' 57.78"N 125° 02' 06.40"W Environmental Implications of Two Introduced Ambrosia Beetles 18
Seasonal flight activity
To determine the spring flight season for each species, three pairs of 12-funnel Lindgren traps were set up on 9 February, 2004 at the University of British Columbia's Malcolm Knapp
Research Forest, Maple Ridge, BC, and three more pairs at Simon Fraser University, Burnaby,
BC. Trypodendron domesticum and X. politus had previously been collected at both locations.
Trap sites were situated near to deciduous (angiosperm) trees, the primary hosts of both
T. domesticum and X. politus. Trap pairs were placed at least 35 m apart, and traps within pairs were 15 m apart. One trap of each pair was baited with ethanol and the other with ethanol and lineatin, as in the geographic distribution study. Traps catches were collected weekly until July
20 and captured insects were kept frozen until all ambrosia beetles could be identified to species and counted. Daily temperature records were obtained from Environment Canada weather stations at both locations.
Mean catches between traps baited with ethanol or ethanol plus lineatin were compared by t-test, or when the variances across groups were not equal, by the Welch ANOVA test. In all cases a =
0.05. Environmental Implications of Two Introduced Ambrosia Beetles 19
Results
Geographic distribution
In two years of trapping, 91,339 ambrosia beetles were captured. The most common ambrosia beetle trapped was the native T. lineatum (87,215 beetles), accounting for 95.48% of all beetles captured. The remaining 4,124 beetles (4.5%) were divided between T. rufitarsus (26%), fragments of T. lineatum or T. rufitarsus pieces (10.8%), T. retusum (12.65%), Gnathotrichus spp. (2.35%), and the target species X. politus and T. domesticum (1.07%).
Catches in traps baited with ethanol + lineatin were 2.7 times greater than in traps baited with ethanol. Catches of T. lineatum were significantly different between lure types (t = 0.0185, df =
53, a, 0.05).
Both X. politus and T. domesticum were captured beyond their previously known geographic range in BC (Table 2). Xyloterinus politus was found in three locations and in both years of trapping while T. domesticum was found in two locations in 2005. Most X. politus were caught at
Yale locations, 20 and 25 km northeast of Ruby Creek, but four specimens were captured at
North Bend, a further 35.8 km north by road in the Fraser Canyon from Yale. Twenty of the 24 captured X. politus were in ethanol-baited traps. One T. domesticum was captured at one Yale location, and 15 more were 24 km east of Ruby Creek along Hwy #3. The positive trap was situated next to deciduous forest margin, close to the highway. All T. domesticum were in traps baited with ethanol + lineatin. Environmental Implications of Two Introduced Ambrosia Beetles 20
Table 2. Captures of X. politus and T. domesticum in 2004 and 2005 at locations beyond the known range of either species in 2001.
Number of Beetles Captured
Location1 Year Lure X. politus T. domesticum
(YAL) Gas station before bridge at 2004 ethanol 1 0
East boundary of Yale ethanol + lineatin 0 0
(YAL1) 5 km south of Yale 2005 ethanol 16
(Hope River General Store) ethanol + lineatin 6
(NOR) Boston bar First Nation 2004 ethanol 0
Sort Yard, North Bend ethanol + lineatin 0
(WES1) Sunshine Valley, 22 km 2005 ethanol 0 0
East of Hope, Highway No. 3 ethanol + lineatin 0 15
1 - acronyms used given in Figure 1 Environmental Implications of Two Introduced Ambrosia Beetles 21
Seasonal flight activity
Traps at SFU captured 6,776 scolytid beetles, of which 69.6% were T. domesticum. Traps at the
Malcolm Knapp Research Forest (MKRF) caught 42,020 scolytids, of which 93 % were
T. lineatum. At both locations, T. lineatum showed a significant preference for traps baited with ethanol and lineatin, as did T. domesticum at SFU (Table 3). Xyloterinus politus was captured in small numbers, only at the Research Forest, and did not show a significant preference for traps baited with either lure. In contrast, 2.5 times more G. sulcatus were captured in traps baited with ethanol and lineatin at the Research Forest then in traps baited only with ethanol (Table 3).
