Study area
The study was carried out in Afaka (Latitude 10.66697; Longitude 7.387451) and Samaru-Zaria (Latitude 11.166667; Longitude 7.633333), Kaduna State in the Northern Guinea Savanna vegetation zone of Nigeria. The climate is characterized by a clear distinction between dry and rainy seasons. The rainy season lasts from mid-April to early October with the months of August and March being the peak of the wet and dry seasons, respectively. The mean annual rainfall is 1266.0 mm based on annual rainfall record of forty three years (1969–2012) (NIMET 2012).
Temperatures are high throughout the year with the highest in March (about 38.6 °C) and the lowest in January (about 20.2 °C). Relative humidity in the dry season is below 10% in the afternoon and 90% at dawn. During the rainy season, the relative humidity can be over 70% in the midday and 95% at dawn.
Preparation of wood samples
The preparation of wood samples for the experiments was carried out by felling one stand each of E. camaldulensis, E. citriodora, E. cleoziana and E. tereticornis from plantations established in 1988 at Buruku experimental site of Trial Afforestation Station, Afaka, Kaduna State, Nigeria (10.6196° N, 7.2316° E). The trees were cross cut into three portions of 4 m each representing the bottom, middle and top parts. The middle portion was further cross cut into two billets of 2 m out of which 20×50×2000 mm boards were produced. Thereafter, each board was sliced into 20× 20 × 2000 mm scantlings. Wood block samples of 20× 20 × 200 mm were prepared from the scantlings and air-seasoned for two weeks before it was used for the study. The wood blocks were oven-dried at 100°C until constant weight and weighed prior to field trials.
Feeding deterrence
Feeding deterrence was carried out using wood preference and non-preference tests in a timber grave yard at Trial Afforestation Research Station premises in Afaka, Kaduna and replicated at Savanna Forestry Research Station premises, Samaru, Zaria, Nigeria (11.1667oN, 7.6333oE). For preference test, a wood block each from the four Eucalyptus species was tied together in a group representing an experimental unit. Each group was replicated ten times as a set and three separate sets were prepared for wood damage assessment at 3, 6 and 9 months. The wood blocks were arranged in a Randomized Complete Block Design, buried in the soil at 20 cm depth and at a distance of 2 m apart. Wood damage was assessed at 3, 6 and 9 months after being buried in the soil. At each assessment, the wood blocks were removed from the soil, cleaned and oven-dried at 100oC until constant weight and re-weighed to determine the weight loss. The percentage weight loss was calculated and used as the percentage of wood eaten by termites.
For non-preference field trials, the wood blocks were prepared as in preference test except that the wood block of different Eucalyptus species was buried in the soil individually at a distance of 2 m apart in the field. Each Eucalyptus species was replicated 10 times and arranged in a Randomized Complete Block Design. The experiment was replicated three times for damage assessment at 3, 6 and 9 months. The wood blocks were removed at 3, 6 and 9 months and assessed for damage as in the preference test. Data on percentage wood damage in preference and non-preference tests were transformed using arcsine before being analyzed using ANOVA and means were separated using Tukey’s HSD test (p < 0.05). Results of preference and non-preference tests were subjected to a t-test analysis for the comparison of wood damage under the two tests.
Determination of wood density
Ten wood sample specimens were prepared from each Eucalyptus species in the Department of Forest Resources Management, University of Ibadan, Ibadan, Nigeria. The wood samples were oven-dried at 103oC until constant weight was achieved. The masses (m) of the wood samples were determined accurately to the nearest 0.001g using Analytical weighing balance. The volume (v) of each wood sample was calculated by the product of the average length, average breadth and average thickness of the wood sample. A vernier caliper with the accuracy of 0.02mm was used to take the individual linear dimensions of the wood sample. The density for each wood species was calculated using the formula:
ρ= m/v
Where,
ρ = wood density
m = mass of the wood sample (g)
v = volume of the wood specimen (cm3)
Determination of wood hardness
The wood hardness of different Eucalyptus species was carried out at the Department of Metallurgical and Material Engineering, Ahmadu Bello University, Zaria, Nigeria according to the provisions in ASTM-E18-79 using Rockwell hardness tester on “F” scale (Indentec Rockwell Hardness Tester) with 1.588mm (1/16 inch) steel ball indenter, minor load of 10kg, and major load of 60kg. Before the test, the mating surface of the indenter, plunger rod and test samples were thoroughly cleaned by removing dirt, scratches and oil. The minor load of 10kg was applied to the sample in a controlled manner without inducing impact or vibration and zero reading position was established. Then the major load of 60kg was applied and the reading was taken when the large pointer came to rest. The load was removed by returning the crank handle to the latched position and the hardness value read directly from the semi-automatic digital scale (Idris et al., 2012). Hardness values were reported by writing the number followed by the letters HR for Hardness Rockwell and affixing the name of the scale (F) used (Idris et al., 2012).
Wood treatment of E. tereticornis with natural oil
Eucalyptus tereticornis has been confirmed as the most susceptible species to termite attack in preference and non-preference tests. The wood blocks were prepared as described under preparation of wood samples above. Wood blocks of E. tereticornis were oven-dried at 100oC until constant weight and weighed to determine the initial weights. After drying, the wood blocks were re-weighed; and the weights were recorded. The wood blocks were treated by submerging them separately in Solignum solution, Neem Seed oil, Jatropha Seed oil and Palm kernel oil in 2-L plastic buckets for 12 hours. The wood blocks were air-dried in the laboratory for 72 hours and re-weighed. Three sets of 10 wood blocks were treated with each preservative to be exposed to termites in the field for 6, 12 and 18 months. The treatments were arranged in a Randomized Complete Block Design in a timber graveyard. The experiment was carried out in Afaka, Kaduna and replicated in Samaru, Zaria.
At the end of each exposure periods, the wood blocks were removed and inspected for termite attack. The wood blocks were cleaned and oven-dried at 100oC until constant weight in the laboratory. They were re-weighed to determine the final weight and the percentage of wood consumed by termites was calculated. Data collected on wood damage were transformed using arcsine before analyzed ANOVA. Significant differences in wood damage were separated using Tukey’s HSD test (p < 0.05).