Populations of the Eastern subterranean termite, Reticulitermes flavipes, are widespread throughout most of the eastern United States. Subterranean termites have the ability to survive flooding conditions by lowering their metabolism. This lesson investigates the connection between the ability of termites to lower their metabolism to survive floods and their feeding behavior. Using an incubator, Petri dishes, and different types of mulch, termite consumption can be measured and compared. These results can be analyzed with a simple statistical test to look for significance.

The ability to survive changing environmental conditions has enabled certain insects to exist for millions of years. Termites, for example, have inhabited Earth for around 200 million years, and some species have the ability to survive periods of anoxia (Henderson, 2001). Subterranean termites (Rhinotermitidae, Isoptera) are social insects that live in underground colonies. Instead of building distinct nests, subterranean termites form interconnected networks within the colony as they forage for food.

The Eastern subterranean termite, Reticulitermes flavipes, is native to the United States and is one of the most common and widespread species of termites in the eastern region of North America (Krishna & Weesner, 1970). Workers, the largest caste, feed on wood. Under normal conditions, workers can survive up to 5 years (Kowalsick, 2004).

Subterranean termites act as decomposers in the terrestrial ecosystem. They ingest cellulose and are usually attracted to decayed wood (Su, 2005). Bacteria, fungi, and protists live in the termite hindgut to break down cellulose, and the digestion process allows termites to cycle nitrogen back into the ecosystem (Curtis & Waller, 1998). It has also been shown that termites concentrate and recycle phosphorus and potassium, nutrients necessary for rich soil (Salick et al., 1983). Unfortunately, termites can also be pests.

Subterranean termites need warmth, moisture, and cellulose to survive. Landscape mulches provide all three. This can create a problem for homeowners, who often use landscape mulches around their houses to conserve water, control weeds, improve soil content, or simply enhance the appearance of their yards. Termites have been shown to consume certain mulches like pine bark, cypress, melaleuca, and pine straw (Duryea et al., 1999). Therefore, it is beneficial to understand the physiology of termites and to explore how anoxic conditions affect the consumption rate of termites.

Even though termites are attracted to the moisture that mulches provide, too much water can affect the physiology of R. flavipes. Termites have the innate ability to survive hypoxic conditions like flooding. For example, R. flavipes can survive for ~19 hours totally submerged in water. This research indicates that termites escape drowning in areas prone to flooding by entering a quiescent state instead of seeking higher ground (Forschler & Henderson, 1995). To my knowledge, no research has tested whether the feeding behaviors of subterranean termites are affected by their ability to lower their metabolism when in an anoxic environment.

This lesson will allow students to test which mulches R. flavipes prefer and whether termites that have survived a flooded environment can recover and feed at the same rate as termites that have not experienced a flooded environment. The results could lead to an interesting student discussion on new ways to control termites.

Initial Planning

I have used this lesson in both advanced and lower-level high school biology classes as well as in college biology classes for nonmajors. The activity will take a little over 2 weeks to complete, so proper planning is crucial. I set aside the majority of class time during the first and last days of the experiment. During the actual experimental time, I continue with my regularly scheduled lessons, presenting basic termite behavior and how microorganisms assist with the breakdown of cellulose in the termite gut. This research activity will allow students to (1) assess, describe, and explain adaptations that affect survival and reproductive success in relation to coevolution; and (2) investigate and analyze the interrelationships among organisms, including mutualism. Prior to the activity, I review the components of carbohydrates and the differences between prokaryotic and eukaryotic cells. In an advanced class, there may not be a need to review these concepts. Resources that would be helpful in teaching this lesson include illustrations of eukaryotic and prokaryotic cells as well as an illustration of the hindgut of a typical subterranean termite (Figure 1).

Figure 1.

Digestive processes in a lower termite as described by R. Radek (1994).

Figure 1.

Digestive processes in a lower termite as described by R. Radek (1994).

It is extremely important for the students to realize that insects, including termites, are very important to an ecosystem. However, because of termites’ ability to consume wooden structures, they can be very costly to a property owner. Most students do not realize how extraordinary the gut of a subterranean termite is. All the parts work simultaneously to assist in breaking down the cellulose from the wood. Termites and their gut symbiotes rely on one another. These points should be emphasized to students.