Trypodendron domesticum was captured in the first trapping period (February 9-16), when the maximum temperature at SFU was only 12° C. The first T. lineatum was not captured until three weeks later (Figure 2). Fifty-five percent of T. domesticum were captured up to the time the first
8.2% of T. lineatum were caught. By April 27, 90 % of the T. domesticum had flown while it took until June 22 for T. lineatum to reach the same percentage of emergence. Eleven percent of the total T. lineatum emergence occurred during the weeks of June 1-8 (4%) and June 15-22
(7%), when maximum temperatures reached >25°C. Environmental Implications of Two Introduced Ambrosia Beetles 22
Table 3. Comparison of numbers of native and introduced ambrosia beetles captured in 2004 in multiple-funnel traps with two different lures in two locations in the lower mainland of BC.
Species Location' Lure Total Beetles Mean ±SE Statistical Significance
T. lineatum SFU Ethanol 94 31.3 ±4.7 Ethanol + Lineatin 3,196 1,065.3 ±240 NS ( t = 1.3691, df=l, 4, P= 0.2428)
MKRF Ethanol 20,170 6,723.3 ± 5,810 Ethanol + Lineatin 58,210 19,403.3 ±7,210 ** f F = 4.3303, df=1, 4, P= 0.0439)
T. domesticum SFU Ethanol 1,473 491.0 ±120.0 Ethanol + Lineatin 7,816 2,605.3 ± 330.0 * (t = 5.9802, df = 1, 4, P= 0.0039)
MKRF Ethanol 20 6.67 ± 3.7 Ethanol + Lineatin 34 11.3 ±3.7 NS ( t = .8890, df= 1,4, P= 0.4242)
G. sulcatus SFU Ethanol 0 0.0 ±0 Ethanol + Lineatin 30 10.0 ±8.1 NS ( t = 1.2370, df = 1, 4, P= 0.2837)
MKRF Ethanol 1,406 486.7 ± 380 Ethanol + Lineatin 3,490 1,163.3 ±420 NS ( t = 1.2305, df = 1, 4, P= 0.2859)
X. politus SFU Ethanol 6 2.0 ±1.2 Ethanol + Lineatin 0 0.0 ±0 NS (; t = -1.7321, df= 1,4, P= 0.1583)
MKRF Ethanol 48 16.0 ±1.2 Ethanol + Lineatin 74 24.7 ± 8.8 NS (1F = 0.9744, df = 1, 4, P= 0.4297)
a SFU = Simon Fraser University, Burnaby, BC; MKRF = Malcolm Knapp Research Forest, Maple Ridge, BC.
b Asterisk by paired means indicates significant difference (t-test, P<.0.05). NS = not significant.
