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

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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.

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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

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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.

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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).

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Figure 2. Willow trees displaying symptoms of dying due to ALB attack

with withering leaves or dead branches

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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.

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Figure 5. The infested trees were felled for the experiments.

Figure 6. The stump shows ALB activity.

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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

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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).

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Figure 10. Small round exit holes in the logs.

Figure 11. The willow logs that will be treated.

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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

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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.

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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.

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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.

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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).

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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.

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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.

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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.

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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.

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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.

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Figure 26. The dead ALB larva from treated log after treatment.

Figure 27. More dead larvae found in the logs after treatment.

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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).

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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

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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

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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

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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.

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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

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Chen Z. and M. S. White. 2012. Development Of A Highly Efficient Steam And Vacuum

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31

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32

Appendix

More related photos were presented in this section.

Figure A1. The infested willow logs

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Figure A2. The infested willow log that will be vacuum/steam treated.

Figure A3. Trunk riddled with exit holes on the heavily infested logs.

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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