Evaluation of vacuum technology to kill larvae of the Asian longhorned beetle, Anoplophora glabripennis (Coleoptera: Cerambycida

The potential for using vacuum technology to kill larvae of the Asian longhorned beetle (ALB), Anoplophora glabripennis (Motschulsky) (Coleoptera: Cerambycidae), and emerald ash borer (EAB), Agrilusplanipennis Fairmaire (Coleoptera: Buprestidae), in solid-wood packing materials (SWPM) and other wood products was assessed. Current regulations require that SWPM be heat treated or fumigated prior to export. Vacuum treatment may be a cost-effective and an energy-efficient alternative that eliminates environmental concerns associated with chemicals used in fumigation. Low pressure, achieved by applying a vacuum to a system, imposes a controlled atmosphere and desiccating environment that results in death of wood-infesting insects. Larval ALB and EAB, either exposed directly to vacuum or inserted into wood at various moisture levels, were subjected to different temperatures and pressures to determine desiccation rates and lethal percentage weight loss. Some ALB and EAB larvae died at 26 percent weight loss, and all were dead at 40 percent weight loss. Desiccation under low-pressure vacuum also killed ALB pupae and eggs. The desiccation rates of both ALB and EAB larvae under vacuum were constant until death, but decreased as larvae approached complete desiccation (approximately 60 percent weight loss). ALB larvae lost weight faster than EAB larvae at 20 mmHg and 20[degrees]C (3.35% weight loss per hour and 2.39 percent, respectively). Lethal vacuum time at 40 percent weight loss was estimated to be 13.2 hours and 18.5 hours, respectively, for exposed ALB and EAB larvae treated at 20 mmHg and 20[degrees]C. Under the same vacuum conditions, lethal time was estimated to be approximately 51.4 hours and 44.8 hours, respectively for ALB and EAB inserted into wood blocks with 16.6 to 21.6 percent moisture content. Temperature, pressure, and relative humidity affected desiccation rate. Larvae desiccated slower with decreasing temperature, increasing pressure, and increasing internal wood moisture.

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Wood-packing materials such as pallets and crating made of unprocessed wood can be infested with insects and other organisms (Haack 2006). The spread of pests in solid-wood packaging material (SWPM) can significantly alter ecosystems, hurt regional economies, result in significant remediation costs and limit the international flow of goods (Mumford 2002). The Asian longhorned beetle (ALB), Anoplophora glabripennis (Motschulsky) (Coleoptera: Cerambycidae), is an example of such a pest. ALB, a serious tree pest in China (Haack et al. 1997), has been intercepted in warehouses in at least 14 states in the United States (USDA APHIS 2007). ALB poses a threat to American hardwood forests because of its wide host range and its ability to attack and kill apparently healthy trees. It attacks members of the genera Acer, Aesculus, Betula, Fraxinus, Populus, Salix, and Ulmus (Haack et al. 1997). In the United States, eradication programs have been implemented in Illinois, New York, and New Jersey to prevent the enormous losses that could occur should this beetle thrive and spread unchecked. ALB infestations have the potential to eliminate up to 35 percent of the current canopy cover in North America (1.2 billion trees), with losses of $669 billion (Nowak et al. 2001). Eradication programs have resulted in the removal of thousands of trees at a cost of millions of dollars (Markham 2004).

The emerald ash borer (EAB), Agrilus planipennis Fairmaire (Coleoptera: Buprestidae), is another exotic beetle now present in the United States that probably arrived in SWPM. It is native to Asia and was discovered in southeastern Michigan near Detroit in the summer of 2002 (Haack et al. 2002). The larvae feed on the inner bark of ash trees (Fraxinus sp), disrupting the tree's ability to transport water and nutrients. As of 2006, EAB had killed at least 15 million ash trees in Michigan, Ohio, and Indiana (Poland and McCullough 2006). Unless effective control measures are developed and implemented, EAB could threaten the ash resource nationwide. Both ALB and EAB are of particular concern because they attack and kill apparently healthy trees. Methods to prevent reintroduction of these pests and introductions of other potential pests in SWPM are needed.