Instructional Activities

For this activity, you will need 32 Petri dishes, 4 different types of landscape mulch (cedar, cypress, mixed hardwood, and pine bark mulch), an incubator, 8 droppers, and preferably 3 or 4 electronic balances. You will also need R. flavipes workers. The best way to collect termites is to go out in a forested area and break into rotten wood. If a wooded area is accessible, collecting termites as a class can be exciting for students. This would provide an opportunity for a discussion on the importance of termites to an ecosystem and the locations of termite colonies. For example, R. flavipes has the remarkable ability to forage for food 75 m from the colony, so termites being found in several rotten logs may not indicate that the colony is in that exact spot (Duryea et al., 1999). These termites can also be ordered from biological supply companies such as Carolina. I have found it helpful to see whether students can think of how termites benefit an ecosystem. Table 1 is a good way to organize class ideas.

Table 1.

Pros and cons of termites, specifically subterranean termites.

ProCon
• Decomposers • Damages homes and other buildings 
• Recycles N, P, and K  
ProCon
• Decomposers • Damages homes and other buildings 
• Recycles N, P, and K  

I then show the illustration of the termite gut and explain the processes that take place in the gut. The digestive process in the termite gut is extremely complicated, but necessary to the survival of the subterranean termite. In its foregut and midgut, the termite uses its own enzymes to break down some cellulose. The cellulolytic protozoa in the hindgut also break down cellulose into individual glucose molecules. Next, each molecule of glucose ferments into two acetate compounds, two carbon dioxide molecules, and four hydrogen molecules (Brauman et al., 1992). Bacteria referred to as ectobionts or epibionts also live in or on these protozoa (Ohkuma, 2001). Some of these bacteria are responsible for converting the hydrogen and carbon dioxide products from the fermentation process into another acetate compound. The three acetate compounds made per glucose molecule are oxidized by the termite to produce carbon dioxide and water. The water aids in the respiratory system of the termite, and the carbon dioxide is used and reduced by methanogens (Brauman et al., 1992). Because lower-level high school or nonmajor college students may have trouble understanding this process, I have found it helpful to review some key terms that they should be familiar with, such as enzymes, carbohydrates, and fermentation. The instructor can decide how in depth to go when explaining this process. Figure 1 can be used for illustrative purposes. Students may find it beneficial to have a copy of this figure during the explanation.

I define anoxia and explain that some insects can survive anoxic conditions. I also explain that some insects, including termites, have the remarkable ability to survive environments where the oxygen levels are below normal levels by entering into a state of lowered metabolism. Assigned reading of the scientific papers by Forschler and Henderson (1995) and Hoback and Stanley (2001) can be used to supplement advanced high school and college classes.

It is important that students understand that the purpose of the lab is to determine whether termites will consume mulch at a lower rate if they have been in distress (postanoxic environment).

Next, I begin the actual lab by dividing the students into eight groups. How the instructor decides to do this will depend on class size. The following are instructions for how to set up the classroom lab:

  1. Lab will be divided into 2 separate experiments (Experiment 1: Normal conditions and Experiment 2: Postanoxic conditions).

  2. Groups 1–4 will be responsible for Experiment 1 and groups 5–8 will be responsible for Experiment 2.

  3. All 8 groups should have 4 Petri dishes, forceps, a 200-mL beaker with water, a dropper, and a jar of termites.

  4. The following mulches should be placed at each group’s table:

    Groups 1 and 5 – pine mulch

    Groups 2 and 6 – cedar mulch

    Groups 3 and 7 – cypress mulch

    Groups 4 and 8 – mixed hardwood mulch

For Experiment 1, groups 1–4 will weigh and record their specific type of mulch. The weight should be as close as possible to 1 g. The mulch should be placed in the dish, and 5 mL of distilled water should be added to the mulch. Each group should then carefully add 30 worker termites to the dish using forceps and place the lid on the dish. Finally, this procedure should be repeated with three more dishes, and all four dishes for each group should be placed in the incubator at 24°C.

For Experiment 2, groups 5–8 will place 30 worker termites in their dish and fill the dish with 20 mL of distilled water before placing the lid on the dish (Figure 2). Each of these groups should replicate this procedure three more times and let all the dishes sit for 1 hour. This particular step provides an opportunity for student observation and discussion. Students may observe unique behaviors of termites as their environment is being flooded. For example, I have had students observe some of the termites in a Petri dish form a clump while other termites crawl on top of the clump. The instructor could ask students to attempt to explain this behavior. After 1 hour, the water should be suctioned out of each dish using the dropper. Each group should then weigh and record their specific type of mulch for each of their dishes. Again, the pieces of mulch should weigh close to 1 g. One piece of mulch should be placed in each dish with the lid. Each group’s dishes should then be placed in the incubator at 24°C.

