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1
Preliminary investigation of vacuum/steam treatment
of Asian long-horned beetles in naturally infested wood
Zhangjing Chen1, Marshall White
1 , Ron Mack
2
Ximing Wang3,
1 Research Scientist and Emeritus Professor, Virginia Tech, Blacksburg, VA 24060
2 Research Scientist, USDA, APHIS, PPQ
Pest Survey, Detection & Exclusion Laboratory
Bldg 1398, Otis ANGB, MA 02542
3 Professor, Inner Mongolia Agriculture University, China
July 20, 2012
Acknowledgments
Funding for this study was provided by US Department of Agriculture, Animal and Plant Health Inspection
Service and testing facilities were provided by Inner Mongolia Agriculture University. Hohhot, China. Special
thanks to Nanhai Park, Baotou city, China for allowing us to cut the ALB infested willow trees at its respective
properties.
2
Abstract
A study to control Asian long-horned beetles (ALB) Anoplophora glabripennis
(Motschulsky) (Coleoptera: Cerambycidae) in naturally infested logs with the vacuum/steam
technology were conducted at the Inner Mongolia Agriculture University, Hohhot City, Inner
Mongolia Autonomous Region, China. As an environmentally friendly alternative to chemical
treatment, this research focus on using vacuum and steam to treat ALB infested logs. The logs
cut from willow trees were obtained from the heavily infested area in the north China were
vacuum/steam treated at vacuum level 350 mmHg and steam temperature of 90C. The results
have shown that vacuum/steam treatment can kill the all ALB larvae in the naturally infested
wood in less than 500 minutes for diameter ranging from 10 to 26 cm at various initial
temperatures.
Introduction
Over 400 different insect species which feed on trees and shrubs have been introduced
into the U.S. primarily as a result of global cargo movement during the past 200 years (Hacck
2006). Asian longhorned beetles (ALB), Anoplophora glabripennis (Motschulsky) (Coleoptera:
Cerambycidae) and Agrilus planipennis (Coleoptera: Buprestidae) were introduced into the U.S.
from China in wood packaging material. ALB is the accidental introduction from China into
both North America (Fleming et. al. 2003) and Europe (Krehan 2002) during the early to mid-
1990s. In 1996, ALBs were discovered on hardwood trees in Brooklyn, New York. The beetle
infestation in New York has spread to Long Island, Queens, and Manhattan. In 1998, a separate
case of the beetle infestation was discovered on trees in the suburbs of Chicago, Illinois. Beetles
were also detected in New Jersey in 2004. In 2007, ALB was found on Staten and Prall’s Island
in New York.
A serious infestation was discovered in Worcester, MA. By late 2011, more than 30,000
trees were removed and chipped. Evidence indicates that the infestation may date back as far as
1997. Inspection of host trees within the 110 square mile quarantine area has revealed about
20,000 infested trees so far and that the ALBs are capable of moving into forest blocks. In 2010,
six infested trees were found in the Jamaica Plain neighborhood of Boston, MA, that is so close
to the Arnold Arboretum, the oldest arboretum in America. In 2011, another infestation of ALB
was found in the southwestern Ohio village of Bethel. Also, ALB has been detected on two
3
private properties in Stonelick Township in Clermont County in July, 2012 in Ohio (Agriculture
Department of Ohio State 2012). In addition, ALB has been discovered in southern Ontario,
Canada, and in France, Austria, Switzerland, Italy, and Germany. Alert workers have uncovered
and reported ALBs in warehouses in 15 states and several provinces of Canada (APHIS 2011).
ALB attacked the maples, chestnuts, poplars, willows, elms, mulberries and black locusts,
and a wide variety of hardwood trees in North America. ALB threatens urban and suburban
trees, as well as valued forest resources, and threatens such industries as maple syrup production,
hardwood lumber processing, nurseries and tourism. These trees represent many billions of
dollars to the U.S. economy by supplying lumber, wood products, maple syrup, and promoting
tourism.
