sp. Reticulitermes Wood Preference
Keiana Watkins
Fern Lehman
WF 1:00
Abstract
Termites are beneficial as well as detrimental to society. They help maintain
ecosystem sustainability, but also ruin man-made wood-framed structures. To prevent the
negative impact that termites can have on the lives of man, we should use the species of
wood that is less preferred. Therefore, in this experimental study, termites were
investigated to see if they showed a preference to specific species of wood and if so
which one. We predicted that the termites would show a preference to softwoods versus
hardwoods. For this experiment, ten termites of the genus Reticulitermes sp. were
randomly selected and placed in the middle of choice (4 wood types) and no choice (all
pine) chambers for 10- and 15-minute time intervals. The four different types of wood,
apple, cedar, oak, and pine, were placed in piles in the four sections within the choice
chamber and squirted with lake water to ensure that they were moist. A total of 5 trials, a
control, and 60 termites were used for each time frame. The termites tended to choose
pine and cedar over apple and oak. This data supported our hypothesis that termites
showed a preference to softwoods versus hardwoods. Knowing that termites tend to show
a preference to softwoods informs homeowners, contractors, and architects that they
should avoid these types of woods in their structures.
Introduction
Termites are major detritivoresheterotrophs that obtain nutrients by consuming
decomposing organic matterthat can cause extensive structural damage to buildings.
Studying the wood-feeding behavior of termites provides insight to architects and
homeowners globally on the necessary precautions they need to be aware of in order to
keep their properties termite free. Numerous species of woody trees have evolved and
adapted resistance to termites, which in return caused termites to develop similar
protective adaptations to guard themselves from the natural defenses of their prey.
However, natural defenses are not the only issues termites face. Man has tested the
durability of wood and wood products, finding ways to protect them from destructive
activities of termites with toxic chemicals, attractants, and repellents (Haverty and
Nutting, 1975).
Due to such adaptations, termites have developed a system of determinants to
aid in the wood selection process. According to McMahan (1966), suggested factors for
wood selection by termites in nature are moisture content, amounts and chemical nature
of the wood extracts, physical hardness, differences between heartwood and sapwood,
and the nature and extent of pre-existing fungus attack. In consideration of these factors,
there is sufficient evidence to infer that termites prefer certain types/species of wood in
comparison to others. The measurement of wood-feeding preferences exhibited by
termites can be measured in two different ways, choice or no choice experiments. In a nochoice situation, termites are introduced into an environment where only one choice of
food is available and the mass or percentage loss of the wood over a specified time is
measured. In a choice situation, the termites are exposed to two or more options and
feeding on each respective choice is evaluated (Peterson and Gerard, 2007). We will be
performing a choice experiment, in which the termites will be in a constant environment
and able to choose between four different species of wood, apple (Malus domestica),
cedar (Cedrus), pine (Pinus), and oak (Quercus). Based off the results of previous
studies, which show that termites do prefer a certain type of wood, we hypothesize that
the termites will show preference to softwoods versus hardwoods.
The termites being used in this experiment are extracted from the genus
Reticulitermes. This particular genus of termites thrives in a subterranean environment
and prefers substances that are in close contact with a source of moisture. We are using
four different types of wood that are further classified into two broader representations
depending on the density of the actual sample. Pine and cedar are classified as softwoods,
while oak and apple are classified as hardwoods. These factors will affect the type of
wood chosen. The termites will utilize pheromoneschemical substances released by an
animal that serves to influence the physiology or behavior of other members of the same
speciesto signal to the remainder of the group that it has come into contact with the
preferred wood choice. To determine exactly what the preferred wood choice is, we will
measure the how the variety of wood available, independent variable, will affect the
feeding pattern of the termites, dependent variable.
Wood is an essential part of our natural habitat as well as an economical
stimulant. Determining whether or not termites show a wood preference will benefit
numerous industries when determining the best types of woods to use for their individual
projects in attempts to avoid the costly damages termites can cause. Although termites are
known for negatively impacting the human race, they also provide very positive services
that help to cleanse our environment. Being that they are detritivores, they decompose
dead, and decaying material, which helps maintain ecosystem sustainability. They also
form symbiotic relationships with certain fungi that benefit from their presence. Although
termites pose a greater negative threat to humans, the effect that they have on the
environment as a whole is much more meaningful.
