EFFICIENCY OF NATURAL WOOD EXTRACTIVES AS WOOD PRESERVATIVES AGAINST TERMITE ATTACK

Wood extractives play a major role in the protection of wood against termite and fungal attack. Wood extractives from three hard wood species of Milicia excelsa, Albizia coriaria and Markhamia lutea that are known to be very resistant against termite attack and fungal decay were studied to assess their role as wood preservatives in Uganda. Acetone, hexane and distilled water were used in the extraction of these compounds from the outer heartwood of the selected durable species. Extraction was done using a soxhlet extractor. e extractives obtained were used to treat Pinus caribaea and Antiaris toxicaria species known to be susceptible to termites and fungal attack. Treated blocks were then exposed to Macrotermes bellicosus termites in the eld. It was observed that wood extracts used as preservatives improved the resistance of less durable samples to termite attack by 50% compared to the controls. It was also observed that removal of extractives decreased resistance of the durable samples. It can be concluded that wood extractives contribute greatly to the protection of less durable wood species against termite attack.


INTRODUCTION
Wood being a biological material is readily degraded by bacteria, fungi and termites (Walker 1993, Schultz andNicholas 2002).However, some wood species are resistant to these degrading agents while others are very susceptible to deterioration (Kityo and Plumptre 1997).Wood preservation is a process of reducing and/or preventing attack by wood deteriorating agents thereby increasing the service life of wood (Barnes 1992).
At present, most wood is treated with synthetic organic and inorganic substances such as Copper Chromium Arsenate (CCA) and creosote.ese synthetic chemicals are expensive and o en harmful to the workers and the environment (Venmalar and Nagaveni 2005).Worse still, these preservatives are not readily degraded to harmless products and are not easy to detoxify.e copper based preservatives are also poor inhibitors of mould (Arango et al. 2005) and are very costly.e dangers posed to wood treatment workers by most of the conventional proprietary wood preservatives, in addition to environmental degradation are becoming a matter of major concern worldwide (Barnes 1992).
ere are wood species that are naturally resistant to bio-deterioration agents.e resistance is mainly due to the accumulation of extractives in the heartwood, some of which are decay inhibitors (Kityo and Plumptre 1997).It is these extractives which render the heartwood unpalatable to wood destroying organisms.Hinterstoisser et al. (2000) noted that the content of extractives plays a key role in the prediction of the durability of wood.e concentration of extractives varies among species, between individual trees of the same species and within a single tree.
ere are several advantages of using wood extractives as preservatives to enhance the service life of wood.For example, wood extracts have been reported to be relatively safer than synthetic preservatives, but still e ective against plant pathogens (Arango et al. 2005).Barnes (1992) noted that extractives are organic based preservatives produced by nature and might be easier to detoxify and dispose o without adverse environmental e ects.e aim of this study was to assess the use of wood extractives as wood preservatives in increasing the service life of susceptible timber species.

Selection of sample trees and sample preparation
e outer heartwood of mature trees of Milicia excelsa (Welw.)C. Berg, Markhamia lutea (Benth.)K.Schum.and Albizia coriaria Welw.ex Oliver were selected for the study based on their known natural durability.Two mature defect free trees of each species with diameter of 80cm and above were selected from Mukono District.e trees were converted into timber by pitsawying.e heartwood was selected for the study.e timbers selected for the study were planed and cut into small test specimens of 10 x 5 x 5cm.Each sample set was labeled for ease of future identi cation.
Pinus caribaea Morelet and Antiaris toxicaria Lesch trees have low durability and were selected for the study to test for the e ectiveness of the extracts.Two mature trees with diameter above 40cm were obtained from Kifu forest in Mukono district and converted to timber.Only the sapwood from the butt end was selected for the study because it is very susceptible to insect and fungal attack (Kityo and Plumptre 1997).ey were planed and cut into small test specimens, with dimensions of 10 x 5 x 5cm.