ALB is a serious pest problem in China, where it causes significant economic loss in
poplar plantations. So far all ALB infestations in the US have been found in suburban and urban
environments. However, in the US where millions of acres of contiguous hardwood forests
occur, the impact of ALB is unknown but could be devastating. This country represents a new
environment for ALB with many different host tree species.
Quarantines have been established around infested areas to prevent accidental spread of
ALB. All infested trees have to be removed, chipped in place, and the chips are being
burned. The stumps of infested trees are ground to below the soil level. APHIS and its
cooperators undertake eradication by imposing quarantines, conducting visual inspections,
removing infested trees and chemically treating noninfested host trees as part of an integrated
eradication strategy.
The most widely used chemical fumigant has been methyl bromide (Gaunce et al. 1981,
Yokoyama et al. 1990, Moffit et al. 1992). In addition to preshipment and quarantine uses, Mebr
has been used extensively for phytosanitary treatments of food such as dried fruit, nuts, beans,
processed foods and pet foods, as well as the treatment of processing facilities. Another
chemical fumigant that has been studied is sulfuryl fluoride that was first registered as Vikane®
gas fumigant (Dow AgroSciences, Indianapolis, IN) in 1961 in the United States for treatment of
buildings, vehicles, construction materials, furnishings, and non-edible commodities for a variety
of pests (Thoms and Scheffrahn 1994, Barak et. al. 2010). However this gas has also been
labeled as potential green house gas.
4
Vacuum/steam can be an environmentally benign and effective alternative to chemical
fumigation for preshipment and quarantine treatment of wood packaging materials and wood
commodities. Vacuum can be used to lower pressure inside the wood. When steam is added,
the steam pressure is higher than the pressure inside the wood. According to Darcy’s law, vapor
is rapidly transferred due to a total pressure difference and the amount of moisture transferred is
directly proportional to the permeability. Water vapor condenses and changes into liquid water
during vacuum/steam treatment. Large amounts of heat are released to the wood and this rapidly
increases the temperatures of wood.
The vacuum/steam system can heat the wood and other substances fast. Preliminary
studies indicated the steam/vacuum treatment cycles are less than half those of current ISPM 15
HT hot air treatment methods and energy consumption is 25% less when treating the pallets
(Chen and White 2012). The system can be easily tailored to the different treating capacities.
The system can be designed as portable and transported easily from one location to another. The
technology can be adapted to the rigid or flexible container system. Heat treatment is an
environmentally benign. It is currently the most widely used treatment for compliance with the
ISPM 15 standard. The primary objective of this research project is determine the effectiveness
of the vacuum/steam treatment using the current Aphis standard of 60°C for 60 minutes for
killing the ALB larvae in logs cut from the ALB naturally infested trees. It is generally assumed
that 60 minutes at 60°C will kill ALB. The efficacy of the treatment will be demonstrated on
naturally infested wood. Wood naturally infested with the Chinese longhorned beetles is
available in China. Such efficacy research is best conducted in China.
Objective
The primary objective of this study is to demonstrate that a vacuum/steam treatment
using current APHIS treating standard of 60°C and 60 minutes can effectively eliminate the
ALBs in the logs sawn from the naturally infested trees that are available in Northern China.
Asian long horned beetles (ALB) life cycle
5
The ALB belongs to the family of wood boring beetles, Cerambycidae. ALBs have
characteristics in common with all beetle species, such as three major body sections: head, thorax
and abdomen. They have shiny black body with white spots and have six legs. The ALB has
four stages of life: egg, larva, pupa and adult. The ALB adults are 2.5 to 3 cm long (Figure 1).
Eggs are laid within the bark, and hatch in 1-2 weeks. Newly hatched larvae tunnel into the
vascular tissue of the tree. As they mature, larvae bore into the wood which causes extensive
damage. ALBs spend most of the year as larvae inside the tree. Larvae may reach 5 cm in length
when fully grown. At maturity, the larvae move near the surface of the tree (under the bark) to
pupate. Adults emerge in about 18 days. They have long antennae banded black and
white. Adult beetles are most active during the summer and early fall depending on the climate.