Figure 2.

Submerged termites in Experiment 2.

Figure 2.

Submerged termites in Experiment 2.

On days 3, 7, and 10, each group should add 5 mL to their dishes to keep the mulch moist on these days. The mulch should be taken out of the dish on day 14 and placed on paper towels to dry. The students should weigh each type of mulch on day 16 and record their data in a class spreadsheet. Table 2 shows an example of what the spreadsheet and data could look like.

Table 2.

Example of data sheet.

Mulch typeConditionsInitial Weight (g)Final Weight (g)Consumption (g)Consumption (%)
Pine Normal 0.990 0.757 0.233 23.535 
Pine Normal 1.000 0.916 0.084 8.400 
Pine Normal 1.112 1.078 0.034 3.058 
Pine Normal 1.131 1.046 0.085 7.515 
Cypress Normal 1.152 0.902 0.250 21.701 
Cypress Normal 1.063 0.369 0.694 65.287 
Cypress Normal 1.091 0.566 0.525 48.121 
Cypress Normal 1.081 0.642 0.439 40.611 
Hardwood Normal 1.162 0.952 0.210 18.072 
Hardwood Normal 1.111 1.008 0.103 9.271 
Hardwood Normal 1.042 0.870 0.172 16.507 
Hardwood Normal 1.073 0.823 0.250 23.299 
Cedar Normal 1.014 0.998 0.016 1.578 
Cedar Normal 1.011 0.792 0.219 21.662 
Cedar Normal 0.971 0.797 0.174 17.920 
Cedar Normal 1.000 0.934 0.066 6.600 
Pine Postanoxic 1.001 0.870 0.131 13.087 
Pine Postanoxic 1.052 0.992 0.060 5.703 
Pine Postanoxic 1.072 0.911 0.161 15.019 
Pine Postanoxic 1.002 0.833 0.169 16.866 
Cypress Postanoxic 1.000 0.726 0.274 27.400 
Cypress Postanoxic 1.081 0.829 0.252 23.312 
Cypress Postanoxic 1.082 0.758 0.324 29.945 
Cypress Postanoxic 1.010 0.963 0.047 4.653 
Hardwood Postanoxic 1.060 0.925 0.135 12.736 
Hardwood Postanoxic 1.134 0.967 0.167 14.727 
Hardwood Postanoxic 1.090 0.990 0.100 9.174 
Hardwood Postanoxic 1.071 1.019 0.052 4.855 
Cedar Postanoxic 1.031 0.978 0.053 5.141 
Cedar Postanoxic 1.042 0.945 0.097 9.309 
Cedar Postanoxic 1.161 1.083 0.078 6.718 
Cedar Postanoxic 1.040 0.992 0.048 4.615 
Mulch typeConditionsInitial Weight (g)Final Weight (g)Consumption (g)Consumption (%)
Pine Normal 0.990 0.757 0.233 23.535 
Pine Normal 1.000 0.916 0.084 8.400 
Pine Normal 1.112 1.078 0.034 3.058 
Pine Normal 1.131 1.046 0.085 7.515 
Cypress Normal 1.152 0.902 0.250 21.701 
Cypress Normal 1.063 0.369 0.694 65.287 
Cypress Normal 1.091 0.566 0.525 48.121 
Cypress Normal 1.081 0.642 0.439 40.611 
Hardwood Normal 1.162 0.952 0.210 18.072 
Hardwood Normal 1.111 1.008 0.103 9.271 
Hardwood Normal 1.042 0.870 0.172 16.507 
Hardwood Normal 1.073 0.823 0.250 23.299 
Cedar Normal 1.014 0.998 0.016 1.578 
Cedar Normal 1.011 0.792 0.219 21.662 
Cedar Normal 0.971 0.797 0.174 17.920 
Cedar Normal 1.000 0.934 0.066 6.600 
Pine Postanoxic 1.001 0.870 0.131 13.087 
Pine Postanoxic 1.052 0.992 0.060 5.703 
Pine Postanoxic 1.072 0.911 0.161 15.019 
Pine Postanoxic 1.002 0.833 0.169 16.866 
Cypress Postanoxic 1.000 0.726 0.274 27.400 
Cypress Postanoxic 1.081 0.829 0.252 23.312 
Cypress Postanoxic 1.082 0.758 0.324 29.945 
Cypress Postanoxic 1.010 0.963 0.047 4.653 
Hardwood Postanoxic 1.060 0.925 0.135 12.736 
Hardwood Postanoxic 1.134 0.967 0.167 14.727 
Hardwood Postanoxic 1.090 0.990 0.100 9.174 
Hardwood Postanoxic 1.071 1.019 0.052 4.855 
Cedar Postanoxic 1.031 0.978 0.053 5.141 
Cedar Postanoxic 1.042 0.945 0.097 9.309 
Cedar Postanoxic 1.161 1.083 0.078 6.718 
Cedar Postanoxic 1.040 0.992 0.048 4.615 