c Double asterisk by paired means indicates significant difference using Welch ANOVA instead of t-test, allowing for unequal variances across groups. Environmental Implications of Two Introduced Ambrosia Beetles 23
Figure 2. Seasonal distribution of captures of T. lineatum and T. domesticum at Simon Fraser
University, Burnaby, BC. Maximum temperature during each collection period (A), mean T. lineatum catch/trap (3 traps) for each lure (B) and mean T. domesticum catch/trap (3 traps) for each lure (C). Environmental Implications of Two Introduced Ambrosia Beetles 24
Feb. March 100 B Trypodendron lineatum H Ethanol D Lineatin plus ethanol 75 H o -i—• oCO Q. CO 50 H c cd 25 H nn n 1 ELEL JL n 0 17 ' OA24 I no0 2I 'n o0 9I IR' I1 6 ' 23 ' 30 06 ' 13 ' 20 ' 2l7 0l4 ' 1 1 ' 18 ' 25 01 ' 08 ' 15 ' 22 ' 29 06 • 13 • 20 Feb.' March April May June July 300 Trypodendron domesticum 250 • Ethanol • Lineatin plus ethanol
•i 200 o §" 150 S 100
50 n n fl. n .Jl. -. n. - 0 13 ' 20 ' 27 I 04 ' 11 ' 18 ' 25 I 01 ' 08 ' 15 ' 22 ' 29 I 06 ' 13 ' 20 Feb. March April May June July Environmental Implications of Two Introduced Ambrosia Beetles 25
At the UBC site, although the overall T. domesticum catch at was very low, a similar emergence pattern materialized (Figure 3). T. domesticum flight began during the week of February 24 -
March 2 and by March 16, 55% of the flight had occurred. During the same period, less than 1% of T. lineatum had flown. As in the SFU experiment, the majority of T. domesticum (90%) had emerged by April 27, while T. lineatum did not reach the same threshold until June 22. There was a similar spike in the T. lineatum catch during the weeks of June 1-8 (9%) and June 15-22
(17%) when the maximum temperatures reached >25°C. Temperatures were generally one or two degrees higher at UBC during every trapping period although the dense coniferous canopy kept the ambient temperature around the traps several degrees cooler. Although catches were low, the similarity of emergence behavior found at SFU and UBC removed the probability that the UBC catches were affected by chance.
Xyloterinus politus was not captured until the maximum temperature reached 17°C (Figure 4). Its flight coincides with that of G. sulcatus.
In most cases, high or low catches in a given week corresponded to high or low mean maximum temperatures during that week (Figures 2 - 4). Environmental Implications of Two Introduced Ambrosia Beetles 26
Figure 3. Seasonal distribution of captures of T. lineatum and T. domesticum at Malcolm Knapp
Research Forest, Maple Ridge, BC. Maximum temperature during each collection period (A), mean
T. lineatum catch/trap (3 traps) for each lure (B), mean T. domesticum catch/trap (3 traps) for each lure
(C). Environmental Implications of Two Introduced Ambrosia Beetles 27
Feb. March 2500 B Trypodendron lineatum 2000 H • Ethanol • Lineatin plus ethanol o CO o 1500 Q. Cti iiooo CO CD 500-
0- .J1.d1.dl xuQ 17 ' 24 I 02 ' 09 ' 16 ' 23 ' 360 ' I1 30 '6 2 '0 1' 32 7' 2004 '2' 171 I' 04 ' 11 ' 18M ' 25 I 01 ' 08 '15 '22 '29 I 06 ' 13 '20 Feb. March ' April ' May ' June ' July 10- Trypodendron domesticum 8 I Ethanol D Lineatin plus ethanol O CO o 6 Q. CO s_ -I-c' 4 CO CD 2
Hi ll d l_ 0- 17 ' 24 |~02 '~09 ' 16 '~23 30 I 06 ' 13 ' 20 ' 27 I 04 ' 11 ' 18 ' 25 I 01 ' 08 ' 15 ' 22 ' 29 I 06 ' 13 ' 20 Feb.' March April May June July Environmental Implications of Two Introduced Ambrosia Beetles 28
Figure 4. Seasonal distribution of captures of G. sulcatus and X. politus at Malcolm Knapp
Research Forest, Maple Ridge, BC.