As adults, they often feed on the foliage of host trees. Asian longhorned beetle adult only lives
about 40 days. It takes a year to complete a life cycle for most part of China. The ALB chews
hardwood trees, particularly maple, birch, willow, poplar and elm. The larvae eventually kill the
tree. ALB kills young and mature trees by tunneling within the trunk and branches, disrupting
sap flow and weakening the tree. Because this beetle attacks many different tree species, it could
significantly disrupt the forest ecosystem, if it became established over a large area.
ALB infested trees
We have searched the ALB infested trees, such as, willows, poplars from several
locations in Northern China. We have found many seriously infested willow trees (Salix
matsudana) trees in the Nanhai park areas. The park was located in Baotou city, 120 kilometers
from Hohhot, the capital of Inner Mongolia Autonomous Region of China. Inner Mongolia is
located in the northern China. The winter usually is very long, cold, and dry with frequent
blizzards. Other seasons are short, hot, and have large sandstorms. Most of the region is
officially classified as a cold arid regime. Willow is an important scenery species planted widely
in parks and along the streets through whole China. Salix matsudana is a medium sized to large,
deciduous, upright, rapidly growing tree to 6 to 9 meters tall, but has a short lifespan.
6
Figure 1. Asian longhorned beetle adults.
In northern China, willow trees are more useful than just ornamental or habitat. They
also alleviate the movement of sand dust that has affected China and Korea. Recent years,
Korea was affected so much and it has also funded a tree-planting project in a Chinese desert to
reduce the amount of harmful "yellow dust" blowing over South Korea. The fund was used to
purchase and plant some 72,000 poplar and desert willow trees in Inner Mongolia's Kubuqi
Desert, 600 kilometres (370 miles) west of Beijing. The infested willow trees cut for this study
were about 30 kilometers from Kubuqi dessert. Kubuqi Desert, the world's seventh largest, is
blamed for causing 40 percent of "yellow dust" that blankets the Korean peninsula every spring.
When the tree were attacked by the ALB, growth is affected (Figure 2). Evidence of the
infestation is frass around the base of the tree or piled in the crotch of branches (Figure 3). The
adult beetle emerges from an oval exit hole. The large amounts of dust were found at the base of
tree from their exit holes when adults emerge from the tree (Figure 4). Infested willow trees
were harvested for treatment (Figure 5). The ALB activities can be seen at the stump (Figure 6).
The small logs were cut from the trees with length varying from 2 to 3 feet (Figure 7). A larva
can be seen at the log (Figure 8). The small branches of willow tree were not used (Figure 9).
7
Figure 2. Willow trees displaying symptoms of dying due to ALB attack
with withering leaves or dead branches
8
Figure 3. The frass from the larvae was found at the base of infested trees.
Figure 4. The large amount of dust was found at the base of tree.
9
Figure 5. The infested trees were felled for the experiments.
Figure 6. The stump shows ALB activity.
10
Figure 7. The willow logs were transported to Hohhot for vacuum/steam treatment
Figure 8. An live ALB larva can be seen when tree were cut
11
Figure 9. The willow leaves and branches from the cut willow trees.
Adult ALBs chew their way out of wood and leave exit holes in the trees (Figure 10). A
total of one hundred willow logs were used in this study (Figure 11). More photos about the
treated logs were presented in the appendix (Figure A1 to A6).
12
Figure 10. Small round exit holes in the logs.
Figure 11. The willow logs that will be treated.
13
Construction of the vacuum/steam treating system
A custom made flexible vacuum container was designed for this project. The system
consists of a liquid ring vacuum pump, flexible vacuum chamber, steam generator and steam
controller (Figure 12). Monitoring devices are used to record temperature within the flexible
container and the treated materials. The steam generator supplied the steam to the container.
The flexible vacuum container, made of woven fabrics, coated and impregnated with PVC
compounds, was used as the test chamber and its size 10 by 4 feet in the rectangular shape
(Figure 13).