Extraction of durable species
Two hundred grams of the samples of each durable wood species were placed in the soxhlet extractor at a time and extracted with 150ml of hexane, acetone and distilled water respectively according to ASTM D1413 (2003) standards.During extraction, one solvent was used at a time and later replaced with another a er washing the apparatus to avoid contamination.A total of nine wood extracts were obtained.Each extract was kept separately in the dark under refrigeration at 10-15 o C.

Treatment of samples with extracts
Ten test specimens of each of the two less durable timber species in the study were randomly selected from the samples and treated with hexane, acetone and distilled water extracts from M. excelsa, M. lutea and A. coriaria.As a control, ten specimens of each less durable species were exposed to the termites without any treatment.A total of 100 samples of each less durable species were treated.Treatment involved total immersion of the specimens in a bath of extracts for 5 days until a constant weight was achieved.is method compares to the results got with pressure impregnation of chemicals during wood preservation (Ibach 1999, Roll 2003).Four percent Copper Chromium Arsenate (CCA) a known preservative was also used as a control to compare the level of e ciency with extracts.
A er treatment, the test specimens were air dried, then oven dried at 60 o C for 10 hours, until a constant weight was achieved.A lower temperature was used so that extractive compounds were not lost through evaporation, degradation or by high temperatures.e specimens were then relabeled, conditioned to equilibrium moisture content and weighed to determine their initial weight W 1.

Field trials
e test specimens were then end painted with di erent colors for easy identi cation (Bultman and Southwell 1976) labeled and then exposed to termites in the eld.Field trials were preferred to laboratory studies because they allow the collective and cumulative e ects of all kinds of abiotic and biotic deterioration factors to be evaluated (Peralta et al. 2003).ey also give reliable data regarding natural resistance of wood (Bultman and Southwell 1976).
e e ect of extractives on natural durability was also tested by exposing hardwoods whose extracts had been removed to termite attack.Ten specimens of the studied hardwood species that had been extracted with water, hexane or acetone were exposed to the same termites that were exposed to the less durable species.e total number of hardwood samples was ninety with a 3 x 3 x 10 treatment structure.Ten specimens of each species that was not extracted were also exposed to these termites as control.

Study area description and arrangement of samples in the eld
e eld site was in Kilungu village, Nama sub county in Mukono district, Uganda where large infestation of Macrotermes bellicosus (Smeathman) termites had been detected earlier during preliminary studies.Samples were arranged randomly in the eld (Figure 1).e experiment was carried out in an enclosed farm with a fence that helped keep away grazing animals.e samples were then covered with grass, and tree branches to attract termites and prevent grazing animals from disturbing them.Samples were exposed during the dry season, a period when termite infestation is high.

Data collection procedures and Analysis
Inspection of samples was done daily to monitor the level of termite attack.A er 7 days of exposure, remaining samples were removed, cleaned, air dried and oven dried for 14 hours at 60 o C to obtain a constant weight.A er conditioning to equilibrium moisture content (EMC), samples were again cleaned of all soil and weighed to determine their nal weight W 2. e percentage weight loss for individual test pieces was determined according to D1413 American standards (2003).Data was analyzed using two way ANOVA and Least Square Di erence.

