## 3 Results and Discussion  
The values of untreated wood densities of sengon, jabon, mangium and pine were 0.29, 0.31, 0.60, and 0.67 g-cm\({}^{-3}\), respectively, which were similar to those reported by [PERSON] et al. [3]. All wood specimens were cut from fast-growing young tree species therefore the wood was classified as low to medium density.  
Weight percent gain (WPG) for each species was determined by weighing the specimens before treatment at oven-dried condition (W\({}_{1}\)). Later the oven-dried weight of each sample was also determined following impregnation with FA (W\({}_{2}\)) and WPG values were calculated based on the following formula:  
\[\text{WPG (\%)}=(\text{W}_{2}-\text{W}_{1})/\text{W}_{1}\times 100\%. \tag{2}\]  
Furfuryllated wood samples were darker in color than that of untreated samples, which was in line with findings of [PERSON] et al. (2005) [3]. Also, tests of [PERSON] et al. (2014) showed that FA treated with only 50% FA solution, resulted in darker specimens. The dark color of the samples is generated by the conjugated structure derived from the alphatically linked poly-furfuryl alcohol [17]  
It was found that the WPGs of sengon, jabon, mangium, and pine were 62.1%, 133.7%, 20.1%, and 33.3%, respectively. Since lower-density wood has more void space larger volume could be  
Figure 1: Subterranean termite field test.  
occupied by a liquid. Sengon had a much lower WPG than jabon despite both types of wood having similar densities. This could possibly due to and interlocking grain orientation of sengon and its high extractive content [18]. Pari reported that sengon heartwood contained 19.6% extractive substances soluble in NaOH, including carbohydrate derivatives (cellobiose, glucose, xylose, arabinose, ribose, oligosaccharidesacharide, and pentasaccharide), and long-chain fatty acid (capriate, myristic acid, myristoleic acid, pentadecylic acid, palmitic acid, margaric acid, stearic acid, oleic acid, linoleic acid, and arachidonic acid) [19]. In a previous work, it was determined that the extract of jabon wood contained phenol (pyrocatech, 4-methyl catechol, 2-methoxy-4-methyl phenol, and 4-methoxy phenol), phenolic acid (quinic acid), long long-chain fatty acids (hexadecanoic acid, linoleic acid, stearic acid, and methyl linolenic acid), carboxylic amine acids (carbamic acid), carbohydrate derivatives (levoglucosan and mome inositol), and coumarin (scopoletin) [20].  
Mangium and pine had lower WPGs, which was likely because they had much higher densities than those of sengon and jabon. Despite having a higher density of pine being a softwood had a higher WPG than mangium in this study. This finding can be explained by pine being a softwood, unlike hardwood species, mangium. Typically softwoods have less complicated anatomical characteristics than hardwoods, thus they are easily penetrated by liquid or gaseous substances during any treatment processes.  
Gross retention or retention is the amount of preservative mass in kg which entering into the 1 m\({}^{3}\) wood as function of concentration of preservative and it was calculated using the following formula:  
Gross retention (kg\(\cdot\)m\({}^{-3}\)) = [entered preservative to the wood (kg)/volume of wood the wood (m\({}^{3}\))] \(\times\) concentration of preservative. Gross retention values of imidacloprid preservative in sengon, jabon, mangium, and pine were 6.29, 12.51, 6.06, and 8.85 kg\(\cdot\)m\({}^{-3}\), respectively,