Vacuum Pump
Flexible Container
Vacuum Gauge
Steam Supply
ALB infested logs
Figure 12. Schematic diagram of the vacuum/steam treating system
14
Figure 13. The flexible container used in the vacuum/steam treatment
Steam generator. A 75 KW steam generator is used to supply the steam (Figure 14). The
amount of steam supply was regulated with valve in order to control the temperature inside the
logs during the test. The steam temperature in this steam generator can reach 175 C at the
pressure of 0.8 Mpa. The capacity of the generator is 110 L, or about 30 gallons.
15
Figure 14. The steam generator used in the experiment.
Liquid ring vacuum pump with recirculation of ring liquid
Liquid ring vacuum pump (model 2BV2061) (Figure 15-16) was manufactured in China
and used in this study. The liquid ring vacuum pumps are the most used vacuum producing
devices in industry.
The pump is a rotary positive displacement pump utilizing liquid as the principal element
in gas compression. The compression is performed by a ring of liquid formed as a result of the
relative eccentricity between the pump casing and a rotating multi-bladed impeller. The
eccentricity results in near complete filling then partial emptying of each rotor chamber during
every revolution. The filing-and-emptying action creates a piston action within each set of rotor
of impeller blades.
The pump components are positioned to admit gas when the rotor chamber is emptying
the liquid, and then to allow the gas to discharge once compression is completed. Sealing areas
between the inlet and discharge ports are provided, to close the rotor areas, and to separate the
inlet and discharge flows. Single stage vacuum pumps typically produce vacuum to 35 mm Hg
or 47 mbar.
16
Figure 15. The liquid ring vacuum pump name plate.
17
Figure 16. Liquid ring vacuum pump and circulating water system used in the test.
Vacuum gauge.
The vacuum can be read from the vacuum gauge (Figure 17) installed in the vacuum line.
18
Figure 17. The vacuum gauge installed in the equipment.
Experimental procedure
After the green logs were transported to Inner Mongolia Agriculture University, they
were stored in the cooler to delay emerging of the adults under the warm temperature. The
cooler was set around the freezing point next to the treating room. To conduct the tests, logs that
are used in next test were taken out from cooler. The diameter and weight of logs were
measured. The moisture contents of the logs were also measured with oven-dry methods. Logs
were not debarked when tested. A hole roughly equivalent to the diameter of the temperature
probes was drilled to the depth of center of log. The temperature probe was then inserted into
the hole allowing us to accurately monitor the temperature of the center of log during every test.
At the same time, surface temperature and air temperature inside the container were measured
(Figure 18). The environment temperature also was recorded. At each test, four pieces of logs
were tested, three as test samples and one as control sample. The control sample was laid next to
the treating flexible container but not treated.
19
Figure 18. The connection of thermocouple to the flexible container.
Vacuum treatment was applied after the infested logs were inserted into the containers.
The flexible container then was zipped closed and vacuum was drawn to the test pressure inside
the container (Figure 19).
20
Figure 19. The zipper was used in the container for easy opening.
The test vacuum was set to 350 mmHg for all the tests. After the test pressure was
reached, the vacuum pump was stopped. Steam was then injected into the container so that the
temperatures inside the container and temperature at center of log increased. After the
temperature inside the chamber reached 80 ºC, steam injection was slowed to maintain the
temperature to less than 90ºC. When the temperature of center of logs reached 60°C then steam
was manually controlled to keep the center temperature at 60°C for 60 minutes. Then the
treatment cycle was considered complete. The container was open and logs were cooled down.
The weight of logs was measured after treatment (Figure 20). After the treatment, logs were split
to retrieve the larvae, pupae and adults (Figure 21). Axes and small hand saws were used to
carefully split the logs without damage to the ALB larvae, pupae and emerging adults (Figure
21). In order to get all the larvae out of wood, logs were chopped up into small stripes (Figure
22). The larvae were removed from the logs and maintained at room temperature (Figure 23).
After the tests, larvae (Figures 24 and 25) were considered dead if no movement was observed
within 3 hours of removal from treatment.
21
Figure 20. The balance used to weight the log samples before and after treatment
Figure 21. The hand saw and other hand tools used to split the logs.
22
Figure 22. The willow logs have to be chopped into small pieces
in order to search all the larvae.
Figure 23. The number of ALB larvae was recorded after logs were split.