Materials and Methods
Ten worker termites of similar size were randomly selected and placed in the
middle of choice (4 types of wood) and no choice (all pine) chambers under identical
conditions (Figures 1 and 2) They were observed under 10- and 15-minute time intervals
with a total of 5 replicates and a control for each. To ensure that environmental factors,
such as light intensity, remained constant the experiment was conducted in a specific area
of the same laboratory room.
Figure 1: This is the set-up of a choice chamber. It is depicted as a choice chamber
because the termites are given a choice between several things, the various wood types.
Figure 2: This is the set-up of a no choice or control chamber. It is depicted as a
no-choice chamber because only one option is given, pine, and the termites either
choose it or not.
The first time the experiment was performed the termites were allowed 10
minutes to make their choice. A total of 5 trials were completed with each trial starting 23 minutes into the previous one. When repeating the trials the conditions were similar to
avoid any errors that might result from small changes. We cleaned each chamber with
ethanol prior to usage. Equal amounts of the various types of wood chips were added into
their corresponding sections. The same amount of each type of wood chips was used in
each trial and each chamber. Using different amounts should be avoided because the
termites may be attracted to bigger piles, which adds an outside factor influencing their
choice. Each pile of wood chips was squirted with equal amounts of pond water to ensure
that each sample is very moist. Using a paintbrush and weigh-boat, 10 termites were
collected making sure that there was a minimum amount of their feces in the sample. If
there is a significant amount of feces left the termites will not make a choice because they
will gather around the familiar scent of their own bodily waste. The termites were then
added to the middle of the chamber and we immediately begin recording the time. When
10 minutes was completed, we immediately begin to count the number of termites in each
section of the chamber and record this data in a properly formatted table. These steps
were repeated until we completed a total of 5 trials and 1 control.
For the next portion of the experiment, keeping everything consistent we
increased the time interval from 10 total minutes to 15 total minutes. The time was
increased to ensure that the termites had a sufficient amount of time to make a decision
because in there was a significant amount termites of that made no choice when given
only 10 minutes to choose. Once the 15 minutes is up record the data in a table.
Results
For the 10-minute time interval, on average, approximately 2.7 of the termites
chose pine, 1.1 chose Cedar, 1.3 chose apple, and only 0.89 chose oak (Figure 3). For the
15-minute time interval, on average, approximately 1.9 of the termites chose cedar, 1.1
chose pine, 0.7 chose apple, and only 0.5 chose oak (Figure 5). The average number of
termites that made a choice versus those that didnt make a choice, including the controls,
for each time interval was also taken. For the 10-minute time interval, on average,
approximately 2.7 termites made a choice versus 2.8 that didnt make a choice (Figure 4)
For the 15-minute time interval, on average, approximately 2.5 termites made a choice
versus the 0.8 termites that didnt make a choice (Figure 6). For each graphical
representation of the data error bars were created with 95% confidence intervals.
Figure 3: Average number of Reticulitermes sp. that showed a preference to the given
wood choices. Data selected was taken over a 10-minute time interval. The termites were
placed in the middle of a choice chamber with 4 different types of wood, oak, pine, cedar,
and apple. Each pile of wood was sprayed with lake water to ensure moisture. The
termites were given 10-minutes to make a choice and once the time frame was up they
were counted and collected. There were a total number of 5 replicates and a control and
70 termites used. Error bars were created with 95% confidence intervals.
Figure 4: Average number of Reticulitermes sp. that made a choice versus the average
number that didnt make a choice. Data selected was taken over a 10-minute time
interval. The termites were placed in the middle of a choice chamber with 4 different
types of wood, oak, pine, cedar, and apple. Each pile of wood was sprayed with lake
water to ensure moisture. The termites were given 10-minutes to make a choice and once
the time frame was up they were counted and collected. There were a total number of 5
replicates and a control and 70 termites used. Error bars were created with 95%
confidence intervals.
Figure 5: Average number of Reticulitermes sp. that showed a preference to the given
wood choices. Data selected was taken over a 15-minute time interval. The termites were
placed in the middle of a choice chamber with 4 different types of wood, oak, pine, cedar,
and apple. Each pile of wood was sprayed with lake water to ensure moisture. The
termites were given 15-minutes to make a choice and once the time frame was up they
were counted and collected. There were a total number of 5 replicates and a control and
70 termites used. Error bars were created with 95% confidence intervals.