Maximum temperature during each collection period (A), mean G sulcatus catch/trap (3 traps) for each lure (B), mean X. politus catch/trap (3 traps) for each lure (C). Environmental Implications of Two Introduced Ambrosia Beetles 29
Feb. • March 200- B Gnathotrichus sulcatus 160H • Ethanol • Lineatin plus ethanol o CO o 120 Q. CO
co 80 CD 40 H
0 17 ' 24 I 02 ' 09 ' 16 ' 23 ' Feb.' March 15- Xyloterinus politus Ethanol D Lineatin plus ethanol
O Sto ioH o Q. (0 c CO CD 5H
«un 0- 17 ' 24 I 02 ' 09 ' 16 ' 23 ' 30 I 06 ' 13 ' 20 11 ' 18 ' 25 I 0l 1n o' I 018R 'I 15 ' 22 ' 29 | 06 ' 13 ' 20 Feb. March April May June July Environmental Implications of Two Introduced Ambrosia Beetles 30
Discussion
Trypodendron domesticum and X. politus have proven their ability to adapt and change. They are now known to be established throughout the lower mainland and along two corridors into the interior of BC (Hwy #3 and Hwy #1). Because previous monitoring for these species did not occur further east than Ruby Creek (Humble, 2001), my study cannot confirm that the new locality records represent a recently expanded range. Angiosperm trees are abundant along these corridors, so the beetles should be able to find enough suitable host material to continue their life cycle. The four corridors were chosen specifically as they are major transportation routes for logging trucks and train cars which move logs and lumber from the lower Mainland into the interior. Other routes, such as the Capilano River and Harrison Lake with their contiguous source of deciduous forest cover, are also excellent pathways for the beetles but were not monitored during this study.
My results did not confirm that X. politus is established on southern Vancouver Island, despite
Humble's (L. Humble, personal communication, September, 2004) collection of a single specimen in that region. The apparent absence of either beetle on Vancouver Island, along the
Duffy Lake Road and the Sunshine Coast is most likely due to the lack of movement of infested logs and material from the lower Mainland into these areas. Vancouver Island, the Sunshine
Coast and the Pemberton Valley all have abundant angiosperm trees, and should be prime habitat for both species. If they expand their range into these locations, local companies may be severely affected by value loss to hardwood forest products, e.g. red alder harvested by Western Forest
Products' Stillwater Division on the Sunshine Coast. The apparent absence of either species at many of the tested locations may instill a feeling of complacency, reducing the urgency to Environmental Implications of Two Introduced Ambrosia Beetles 31 monitor for range expansion. Other introduced insect species such as the poplar and willow borer, Cryptorhynchus lapathi (L.), were also originally of little concern. This Eurasian weevil was first recorded in BC in 1923, despite its reputation as a weak flyer, has doubled its range since 1964 and is now found as far north as Prince George and Bella Coola (Broberg, Borden &
Humble, 2002). With the advent of global warming and an increasing interest in poplar and willow for site reclamation and biomass production, this insect could become a significant economic pest. This prediction is supported by the discovery that the weevil is now killing mature black cottonwood, Populus balsamifera ssp trichocarpa (Torr. and Gray), in the Skeena
Valley of BC (K. White, oral report January 20, 2008). Both T. domesticum and X. politus come from similar habitats as C. lapathi and are also capable of attacking living trees, so it is expected that they will eventually cover the same range and may cause similar damage.
Lag times between introduction and population explosion are common. It took gypsy moth,
Lymantria dispar (L.), more than twenty years after their initial escape in Massachusetts in 1869 to become an observable pest (Krcmar-Nozic et al, 2000). Although the initial escape was reported, monitoring was not done and no effort was made to control the pest until an outbreak occurred. The attempts at eradication failed. Current efforts against gypsy moth throughout northeastern USA are concentrated on reducing its impact and slowing its spread.
While the lures used in this experiment caught some X. politus, the lack of a species-specific pheromone for this insect limits our ability to capture it in conventional trapping programs.
Currently, very limited trapping programs are used at ports to locate and capture beetle populations in green lumber bound for export. Trade restrictions, fumigation costs and increased Environmental Implications of Two Introduced Ambrosia Beetles 32 tariffs could result if X politus, living within export-bound lumber or logs, is not detected prior to its departure, but is subsequently discovered at a foreign port.
Unlike X. politus, which has been found in Washington and Oregon (Mudge et al., 2001), there are no collection records of T. domesticum south of the US/Canada border (J. R. LaBonte,
Oregon Department of Agriculture, personal communication, September, 2007). The apparent absence of this beetle from the USA could be used as a non-tariff barrier to the trade of hardwood forest products. Limitations could also come from other countries, e.g. Australia, that have rigorous phytosanitary restrictions.