An international standard was adopted by the International Plant Protection Convention (IPPC) in 2002 that requires SWPM to be treated with a gas fumigant (methyl bromide) or with heat that achieves a minimum core temperature of 56[degrees]C for 30 minutes (FAO 2002). This Intemational Standard for Phytosanitary Measures was published as Food and Agricultural Organization Publication 15 and is commonly known as ISPM-15. This standard is now being adopted as a regulation by individual countries, including the United States (USDA APHIS 2004). As of 2005, methyl bromide is prohibited for use in developed countries for all purposes except quarantine and preshipment treatment as part of the United Nations Environment Program (1998). Heat treatment is costly due to its high energy input requirements. Thus, there is a need for globally-acceptable treatment alternatives that provide assurance of eliminating the risk of infested wood materials while being cost-effective and environmentally benign. Vacuum treatment may present an economical and energy-efficient alternative (Sattho and Yamsaengsung 2005) that does not release ozone-depleting chemicals or other pollutants, and does not affect the appearance or properties of the wood (Lee and Harris 1984, Harris and Taras 1985). Previous research (Chen et al. 2007) has demonstrated the commercial feasibility of using low-pressure vacuum technology to kill other small species of longhorned beetles (Monochamus and Stenocorus spp.) and the pinewood nematode (Bursaphelenchus xylophilus (Steiner & Buhrer) Nickle). The invertebrates die due to desiccation under low-pressure vacuum. Water loss in insects occurs via cuticular transpiration, respiration, secretion from mouth and anus, and via excretion (Hadley 1994). Since larger individuals have a greater initial water mass and higher volume to surface area ratio, which both contribute to longer survival under desiccating conditions (Renault and Coray 2004); we needed to evaluate this method with larger larvae of a species that can be transported in SWPM.

The objective of this research was to evaluate the effectiveness of vacuum treatment against ALB and EAB larvae. Our specific objectives were to determine 1) the lethal time of treatment for mortality of larvae, 2) the lethal percentage weight loss of larvae, 3) the desiccation rate of larvae, 4) the relationship between vacuum time and weight loss of larvae, 5) the relation between desiccation rate and wood moisture content (MC), and 6) the effects of temperature, pressure, and relative humidity on the desiccation rate.

[FIGURE 1 OMITTED]

Materials

Vacuum treatment equipment

The equipment used consisted of a vacuum pump, condensing system, vacuum control system, vacuum oven, and a balance (Fig. 1). A VacTorr vacuum pump by GCA/Precision Scientific (Winchester, Virginia) was used in these experiments. The vacuum capacity was 1 mmHg. Due to its sensitivity to moisture vapor, a condensing system was added to trap vapor released from the desiccating wood and larvae. A Neslab air-cooled CC-65 condenser was used and consisted of a mechanical refrigeration system that employed a single stage with one compressor. It had a temperature range of -20 to -55[degrees]C and the capacity to remove 120 W of heat at -20[degrees]C. The cold trap was used to condense and collect water vapor from the wood and larvae. The balance used in the experiments had a capacity of 60 g maximum weight with 0.1 mg precision and had a built-in RS-232 interface, which was used to transfer weight data every 5 seconds directly to a computer via a data acquisition system.

Vacuum pressure was controlled between [+ or -]2 mmHg by a HPM -760 Plus Controller (Teledyne and Hastings Co., Hampton, Virginia), vacuum gauge combined with a solenoid valve. Humidity and temperature were measured with a THT-I Electronics relative humidity meter equipped with humidity and temperature sensors (Shinyei Corporation of America, New York). The humidity meter was capable of measuring relative humidity (RH) from 0 to 100 percent with 1.5 percent accuracy over a wide temperature range (-50 to 200[degrees]C) in a vacuum. A Sheldon 1425 vacuum oven was used in the studies (Sheldon Manufacturing, Cornelius, Oregon). The vacuum oven had a stainless steel chamber and could regulate the temperature from 10[degrees]C above ambient to 240[degrees]C.

Supply of insects

Anoplophora glabripennis larvae used in the experiments were reared in the USDA Forest Service quarantine laboratory, Ansonia, Connecticut, according to procedures described in Keena (2005). ALB larval weight ranged from 0.5 to 2.5 g and about half(the heavier ones) were in their ultimate instar but had not received any chill. EAB larvae were excised from infested logs. Ash trees (Fraxinus spp.) infested with overwintering EAB were felled at field sites near Ann Arbor, Michigan, between January and March 2006 and cut into 60-cm-long log sections. Logs were held in a cold room (5 [+ or -] 2 [degrees]C) for up to 4 months until dissection. Logs were dissected in the USDA Forest Service laboratory in East Lansing, Michigan. Excised larvae were held in a refrigerator (5 [+ or -] 2[degrees]C) for up to 48 hours before treatment. EAB larval weight ranged from 0.05 to 0.13 g. Most EAB larvae were in their ultimate instar and near pupation.

Methods

Effectiveness of vacuum treatment and lethal percentage weight loss of larvae

A total of 32 ALB and 75 EAB larvae were held from 6 to 24 hours under 20 mmHg vacuum at 20[degrees]C to determine lethal percentage weight loss, lethal time, and the relationship between the two. Up to 10 ALB or EAB larvae were placed in the vacuum oven at one time. One larva was placed on the load cell and its weight was recorded every 5 seconds using data acquisition software. All larvae were weighed before and after treatment in order to calculate individual weight loss and desiccation rate.