INTRODUCTION
Wood is a natural durable material produced
by trees, it is the first structural material discovered by man (Ogbogu, 1990). Wood is in the forefront of world raw
materials. It is one of the most abundant renewable raw materials in the
forest. It is cheap and easy to work and fashion into different shapes and
sizes (Ifebueme, 1993). It is a natural organic
material whose use is widely spread (FAO, 2006). In most places and phases of
use,
there is possibility of deterioration from any of biological, physical and
chemical agents (Wong et al., 2005). The most important of these agents
are the biological namely: termite and fungi which cause tremendous havoc if
the right conditions are available. Where these agents are absent, wood is
really very resistant and can survive in construction for a long time (FAO,
2006). It has been estimated that 5% weight loss from decay can result in loss
of strength as high as 50% (Jerrold, 1995). If the warm moist conditions
required for decay cannot be controlled then the use of naturally decay resistant
wood species and or chemical treatments are required to impede decay. Insects
such as termites and certain types of beetles can be damaging to mechanical
performance. Insect's infestation can be controlled via mechanical barriers,
naturally durable species or by means of chemical treatment (Anon, 2007;
Jerrold, 2005).
There are several attempts and approaches on
termite control. In the past, research was on chemical methods of control with an
obvious lack of concern over side effects caused by the use of these chemicals
(Femi-Ola et al., 2008). Researches are now focused towards alternative,
non toxic and biological methods of control. These methods
include baiting, extreme temperatures, barriers of various types and biological
control (Malaka, 1996; Peralta et al., 2004). Naturally
resistive woods and extractives have great promise for prevention of termite
attack (Nakayama et al., 2000;
Peralta et al.,
2004), these extractives in form of phenolic compounds like terpenes-and
falconoid have insecticidal activities (Nagnan and
Clement, 1990). The uses of synthetic pesticides have some benefits, but they
are also known to harm the environment, plants and animals it controls. Therefore, there
is need to develop an alternative method with low adverse effect on consumers
and one that is less persistent to the environment. These facts influence
researchers to develop interest in plants and plant products as sources of
insecticides. Plants and plant products are useful and desirable tools in most
pest management programs because they are effective and often complement the
action of natural enemies (Schmutterer, 1990; Ascher, 1993).Indigenous Knowledge (IK)
is a local knowledge that is unique to a given culture or society. This
knowledge forms information base for a given society. It is also known as ethno
science or folk science. The IK is accumulation of information in the form of
shared environmental knowledge, beliefs, rules and techniques for productive
activities.
Generally, the method used in wood
preservation against destructive insect over the years has been insecticides, these
chemicals are however expensive and have many harmful effects. Artificial insecticides can
quickly find their way into food chains and water
sources, thus creating health hazards for humans. There is also much concern
for people using pesticides. The products may be misused because the
instructions are not in vernacular and may present a problem to most users (Malaka, 1996). There are a number of harmful effects that
synthetic insecticides can have on the environment. Artificial insecticide can
kill useful insects which eat pests. In fact, even one spray can upset the
balance between pests and the useful predators. Some chemicals are highly
persistent and can stay in the environment and in the bodies of animals for
many years. Insects also become resistant to synthetic insecticides there by
requiring more powerful chemicals on continuous basis. In the light of all
these, the use of bio-insecticides becomes imperative.
All measures that are
taken to ensure a long life of wood fall under the definition of wood
preservation. Apart from structural wood preservation measures, there are a
number of different chemical preservatives and processes that can extend the
life of wood. These generally increase the durability and resistance and
protect wood from being destroyed by insect or fungus. This study will be
justifiable in bringing out the appropriate preservatives for a particular
timber treatment and also the easier way of prolonging the serviceable life
span of timber as well as making use of affordable (less expensive) preservatives for timber use.
The study is aimed to
compare the effect of one local bio insecticides (LBI) Euphobia balsamifera (Aguwa
extract), Solignum and Gamalin
on Obeche and Doka exposed
to termite.
MATERIALS
AND METHODS
Study Area
The study was
conducted in Sokoto State. The State has a land area
of 28,232.37 square kilometers, located between latitude 120N and 13058יN and longitude 40 8יE and 60 54י E. It is bordered in the North by Niger
Republic, Zamfara State to the East and Kebbi State to the South and West (SSTG, 2010). The state
has a population of 4,244,399 individuals (National Population Commission,
2006).
The climate of the
area is dry sub-humid with mean rainfall and temperature of about 550mm and
34.90C respectively (Malami and Tsoho, 2013). There are two major seasons in the state,
namely wet and dry. The dry season starts from October and lasts up to April in
some parts and may extend to May or June in other parts of the state. The wet
season on the other hand begin in most part of the state in May and last up to
September or October (SSTG, 2010). The harmattan, a
dry cold and fairly dusty wind is experienced in the state from November to
February/March; heat is more severe in March and April, but the weather in the
state is always cold in the morning and hot in the evening. The vegetation is
Sudan savannah which consists of few scattered trees, shrubs and grasses that
covers about 30% of the ground (Baba et
al., 2005).