E ect of treatment of less durable species with wood extractives
Average weight loss for A. toxicaria and P. caribaea treated with CCA (a well known e ective wood preservative) was 4.35 and 0.94 percent respectively a er exposure to termite attack.On the other hand, the untreated control samples were completely destroyed in the same period of exposure (Figure 2). is indicates that these two species are very susceptible to attack by termites.However their resistance to termite attack signi cantly improved a er treatment with CCA preservative.
Key: 1 = M. excelsa; 2 = A. coriaria; 3 = M. lutea Average weight loss for A. toxicaria and P. caribaea treated with wood extractives was 57.3 and 40.2 percent respectively a er ve days of exposure to termite attack (Figure 2).Analysis of variance (Table 1) shows that the resistance to termite attack of A. toxicaria and P. caribaea increased signi cantly a er treatment with wood extractives (F value of 9.78 and P < 001).
However, the increase in resistance to termite attack was less e ective than in CCA treatment.A two way analysis of variance also showed that the extraction method signi cantly a ected the e ectiveness of the extracts (P < 0.05) while the species from which the extract was obtained had no signi cant e ect at 5% level of signi cance (P = 0.695) as shown in table 1. is may be attributed to the fact that di erent solvents remove di erent combinations of chemicals from the wood.e interaction between species and treatments was also found to be signi cant (P<0.01)F=3.16. is is probably because di erent solvents extracted di erent compounds from the durable woods that later improved the less durable wood species. is interaction could also be attributed to di erences in permeability of the less durable tree species.ere could have been better penetration in samples that showed a higher level of protection.
A pair wise comparison of means using the Least Signi cant Di erence (LSD) statistical test shows that the most e ective chemicals were those extracted using acetone from M. excelsa and A. coriaria (Table 2).e samples treated with these extracts showed signi cant less weight loss compared to water and hexane.Onuorah (2000) also found out that heartwood extract of Erythrophleum suaveolens (Guill.& Perr.)Brenan and Milicia excelsa when applied to less durable sapwoods were e ective in suppressing attack of either Lenzites trabea or Polyporous vericolour fungal species.In their study on the e ect of wood extracts on growth and cellulase production of strains of Bacillus subtilis, addition of wood extract signi cantly inhibited the growth of Bacillus strains (Femi-ola and Aderibigbe 2008) con rming their e ectiveness.
Resistance of these woods to termites a er preservation could be due to the extractives repellent characteristics.e repellent characteristics could be due to the toxic chemical composition of the various wood extractives and the durability of the heartwood of the tree species from which they were extracted.is is in support with Taylor et al. (2006) who in their study suggested that the methanol-soluble extractives of uja plicata and Chamaecyparis nootkatensis play an important role in heartwood resistance to attack by Coptotermes formosanus and Postia placenta.ey further noted that methanol soluble extractives of the heartwood of those tree species were positively correlated with both termite and decay resistance.
Chemical combinations of the several wood extractive components could probably be the reason for the improvement of resistance to termites by the less durable sapwoods.is is because di erent compounds obtained by the di erent extracting solvents show di erent e cacy towards termite resistance.Since there are many di erent compounds present in wood extractives, it was not possible to determine the active chemicals that are toxic to termites.Taylor et al. (2006) also concluded that it was not possible to focus on a single heartwood extractive measurement in order to understand the natural durability but on their combination.
Resistance of P. caribaea to termite attack a er treatment with wood extracts was signi cantly higher than in A. toxicaria treated with same extracts.Pinus caribaea had better protection than A. toxicaria probably due to better penetration of extracts during immersion.is could be due to the fact that P. caribaea is more porous than A. toxicaria hence was able to take in more extractives than A. toxicaria.
Extractives with which susceptible timbers were treated would not o er a practical alternative to CCA treatment.e extractives did not render the susceptible timbers resistant enough to termite attack to o er a reliable alternative to standard wood preservatives. is resistance could be achieved by using di erent durable timbers as a source of extractives than the ones chosen for this study or a combination of di erent extractives from various durable woods.e critical components in the extracts will need to be chemically identi ed and synthesized for use as preservatives. is can be very practical if some of the synthetic preservatives are banned from Uganda.

