Evaluation of Copper Ethanolamine Boron Based Wood Preservative to Control Wood Destroying Insects  

Aparna Kalawate
Biology Division,Indian Plywood Industries Research and Training Institute, P.B.No 2273, Tumkur road, Bangalore-560 022, (India)
Author    Correspondence author
Molecular Entomology, 2013, Vol. 4, No. 2   doi: 10.5376/me.2013.04.0002
Received: 24 Jan., 2013    Accepted: 29 Jan., 2013    Published: 14 Mar., 2013
© 2013 BioPublisher Publishing Platform
This is an open access article published under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Preferred citation for this article:

Aparna Kalawate, 2013, Evaluation of Copper Ethanolamine Boron Based Wood Preservative to Control Wood Destroying Insects, Molecular Entomology, Vol.4, No. 2 6-12 (doi: 10.5376/me.2013.04.0002)

Abstract

In the present study, efficacy of Copper-Ethanolamine-Boron (CEB) against powder post beetle and subterranean termite has been evaluated. The methodology adopted for the treatment of solid wood was by way of dipping and for plywood by glue line poisoning. CEB (10% w/v) was tested at various concentration levels viz., 2.5%, 3% and 5% against wood destroying insects. From the results of the toxicity study, it has been found that the lethal dose of CEB to control the attack of powder post beetle and subterranean termite was 2.5% in both the methods. In India, this is the first report of replacing chromium with Ethanolamine to fix the Copper and Boron in wood to control the wood destroying insects.

Keywords
Copper; Ethanolamine; Boron; Powder post beetle; Subterranean termite; Wood protection

Introduction
Products manufactured from plantation timber species are susceptible to the attack of wood destroying insects. This can be easily avoided by giving proper preservative chemical treatment. There are two main types of insects which attacks on wood and wood based panel products i.e. powder post beetle (PPB) and subterranean termite.

Powder post beetles are major pests found in sawmills, timber yards, factory premises, warehouses, where hard wood products like planks, boards, veneers or plywood are stored awaiting further processing. The common borers found in such situations are Lyctus spp. or Minthea spp., which have a worldwide distribution. Lyctus spp./Minthea spp. infestation is easily recognized by the flight holes in timber and panel material along with abundant frass (powder) which is tightly packed into the tunnels and forms little heaps beneath or around the flight holes. The flight holes are round with no staining around their margins and about 1.5mm to 3.0 mm diameters depending on the species. Initial attack by powder post beetle is hard to detect and is generally overlooked until attack is much advanced.

Termite infestation is a serious problem in many tropical countries (Lee et al., 2003). Wood cellulose is the principal food of the termites. They attack on both the live and dead woody matter. The damage by them is undoubtedly enormous and on an average the common loss is 10% to 30% (Remadevi and Muthukrishnan, 2004). Termite damage to historical buildings is both costly, irreversible and diminishes the integrity of a structure (Su et al., 1998). Subterranean termites are considered as one of the most economically important pests in the world (Perrott, 2003). In addition they are the most destructive and economically important insect pest of wood and other cellulose products and are responsible for 80% of all termite damage (Su and Scheffrahn, 1990). Subterranean termites need moisture from the soil but they have the ability to carry moisture in the buildings. They build characteristic shelter tubes made up of mud, wood fragments and bodily secretions by which they move from soil to wood above ground without exposure to drying air or predator.

Protection of wood from termite damage has always been a challenge as no method except the use of highly durable wood species or pre-treatment of wood with appropriate wood preservative offers a satisfactory, cost effective and long term protection from termites (Satish Kumar, 1995). The conventional proprietary wood preservatives such as CCA (Copper chrome Arsenic), CCB (Copper Chrome Boron) etc. are under scrutiny due to environmental reasons (Onuorah, 2000). When CCA-treated wood is removed from service its disposal can cause serious environmental problems because it retains high levels of toxic elements (Sye Hee Ahna, 2010). Humar et al. (2004) predicted that the volume of the CCA-treated waste wood would be 16 mm3 in 2020.