The fungi associated with introduced insects could also create problems and affect the surrounding habitat. For example, in South Carolina and Georgia, extensive mortality of red bay,
Persea borbonia (L.) Spreng. caused by an anamorphic fungus (Raffaelea state of an undescribed
Ophiostoma sp.) has been traced back to its vector Xyleborus glabratus (Eichhoff), an introduced ambrosia beetle (Rabaglia and Fraedrich, 2007). There are four possibilities by which fungi associated with T. domesticum and X. politus could create an unexpected problem. It is possible that:
1. The fungi associated with T. domesticum and X. politus may prove to be pathogenic to
certain trees in BC that have not co-evolved with them. This question may be answered
when either species enters into the interior of BC and attacks trembling aspen, Populus
tremuloides Michx. Apparently healthy aspen are already attacked by the native
ambrosia beetle, T. retusum, which has apparently moved into a primary "tree killing"
role (Kiihnholz et al, 2001). Additional exposure to the fungi associated with introduced Environmental Implications of Two Introduced Ambrosia Beetles 33
beetles could be devastating. The pathogenicity of these fungi should be tested to
determine the possibility of this threat.
2. Isolated populations of the symbiotic fungi could mutate to a more virulent form like
Ophiostoma novo-ulmi Brasier, a highly aggressive new pathogen species of Dutch elm
disease fungus (Brasier, 2001).
3. Hybridization with native fungal species could also produce a new strain of pathogenic
fungus (Brasier, 2001).
4. A pathogenic fungus associated with a native bark or ambrosia beetle could be
transferred to T. domesticum or X. politus. For example, the native elm beetle
Hylurgopinus rufipes (Eichhoff), was not considered to be of economic importance in
North America (Humble & Allen, 2006), but it now carries Ophiostoma ulmi (Buisman)
Nannf. and O. novo-ulmi introduced to North America in the 1930's (Tisserat, 2006)
through the smaller European elm bark beetle, Scolytus multistriatus Marsham). Both
insects now spread the disease and have virtually eliminated elms from any area they
inhabit.
Fungal vectorship is of particular concern with X. politus, a species documented to have two species of primary ambrosial fungi (Ambrahamson & Norris, 1969). MacLean and Giese (1968) suggest that one of the species could be used as larval food, although neither its function nor its identification has been fully determined.
The United Nations Food and Agriculture Organization (FAO) has implemented a global standard for treating wood packaging material (FAO, 2006) which reduces the risk of future Environmental Implications of Two Introduced Ambrosia Beetles 34
introductions. However, "closing the door" to future problems may create a false sense of
complacency with regard to already introduced species currently not exhibiting worrisome
characteristics. As well, intra-continental movement is not addressed by this standard, so insects
could still move into new habitats via the movement of products across the continent as did
X. politus. Commercial transport of wood and wood products, changing forest practices and the
insects' ability to switch hosts may also open up pathways to new habitats. Ambrosia beetles are
the primary potential source of degrade in hardwoods (Allen, 1996), and should BC move further
into the hardwood market, T. domesticum and X. politus may become economically important
pests of unseasoned hardwood logs and lumber. The awareness that T. domesticum is now
known to attack weakened live trees (Henin et al., 2002; Kuhnholz et al., 2001) should reinforce
the necessity of continued monitoring. They could already be having a significant undetected
effect on urban trees.
Because ambrosia beetles invade the wood of trees, where defensive mechanisms are poorly
developed, and rely solely on their ambrosia fungi for food, they are well adapted to attack a wide
range of host species. For example, the native species G. retusus, which normally attacks
conifers, can successfully attack and produce brood in red alder ((Kuhnholz, Borden & Mcintosh,
2000).