E ect of removing wood extractives from durable species
Removing combined extractives of durable hardwoods reduced their resistance to termite attack.Average weight loss of the hardwoods a er extraction is shown in gure 3. Average weight loss of the control samples of M. excelsa, A. coriaria and M. lutea were 0.9%, 2.1% and 2.4% respectively.Markhamia lutea samples were less resistant to termites a er removal of extractives followed by A. coriaria and lastly M. excelsa. is may be attributed to the extractive composition of these woods and the solvents that were used to extract them.One solvent could have failed to extract some components compared to another.
Average weight loss for M. excelsa samples was 6%, 26.2% and 8.3% (Figure 2) a er extraction with hexane, distilled water and acetone respectively.Milicia excelsa, extractives were more soluble in water followed by acetone and lastly hexane.Removal of water extracts from M. excelsa a ected those specimens negatively.Average weight loss for A. coriaria samples was 6.5%, 6.8% and 4.1% a er extraction with hexane, distilled water and acetone respectively.Albizia coriaria extracts were most soluble in water and hexane.Average weight loss for M. lutea was 21.7%, 13.3% and 20.6% (Figure 2) a er removal of extractives with hexane, distilled water and acetone respectively.Markhamia lutea extracts were most soluble in acetone and hexane than in water.
Resistance of durable tree species against termite attack is signi cantly di erent with or without extractives (Table 3).Treatment of durable tree species by removal of their extractives reduced their resistance to termites signi cantly (P < 0.05).In other words, removal of extractives increased susceptibility of durable species to termite attack.e null hypothesis is rejected since removal of wood extractives from durables species reduced their durability to termite attack.e control samples of hardwoods exposed to termites without extraction were not signi cantly attacked by the termites.Milicia excelsa was the most resistant followed by A. coriaria and lastly M. lutea.However, a er extraction, there was a decrease in level of resistance to termites as the durable wood was still relatively resistant.It could be due to the fact that extracts embedded in the cell wall could not be removed.is resistance could also be attributed to their high densities that they are able to remain durable even a er extractive removal.Wood density a ects the permeability of wood hence solvents used could not be able to remove all the extractives.is is in support with Peralta et al. (2003) who deduced that wood density is a determining factor of natural resistance of wood to termites.Solubility of extractives in polar solvents reduced the resistance of durable species to termites in this study.Taylor et al. (2006) observed that most extractives in the heartwood of T. plicata and C. nootkatensis were methanol soluble and their removal reduced the durability of those wood pieces to fungal decay and termite attack.e resistance of the durable wood samples reduced with extraction which con rms that most of their heartwood extractives responsible for termite resistance were removed.It is not solely the amount and toxicity of extractives in the heartwood that gives heartwood termite resistance, but the extractives combined toxicity and antioxidant properties (Schultz et al. 2008, Ragon et al. 2008, Pereira et al. 2009)

CONCLUSIONS AND RECOMMENDATIONS
e study showed that resistance of perishable tree species signi cantly increased a er treatment with extracts from durable tree species.Toxicity of the chemicals depended on the tree species from which the extract was obtained and the solvent used for extraction.It also showed that durability of M. excelsa, A. coriaria and M. lutea reduced a er removal of their extractives but not signi cantly possibly because extractives embedded in the cell walls were not readily removed by extraction.It is recommended that a similar study be carried out to determine the e ectiveness of the extracts to fungi.

Figure 1 .
Figure 1.Arrangement of samples in the eld.

Figure 2 .
Figure 2. E ectiveness of the various wood extractives on P. caribaea and A. toxicaria.

Figure 3 .
Figure 3.Comparison of percentage weight loss of the durable tree species with extraction solvent used.

Table 1 .
Analysis of Variance for weight loss of less durable species.

Table 2 .
Goktas et al. (2007)milar results were reported byGoktas et al. (2007)who evaluated the wood preservative potentials of Sternbergia candidum Mathew Et T. Baytop extracts.Weight losses for all treated samples decreased signi cantly con rming the e ectiveness of extract solution in enhancing decay resistance.
Di erences larger than 0.255 are signi cant at α = 0.05 level and are indicated with * Wood extractives were found to increase resistance to termite attack in both P. caribaea and A. toxicaria by 50%.

Table 3 .
Analysis of Variance of Weight loss for durable species.