Copper and Boron based wood preservatives have an important drawback like leaching out from the treated wood. Soluble metal salts could be made insoluble or fixed inside wood by addition of chromium. Due to the carcinogenic nature of chromium compounds most of the European countries intend to ban the use of chromium in wood preservatives. Some of them will allow use of chromium preserved wood only for special purposes that are classified as hazard class IV. Use of chromium based wood preservatives will be banned in future for children playground equipment and garden furniture. Therefore, intense research is going on in the world laboratories to develop environmentally acceptable solution to fix Copper and Boron in wood.

Chromium based preservatives are under constant review due to environmental reasons and these formulations face threat to be phased out in the future (Tripathi et. al., 2005). On perusal of literature, it has been found that the work on Copper Ethanolamine Boron (CEB) based preservatives has not been done in India and hence in the present study an attempt has been made to evaluate the bioefficacy of CEB against PPB and subterranean termite.

1 Result
Results of toxicity test for PPB covering exposure periods of 6, 12, 18 and 30 months are presented in Table 1 (Figure 1). The results of borer tests indicated that borer holes appeared within six months of exposure in the untreated control samples. CEB chemical at all tested concentrations proved to be significantly superior in arresting the attack of power post beetle. The samples treated with CEB at the lowest concentration level of 2.5% resisted the attack from Lyctus africanus. In CEB at all the tested concentration level the samples were free of attack from Lyctus africanus until the end of the study i.e. thirty months. Hence, based on results of the toxicity study the lethal dose to kill the powder post beetle in the present investigation was found to be 2.5%.
 
 

Table 1 Toxicity of preservative treated plywood against Powder post beetle

  

 

Figure 1 Plywood samples after exposure study against Powder post beetle


Table 2 shows the mean absorption value of different treatments of CEB (Test yard specimens). Minimum absorption of 2.39 kg/m3 of CEB was found at CEB 2.5% concentration level. Rate of absorption increased with the increase in concentration of CEB. Absorption was maximum (3.36 kg/m3) at 5% concentration level. 3.28 kg/m3 of absorption was found in CEB at 3% concentration.
 

 

Table 2 Absorption of CEB (10% w/v) in veneer and solid wood of rubber wood


Table 3 shows the percentage of damage by subterranean termite in treated and untreated solid wood samples exposed in the test yard. Observations were taken periodically for a period of 6, 12, 24 and 30 months. The untreated control samples were damaged up to 50% within 12 months and nearly 92% within 30 months of exposure. It can be seen from the Figure 2 that treated samples are almost sound upto 24 months of exposure at all the treated concentrations. CEB at 5% concentration level resulted as the best treatment in arresting the attack of subterranean termite. Even at the end of the study, CEB at 2.5% and 3% concentration shows slight damage of 4% and 3.11% respectively. At the end of the test i.e. after 30 months, the treated solid wood samples recorded the attack in the range of 2 to 4 average percent attack which is rated as trace attack as per IS 4833 (Anonymous, 1993). 

 

 

Table 3 Efficacy of CEB against subterranean termite on solid wood

  

 

Figure 2 Solid wood samples after exposure study against subterranean termite


In case of glue line poison treated plywood samples, the untreated panels were damaged up to 89.84% within twelve months and 100% in 24 months of exposure (Table 5 and Figure 3). Whereas, the panels treated with CEB at all concentrations i.e. 2.5%, 3.0% and 5.0% resisted the attack till 24 months. At the end of the study period, lowest studied concentration rate of 2.5% showed trace average attack of 4.91%. CEB at 3% concentration rate also recorded the trace attack (4.22%). 3.41% of attack was recorded in 5% concentration. 