Xyloterinus politus has already shown that it can successfully infest western hemlock (Henry,
2004), and it could potentially adopt other conifers as hosts. The high T. domesticum catches at
SFU shows how well the insect has adapted to red alder, a new host which is commercially
harvested in some areas of the province (Sunshine Coast, Campbell River, Chemainus). Its Environmental Implications of Two Introduced Ambrosia Beetles 35 apparent ease at switching to red alder, documentation on its ability to successfully attack big leaf maple (L. Humble, personal communication, January, 2008) and its wide range of hosts in
Europe, suggests it has a high potential of successfully switching to other hosts in BC, such as paper birch, trembling aspen and black cottonwood.
With a high percentage of deciduous forest cover, primarily red alder, Burnaby Mountain is well suited to T. domesticum. The threefold dominance of T. domesticum over T. lineatum at this site, as evidenced by trap catches, shows how quickly populations can build once a foothold is gained.
Trypodendron domesticum was also the predominant beetle at Port Mann during a 1999 survey for introduced scolytids (Humble, 2001).
The significantly higher T. lineatum catches in traps baited with ethanol plus lineatin over those with ethanol alone shows the importance of using specific pheromones (if available) in monitoring programs. While many Trypodendron spp. are attracted to lineatin ((Payne et al.,
1983; Kuhnholz, 2004), catches of T. retusum and T. rufitarsus in the ethanol plus lineatin-baited traps in the distribution study were not significantly higher than those in ethanol-baited traps.
Ethanol, produced by stressed, dying or dead trees is a primary attractant for many bark and ambrosia beetles (Graham, 1968; Kelsey, 1994), and it is possible that nearby natural host odors
(decaying hardwoods) may have provided X. politus and T. domesticum with an alternative odor source. Thus high catches for a given species may reflect population density and low catches establish presence, but zero catches do not necessarily indicate the absence of a species. Environmental Implications of Two Introduced Ambrosia Beetles 36
In the distribution study (but not the seasonal activity study), the higher catches of G. sulcatus in traps baited with lineatin and ethanol than in those baited with ethanol alone, approached significance (t = -1.6329, df = 44, P = 0.0548). This result supports Borden, et al. (1981), who found evidence of weak cross attraction of G. sulcatus to lineatin.
The early emergence of T. domesticum, both at SFU and the Malcolm Knapp Research Forest confirms data collected in Europe (Francke, 1973; Petercord, 2006), and its attraction to lineatin corroborates studies by Payne et al. (1983) and Kuhnholz (2004). While this attraction makes it possible to use current ambrosia beetle management programs to monitor for T. domesticum, traps will have to be set up and trap catches evaluated much earlier than the current March 15 deadline. This will provide an early indication of the spread of this species, and when catches are high, will allow differentiation of the species that are damaging to conifers from the one that is not. Trypodendron domesticum was caught during the first collection period in the third week of
February, when the maximum temperature reached only 12°C. These insects may have been flying even earlier, as recorded in Luxembourg and Germany. Petercord (2006) demonstrated a threshold flight temperature of 9.5°C for T. domesticum, while Francke (1973), in laboratory studies, recorded beetle emergence at 10.5°C. In the lower BC mainland and Vancouver Island these temperatures often occur in early February and sometimes even earlier
Trypodendron retusum and T. rufitarsus are prevalent in the BC interior where they are readily found in lineatin-baited traps. In southern BC, their emergence flights started when daily maximum temperatures reached 8°C (Kuhnholz et al., 2001), so when T. domesticum spreads into the interior, early season catches would include all three species, increasing the difficulty of Environmental Implications of Two Introduced Ambrosia Beetles 37 identification and estimation of the size of the pest population. Once T. lineatum begins to fly
(when temperatures hit 15.5°C) (Borden, 1988) identification difficulties will further intensify.
Additional expertise in the identification of scolytid beetles will be required, and pest managers will need appropriate training. Several operational mass-trapping programs are now managed by logging companies, with limited assistance from ambrosia beetle management consultants.
Counts of captured ambrosia beetles in these programs will become increasingly meaningless, unless they have access to taxonomic expertise. High catches could create unwarranted alarm until it can be determined which species are present and which are most abundant.