Sampling
Dried wood samples of
Obeche and Doka were cut
into test samples measuring 10cm length, 5 x 5cm width and breadth each. Twenty
(20) defect free samples each of obeche and doka were selected (Malami and Tsoho, 2013).
Field Layout and Experimental Procedure
The treatment combination consisted of four
treatments i.e. one local bio-insecticide LBI (Aguwa
extract) two conventional insecticides (Solignum and Gamalin) and a control replicated five times and laid out
in a randomized complete block design (RCBD). The wood was exposed to termite
mound (termitaria) to test the efficacy of the
preservatives on the wood species.
The method used in applying the treatment was
the non pressure method (Brushing), in which samples
were brushed with preservatives. The dried wood species of Triplochiton
scleroxylon and Isoberlinia doka were processed into test samples
measuring 10cm in length and 5cm x 5cm in width and breath each. Twenty defect
free samples were selected from each species. Five samples of each species were
treated with Solignum, Gamalin.
Euphobia balsamifera (latex or milk) LBI
and a control. The density of the
samples was obtained from the equation of density (p=m/v). The SI unit of
kilogram per cubic centimetre (kg/m3).Five
samples each of the species were selected and treated with fresh latex of Euphobiabalsamifera
which was collected directly from the stem and small branches using knife and
applied to the samples.
Experimental field
was cleared, followed by staking of the sampling units (treated and untreated
wood samples) at random around the termite mound (termitaria)
for a period of eight (8) weeks (Mailumo and Falemera, 2013). Each sample was tagged with a label made
up of small iron bar written with black paint as follows:
DISCUSSION
It was apparent from
the results that Obeche LBI treatment, which is a water-born
preservative, attained best density than solignum which is oil-born preservative. Probably
because wood species absorb water-borne preservative more than oil-borne
preservative. This agrees with the finding of Okechalu
et al., (2013) and Kroese et al.
(2001) who reported that wood species absorb water-born preservatives more than
oil-borne preservatives. It also agrees with the findings of Mann et al. (2011) who reported that methanolic and hexane extracts of Bombax buonapozens absorbed more preservatives
than the samples treated with solignum.
With respect to the
effect of preservatives on Isoberlinia doka, lowest density loss was revealed in LBI and solignum treatments. This could be due to the fact that LBI
treatment is a water-born preservative. Consequently, high retention of solignum enhances decay resistance of wood. Which is in accordance with the finding of Prelta,
et al. (2004) who reported that solignum when used as a preservative will enable the life
time of wood to increase. This agrees with Goktas,
et al. (2007) who reported that the
effectiveness of creosote solution enhances the decay resistance of wood. This
is similar to the result obtained by Adedeji et al. (2013) who revealed that, wood of
Triplochiton scleroxylon
has the tendency of absorbing more preservatives especially water-borne
preservatives.
It
was observed that preservatives did not have any effect on the weight of Triplochiton scleroxylon used in
the experiment. This could be due to the high effectiveness of the
preservatives with respect to the absorption capacity. This agrees with the
findings of Malami and Tsoho
(2013) that solignum is a chemical preservative that
can protect wood from termite and LBI as a local preservative which has a
natural bitter taste with aroma that is allergic to termite. Similar finding
were obtained from Eruthropleuns Spp. (Mailuma,
and Falemera 2003; Malami,
2010).
With respect to the effect of preservatives on Isoberlinia
doka, highest weight loss was observed in control
treatment. This is because of the hygroscopicity of
the wood. Consequently, termite attack was generally less on treated samples
compared to the untreated samples. This confirms the effectiveness of solignum solution in enhancing the decay resistance of wood
Goktas, et al.
(2007). This is in accordance with the finding of Parelta,
et al. (2004) that solignum when used as a preservative will enable the
serviceable time of the wood to increase.
High weight loss with respect to the effect of preservatives on samples
was observed in Triplochiton
scleroxylon.
However, Isoberlinia doka showed a
better performance in all the treatment used in this study. This could be
because doka is said to have a natural bitter taste.
This agrees with the finding of Malami and Tsoho (2013) that Digitaria iburia (Ebu) had a natural
bitter taste that termite cannot afford to attack the wood. Similar finding of Okachalu, et al.
(2013) that found significant values on Jatropha curcas and Azadirachter indica after exposed to termite attack.
CONCLUSION
The
major reason for preserving wood is to increase its life span and to improve
its usefulness. The effectiveness of any wood preservative depends on the
active ingredients of the preservative itself, also on the depth of penetration
and relative properties of the wood being subjected to preservative treatment.
This study revealed that, the LBI and Solignum has a
potential of reducing termite attack on tropical hardwood. This study also
shows that Doka had the lowest weight loss than Obeche when exposed to termite attack.
From the results,
there is no need to make use of expensive treatment since LBI is effective and
less costly than Solignum. The government and
non-governmental organizations (NGOs) should give more priority and funding on
researches on LBI as wood preservative treatment, so as to reduce dependence on
inorganic substances and hence the cost of preservatives. There is need for
massive planting of this plant species (LBI) for biodiversity conservation.
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