23
Figure 24. Daily record of larvae, adult and pupae found in the control and treated
samples.
Figure 25. Dead ALB larvae and adults picked from the treated logs.
24
During the treatment, room temperature, vacuum, ambient temperature inside the
container and temperature at the surface of log and center of log were periodically recorded. To
accurately measure the temperatures during the test, we utilized thermocouples to measure the
temperatures.
Result and discussion
After the vacuum/steam treatment, the container was open and the treated logs were
removed. Each log was split to check whether the larvae were still alive in the test samples.
Lack of movement for three hours observation indicated death. All larvae, pupae and adult
inside the wood were dead (Figures 26 to 28 and more in Figures A7 to A10 in the appendix).
At the same time, the control samples were split and larvae were retrieved. Their movement was
observed and about 77% larvae were found to be alive. The number of larvae found in the
treated samples and control samples are in Table 1. Also the treatment duration for each test was
recorded and presented in the Table 1. A maximum of 500 minutes was required to treat the
logs for diameter ranging from 10 to 26 cm at various initial temperatures. This treatment time it
took is longer than treating pallets (Chen and White 2012). That is because pallet deck boards
and stringers are smaller than the logs. The vacuum/steam treatment time depends on the many
factors, the initial starting temperature, log diameter, the size of the heat source, species,
moisture content, and flexible container insulation.
The weight change of logs during the treatment was presented in Table 2. The initial MC
of log was measured to be 32.4% (ASTM 2007). From table 2, the weights of logs increased
after treatment and average MC increase was calculated to be 9.1% based on the data. MC
increase is related to the amount of energy needed to increase the temperature of logs and
compensate the heat loss.
25
Figure 26. The dead ALB larva from treated log after treatment.
Figure 27. More dead larvae found in the logs after treatment.
26
Figure 28. The dead adults were found inside the treated logs.
A typical temperature profile during the test was presented in the Figure 29. Ambient
temperature inside the container increased first and fast at the early treatment. It is followed by
the surface temperature. The temperature at the center of logs increased slowly. As expected, it
took longer to treat the larger logs (Figure 30).
27
Table 1. Larvae were found in the infested logs during the tests.
Test
Number of larvae
found in Treated logs
(All dead)
Number of
larvae found in
control log
Treatment time
Including
holding time
(min)
Initial
temperature
Of log
(°C)
Small end
Diameter
(mm)
1 15 3 7 6 510 -3
2 13 18 14 5 300 20.2
3 23 0 1 12 285 21.8
4 40 6 1 0 225 20.2
5 8 14 2 6 236 20
6 0 14 7 10 186 19.5
7 12 9 17 176 24.6
8 14 7 4 270 22.1
9 0 4 1 240 22.5 200
10 2 5 7 292 10.8 230
11 7 17 10 182 7.4 200
12 7 10 3 205 16.5 225
13 11 2 2 442 15.9 260
14 10 9 3 225 19.5 190
15 9 1 0 270 17.6 250
16 6 19 15 355 16.5 220
17 1 1 1 366 17.4 225
18 6 3 1 235 16.5 210
19 3 7 1 153 23.7 140
20 3 3 10 315 25.8 238
28
Table 2. The weight of logs before and after the treatment
Test Testing logs Control
log
1 1 2 2 3 3 4
Weight
before
treatment
(kg)
Weight
after
treatment
(kg)
MC
Gain
(%)
Weight
before
treatment
(kg)
Weight
after
treatment
(kg)
MC
Gain
(%)
Weight
before
treatment
(kg)
Weight
after
treatment
(kg)
MC