Xyloterinus politus catches were low at both SFU and the Malcolm Knapp Research Forest, although the latter site was specifically chosen as it was known to have an endemic population
(Henry, 2004). Higher mean temperatures, brought about by global warming would probably benefit X. politus as they prefer to fly at temperatures of 25°C or higher. If populations of
X. politus rise substantially, and they are captured in traps intended for other species, a mistaken impression of late-season threat to harvested timber could arise in the absence of taxonomic expertise.
Kiihnholz et al. (2001) hypothesized that angiosperm-infesting ambrosia beetles, such as
T. domesticum would gain an advantage if climatic warming occurs. Trees characteristically require an extended period of cold dormancy (vernalization) before metabolic activity can return to a high level in the spring. However, bud flush may be regulated at least in part by an increased photo-period. The beetles on the other hand are thermally-regulated (Fockler & Borden, 1972) once diapause is broken in early February. Prior to budflush, trees may respond to an early Environmental Implications of Two Introduced Ambrosia Beetles 38 spring rise in temperature by commencing anaerobic metabolism, thus producing ethanol as an attractant for early-emerging species like T. domesticum. Thus it may be necessary to shift the designation of ambrosia beetles from secondary beetles to primary beetles capable of successfully attacking apparently healthy trees. Trypodendron signatum and T. domesticum in Belgium
(Gregoire et al, 2002) and T. retusum (Kuhnholz et al. 2001) and T. domesticum (Humble, 2001) in BC all appear to be examples of such a shift.
My study has focused on two introduced ambrosia beetles. They are examples of the consequences of the increase in globalization, which is dramatically escalating the rate of invasion of introduced species. Experience shows that the most effective tools for invasive species management include: careful monitoring, expert taxonomic identification, rapid response, basic research, public outreach, meaningful restoration, sustained funding, industry co-operation and best management practices.
Recommendations
There are five recommendations that arise from my research.
Recommendation No. 1
Past experience with introduced species such as the poplar and willow borer, smaller European elm bark beetle, gypsy moth and many others has proven the importance of regular and continual monitoring for range expansion and population changes. Once an introduced species becomes established it is no longer the responsibility of the Canadian Food Inspection Agency, and responsibility for monitoring and management shifts to the provinces. I recommend that the Environmental Implications of Two Introduced Ambrosia Beetles 39
BC Ministry of Forests and Range implement an enduring monitoring program for introduced ambrosia beetles.
Recommendation No. 2
The new monitoring program should include: a) trapping for presence or absence, b) trapping to determine population levels, and c) surveying host material for new host-insect adaptations.
Recommendation No. 3
Introduced species are now a significant component of diversity in BC forests (Humble, 2001) but the presence of such insects throughout the country is largely unknown, despite the potential for intercontinental movement, as exemplified in X. politus. Therefore, I recommend that information on geographic range and population levels of introduced species be kept in a national data base, with consistent and regular updating. Range expansion and population increases can then be closely monitored, providing a base point should outbreaks occur.
Recommendation No. 4
Identifying and developing a species-specific pheromone for X. politus would increase the effectiveness of the monitoring program. I recommend that the BC Ministry of Forests and
Range ensure that research on identifying a pheromone for X. politus is implemented.
Recommendation No. 5
As the diversity of introduced scolytids increases, ambrosia beetle managers will require more comprehensive training. Many of these insects are impossible to identify to species with the Environmental Implications of Two Introduced Ambrosia Beetles 40 naked eye. Sub sampling of catches, with further identification in the laboratory, will be required. At this time, there are very few people that have the expertise to accomplish this.
Therefore, I recommend that the BC Ministry of Forests and Range commission an extension agency to offer (periodically as required) a short course on identification of ambrosia and other Scolytid beetles. Broadening the scope of such a course to include all
Scolytid beetles will ensure that the course will be of maximum use to a broad range of professionals. Environmental Implications of Two Introduced Ambrosia Beetles 41
References
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