Figure 6: Average number of Reticulitermes sp. that made a choice versus the average
number that didnt make a choice. Data selected was taken over a 15-minute time
interval. The termites were placed in the middle of a choice chamber with 4 different
types of wood, oak, pine, cedar, and apple. Each pile of wood was sprayed with lake
water to ensure moisture. The termites were given 15-minutes to make a choice and once
the time frame was up they were counted and collected. There were a total number of 5
replicates and a control and 70 termites used. Error bars were created with 95%
confidence intervals.
Discussion and Conclusion
After the experiment was completed we discovered that the termites preferred
Cedar and Pine, as opposed to Apple and Oak. We also discovered that Oak was of their
least favorite. For example based on Figure 3, Graph 1 the average number of termits that
chose pine was 2.7, which was the most favored, while Oak was only 0.89. In contrast
based on Figure 5, Graph 3 the average number of termites that chose cedar was 1.9,
almost half, opposed to the 0.5 that chose Oak. Although we had a significant amount of
termites not make a decision during the 10- and 15-minute time intervals, 2.8 and 0.8
respectively, we still believe that termites, Reticulitermes, show a preference. Both cedar
and pine are considered softwoods while both apple and oak are considered hardwoods.
Comparing this information to the results, a conclusion could be made that
Reticulitermes prefer softwoods to hardwoods. According to McMahan (1966), suggested
factors for wood selection by termites in nature are moisture content, amounts and
chemical nature of the wood extracts, physical hardness, differences between heartwood
and sapwood, and the nature and extent of pre-existing fungus attack. In consideration of
these factors, there is sufficient evidence to infer that termites prefer certain types/species
of wood in comparison to others. The error bars with 95% confidence intervals are all in
range of each other, showing no significant difference in the data. During the course of
the experiment we noticed that the termites preferred shaded environments, which the
pine and cedar piles provided exceptionally well in comparison to the oak and apple
piles. The cedar and pine piles were more shaven and therefore in greater abundance than
the oak and apple piles. The abundance and smaller chips of the cedar and pine piles
created a more compact environment, which increased the amount of shading available.
Since the particular genus of termites that we used thrive in a subterranean environment
and prefer substances that are in close contact with a source of moisture, this behavior
was not surprising.
During the course of the experiment all of the possible experimental and
environmental factors were controlled. However, there are always caveats and
improvements to be made. The moisture content of each trial may have been slightly
different due to the type of apparatus being used. To eliminate this as a possible source of
error, a certain amount of water could be measured out first and then poured on top of the
pile to ensure accuracy and consistency. Also, the condition of the wood may have played
a major role in the selection process as well. The pine and cedar samples were shaven
down to very thin pieces making them more abundant, where as the apple and oak piles
were in chip form. One very important factor that we didnt realize could affect the
experiment, as much is the pheromone on our hands. W were intimately involved in the
handling of the wood barehanded. Everyone has a specific body scent and one persons
scent may have been more appealing to the termites than others. Due to the blindness of
termites, olfactory senses are the major way in which they make decisions. To avoid this
in future experiments we will either wear gloves or wash our hands with ethanol prior to
touching the wood.
Future experimentation includes focusing on primarily softwoods or on the top
two choses, pine and cedar. Also, a different class/genus of termites could be used as
comparison data. Using a different class/genus of termites could provide insight into
whether all termites show preference to the same types of wood or whether or not it
varies among species. The importance of wood preference to the ecosystem is very
significant. According to Haverty and Nutting preference is important in accurately
determining the average turnover of dead plant material in an ecosystem. It is also
important to man because of the extensive attack termites have had on our crops and as
wells as structures and possessions (1975). Thus, understanding the wood preferences of
termites affects the environment as well as human activity.
References
Haverty, M.I. and W.L. Nutting 1975. Natural wood preferences of desert termites.
Ann. Entomol. Soc. Amer. 68: 533-536.
McMahan, E. A. 1966. Studies of termite wood-feeding preferences. Proc. Hawaiian
Entomol. Soc. 19: 239-50.
Peterson, Chris J.; Gerard, P.D. 2009. Two new termite (Isoptera: Rhinotermitidae)
feeding indexes for woods of varing palatability. Midsouth Entomologist, Vol. 1:
11-16.
Termites, A Carolina Care Sheet. Carolina Biological Supply Co. 2009. Web 7 July
2011. <http://www.carolina.com/category/teacher+resources/careguides/termites.do>