Gain
(%)
1 15.25 16.55
11.3 7.6 8.3 12.2
8.7 10 19.8
10.2
2 7.2 8 14.7 6.9 7.5 11.5 4.1 4.5
12.9 7.9
3 14.8 15.8 8.9 17.8 19 8.9 2.8 3.0
9.5 7.2
4 9.2 9.7 7.2 3.0 3.2 8.8 1.8 1.9
7.4 1.5
5 8.8 9.5 10.5 3.0 3.3 13.2 1.9 2.1
13.9 3.45
6 8.7 9.2 7.6 5.1 5.5 10.4 1.3 1.4
10.2 1.2
7 7.2 7.6 7.4 8 8.6 9.9 6.7
8 12.8 13.2 4.1 5.8 6 4.6 10.6
9 10.3 10.8 6.4 12.0 12.6 6.6 12.65
10 16.4 17.5 8.9 15.5 16.5 8.5 19.5
11 8.4 8.8 6.3 9.0 9.6 8.8 6.0
12 13 13.8 8.1 13.8 14.5 6.7 8.8
13 20.9 22.2 8.2 16.6 17.6 8.0 17.1
14 9.8 10.8 13.5 9.0 9.9 13.2 9.1
15 15.7 16.6 7.6 15.6 16.2 5.1 17.1
16 13.1 13.9 8.1 18.2 19.3 8.0 17.9
17 10.6 10.9 3.7 8.40 8.8 6.3 8.6
18 13.5 14.2 6.9 10.4 11.0 7.6 10.7
19 8.3 8.9 9.6 6.6 7.2 12.0 10.8
20 14.9 15.8 8.0 15.8 16.7 7.5 15.4
Average MC
Gain (%) 9.1
29
Figure 29. A typical temperature profile of vacuum steam treatment
of a 22.5 cm diameter willow log
0.0
20.0
40.0
60.0
80.0
100.0
0 100 200 300 400
Tem
pera
ture
(C
)
Treating time (min)
Log center Log surface Chamber
30
Figure 30. The relationship between vacuum steam treatment time and the diameter of logs.
Conclusion and recommendation
The study has demonstrated that vacuum/steam treatment can kill the all ALBs in the
naturally infested 10 to 26 cm diameter logs in less than 500 minutes. The temperature of 60°C
and for 60 minutes at the center of the logs is adequate to kill all ALB larvae, pupae, and adult
beetles present. Our study also suggests that the flexible container vacuum/steam system is
suitable to heat treatment in the field and can be a cost-effective treatment system.
Literature Cited
Agriculture Department of Ohio State. 2012.
http://www.agri.ohio.gov/public_docs/news/2012/07.20.12%20ALB%20Stonelick%20T
ownship20Discovery%20Announcement.pdf.
APHIS. 2011. http://www.aphis.usda.gov/plant_health/plant_pest_info/asian_lhb/index.shtml.
ASTM. 2007. Standard test methods for direct moisture content measurement of wood and
wood-base materials. Standard D 4442. West Conshohocken, PA: ASTM International.
Chen Z. and M. S. White. 2012. Development Of A Highly Efficient Steam And Vacuum
Phytosanitation Treatment For Solid Wood Packaging Materials. Report submitted to
Wood Education and Resource Center, US Forest Service, Princeton, WV. 53pp.
http://www.agri.ohio.gov/public_docs/news/2012/07.20.12%20ALB%20Stonelick%20Township20Discovery%20Announcement.pdfhttp://www.agri.ohio.gov/public_docs/news/2012/07.20.12%20ALB%20Stonelick%20Township20Discovery%20Announcement.pdfhttp://www.aphis.usda.gov/plant_health/plant_pest_info/asian_lhb/index.shtml
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Agrawal, V.C. Mastro, D.R. Lance, J. E. Shield, and R. Roy. (2003). Microwave
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Krehan, H. 2002. Asian longhorned beetle in Austria: Critical comments on phytosanitary
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32
Appendix
More related photos were presented in this section.
Figure A1. The infested willow logs
33
Figure A2. The infested willow log that will be vacuum/steam treated.
Figure A3. Trunk riddled with exit holes on the heavily infested logs.
34
Figure A4. Large end of treated logs.
Figure A5. The sizes of the infested logs were measured in its diameter.
35
Figure A6. The infested logs were labeled and numbered.
36
Figure A7. ALB adult was dead from the treatment
37
Figure A8. The several dead larvae could be found in a single test
38
Figure A9. Both larvae and pupae were found in the treated logs.
Figure A10. Many larvae were found in the treated logs.
39