 

 

Table 5 Efficacy of CEB against subterranean termite on Plywood

  

 

Figure 3 Plywood samples after exposure study against subterranean termite


The results of both the test viz., solid wood and plywood against subterranean termites were subjected for Analysis of Variance (ANOVA) (Table 4 and 6). From the ANOVA it was found that there is a significant difference between the concentration of CEB and the attack of subterranean termite on solid wood and plywood. The attack of subterranean termite decreases as the increase in concentration of CEB chemical in both the solid wood and plywood. 

 

 

Table 4 ANOVA

 

 

Table 6 ANOVA


2 Discussion
Rubber wood is prone to attack by PPB and subterranean termite. New generation pesticides are effective at very low usage rate. Hence, the present study was designed to explore how different doses of CEB affect the durability of rubber wood against PPB and subterranean termite. 

Preservation of wood has been considered to increase the life of wood 5 to 8 times. Many formulations like CCA, CCB, ACC (Acid Copper Chrome), BCCA (Boron Copper Chrome Arsenic) contains Copper, Arsenic, Boron, etc., either individually or as a mixture using Chromium as a fixative agent are being used worldwide. The use of Arsenic and Chromium based compositions are under constant review for environmental reasons and these formulations face the threat of being phased out in the future. Hence, before it will be phased out an alternate wood preservative chemical has to be found out. Moving in this direction an attempt has been made in the present study to assess the bioefficacy of CEB against PPB and subterranean termite.

The absorption of preservative chemical was found in the range of 2.39 kg/m3 to 3.36 kg/m3 in half an hour dipping. This may be due to the reason that Rubber wood is highly permeable in nature and hence absorption of preservative was found to be adequate.

The most important criteria for judging performance of a newly developed preservative system is the field efficacy tests. Hence, in the present investigation the field efficacy test was performed to assess the performance of CEB in actual service condition.

CEB (10% w/v) at 2.5% was proved to be the best insecticide in this study. No doubt, that the highest tested concentration of CEB at 5% was excellent in controlling PPB and subterranean termite. But on the background of better bioefficacy obtained at the lower dose of CEB 2.5%, its use would be relatively safe to the workers and the end users. Hence, CEB at 2.5% has been recommended as the lethal dose to control the wood destroying insects. The insecticidal property of Boron is widely proven and in the present study the Boron has been fixed in the treated wood and this may be the reason for the excellent activity of the CEB chemical against PPB and subterranean termite. Borates like boric acid, borax or disodium octaborate tetrahydrate have proved their efficacy as wood preservatives for many years. The insecticidal properties of CEB found in this study may be due the presence of Boron. These are in consistent with Su and Scheffrahn, 1991 and Ahmed et al., 2004. These compounds have shown to be highly toxic to insects including termites, and fungi (Lloyd, 1997; Drysdale, 1994).

Copper sulphate and Boric acid have multi spectrum biocide activity but none of them have efficient fixation capacity in wood. Thus, present formulation has an advantage that an appreciable amount of individual metal ion could be fixed. Efficient protection of rubber wood at all concentrations was achieved against PPB and subterranean termite. On the basis of results and discussion of present investigation it can be concluded that CEB (10% w/v) at 2.5% may be adopted as the lethal dose to control PPB and subterranean termite.

3 Materials and Methods
The experiments were conducted during 2009 to 2012. The laboratory and field experiments were conducted at laboratory and test yard of Indian Plywood Industries Research&Training Institute (IPIRTI), Bangalore, Karnataka respectively. The experiment to evaluate the efficacy of CEB against PPB and subterranean termite was as per IS 4873 (Part 2) (Anonymous, 2008) and IS 401 (Anonymous, 2001) respectively.

3.1 Wood specimens
Specimens were made of Rubber wood (Hevea brasiliensis). Rubber wood has a density of 560~640 kg/m3 (16% M.C.). Seasoned rubber wood is being used for making furniture in India. It comes under non-durable class of timber as per IS: 401 (Anonymous, 2001). The samples selected for the study were free from visual defects.

3.2 Treatment solutions
CEB composition consisted of Copper sulphate, Mononethanolamine (MEA), Boric acid, Octanoic acid and co-biocide based aqueous solution. The stalk solution of CEB (10% w/v) was made by mixing Copper sulphate, MEA, Boric acid, Octanoic acid/Caprylic acid and Propiconazole in tap water. The molar ratio of the mentioned chemicals was kept as follow:

Ethanolamine: Octanoic acid: Copper sulphate: Boric acid: Propiconazole=1:0.083 8:0.223:0.158:0.0045

The above mentioned chemicals were mixed in tap water to make solution. The chemicals were added in the water (stock solution) as shown below in Figure 4.
 

 

Figure 4 Flow chart to make CEB solution


The pH of the CEB solution was 10 at the time of preparation and did not change even after one month of storage in the laboratory.

3.3 Treatment of Solid wood planks by dipping method
Solid wood of rubber wood was treated with CEB (10% w/v) by dipping method for half an hour. The concentrations used for the treatment were 2.5%, 3% and 5% made from the stalk solution. The moisture content of the wood before dipping was in the range of 25~30%. The samples were of size 30 cm × 30 cm × 2.5 cm. After getting maximum absorption in 30 minutes the planks were removed. The blocks were blotted off to remove free liquid and were reweighed. The percentage of intake of preservative or the amount of preservative absorbed by the sample was calculated in kg/m3 as per IS 4873 (Anonymous, 2008). The samples were conditioned and subjected in the test yard to assess the bioefficacy of CEB against subterranean termite. 

3.4 Glue line treatment of plywood
Three concentration levels viz., 2.5, 3 and 5% of CEB respectively were mixed with PF resin as glue additive on the weight of solid content of resin. Control samples were also prepared in which preservative chemical was not added in glue. The veneers were dried to a moisture content of 6~8% and then coated with above adhesive mixed. The glue coated veneer were given an open assembly time of 1.5 to 2 hours to attain moisture content of 12~14%.

The veneers were then assembled to 4 mm thickness and loaded into the hot press. The assembly was hot pressed at a temperature of 145 ± 5℃ with a specific pressure of 14~16 kgs/cm2. Curing time of thickness + 3 minutes was provided. The hot pressed panel was downloaded and stacked for about 24~48 hours for stabilisation. The panels were then dimensioned to required size for further evaluation.

3.5 Toxicity of CEB against Lyctus
The toxicity test was carried out as per IS 4873 (Part 2) (Anonymous, 2008). Adults of the powder post beetle i.e. Lyctus africanus were used for the test which were obtained from the laboratory cultures. Toxicity test Plywood made from Rubber wood veneers were cut into test samples of 10 cm × 4 cm size. Six replications were used in each treatment. The treated along with untreated control samples were kept with material infested with powder post beetles (Lyctus africanus) in culture tubs. Monthly observations were made and recorded as IS 4873 (Part 2) (Anonymous, 2008), covering a total exposure period of eighteen months. Results are presented in Table 1. Photographs of plywood samples after exposure of thirty months are depicted in Figure 1.

3.6 Field test/ test yard/ grave yard test
Toxicity test was performed according to IS 4833 (Anonymous, 1993). Treated and untreated solid wood and plywood samples were randomly installed in test yard. Six replications were made for each treatment with control stakes in rows at test yard. Termite activity and percentage of damage to the test panels were recorded at the intervals of three months. Observations were made covering a total exposure period of thirty months. Specimens were reinstalled in their respective positions after each inspection. The knife test or sound test was carried out as and when necessary to determine the extent of decay or destruction due to termite attack till the sample was destroyed. The visual observations and ratings were done according to the IS 4833 (Anonymous, 1993). Results of toxicity studies on CEB against subterranean termite on solid wood and plywood against termites are presented in Table 3 and Table 5 respectively.

Author’s Contribution
The new chemical has been developed by the author. Bioefficacy study, statistical analysis and manuscript preparation has also been done by the author.

Acknowledgement
This paper is published with kind permission of Director, IPIRTI, Bangalore, Karnataka, India.

References
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