Have each group calculate their average values and then find the corresponding group from the other experiment to compare the values. For example:

  • Groups 1 and 5

  • Groups 2 and 6

  • Groups 3 and 7

  • Groups 4 and 8

Each group should then report their findings to the class on a whiteboard. The data from these two experiments can be subjected to an analysis of variance (ANOVA) in an advanced class, which will determine whether there is a significant difference in percentage consumed among the four types of mulches. It will also determine whether there is a significant relationship between postanoxic and/or normal termites and mulch consumption and/or survival. A Tukey test could be employed for each variable to determine whether the termites prefer one type of mulch over the others. The average consumption rates of both groups of termites can be plotted as a bar graph using Microsoft Excel (Figure 3).

Figure 3.

Average percentage of consumption under normal conditions compared with average percentage of consumption under postanoxic conditions.

Figure 3.

Average percentage of consumption under normal conditions compared with average percentage of consumption under postanoxic conditions.

Student Discussion

I find it helpful to review mutualistic relationships at the conclusion of the experiment. I also discuss the students’ results and the results from the ANOVA. There is no need to explain the ANOVA analysis to the lower-level biology classes. Finally, the students discuss whether or not flooding could be used as a control mechanism for termite invasion.

The following shows some of the post-experimental discussion questions that I have used along with some thoughts or ideas from past research to help answer them:

  1. Termites cost the U.S. close to 2 billion dollars annually (Kowalsick, 2004). What is it about landscape mulches that attract termites and may lead to house damage?

    This may be due to component factors, such as the presence of certain chemicals in the mulches. Some mulches produce carbon dioxide as they decompose, and subterranean termites are more attracted to soil that has a continual supply of carbon dioxide (Bernklau et al., 2005). Also, it is thought that termites are attracted to areas with higher concentrations of nitrogen because their natural diet is usually low in nitrogen (Potrikus & Breznak, 1981). Some types of mulches, like pine straw, put high amounts of nitrogen into the soil during the decomposition process (Duryea et al., 1999).

  2. What could happen to the microorganisms in a termite’s gut while the termite is in a flooded environment? Could the termite’s ability to digest wood be affected?

    The bacteria and protozoa living in the termite gut have the ability to survive extreme conditions like anoxia. However, they may be stressed when the termite is submerged in water because of the limited food supply. The protozoan flagellates and the bacteria in the hindgut are responsible for degrading cellulose and producing acetate as a source of carbon for the termite to absorb and use for energy (Ohkuma, 2001). If the gut symbiotes are stressed, the termite will probably be affected.

  3. According to the experiment, which mulch type would you feel more comfortable placing around your house? Do you think it is possible for some types of mulches to repel termites?

    Although some common types of mulches attract termites, other types have been shown to repel them (Duryea et al., 1999). This may be due to high concentrations of lignin, which interferes with the breakdown of cellulose in the termite digestive system (Melillo et al., 1982). It has also been shown that termites survive just as long while starving as they do while feeding on mulch, which may show that some types of mulch may not contain the essential nutrients for long-term termite survival (Long et al., 2001).

Some of these discussion questions may, in fact, lead to other experiments. For example, question 3 could lead to testing more landscape mulches to determine which mulches termites do not consume. This experiment and discussion should allow students to see that science can be exciting. I have found that students gain a new appreciation for tiny insects and the role they play in ecosystems.

References

References
Bernklau, E.J., Fromm, E.A., Judd, T.M. & Bjostad, L.B. (2005). Attraction of subterranean termites (Isoptera) to carbon dioxide. Journal of Economic Entomology, 98, 476–484.
Brauman, A., Kane, M.D., Labat, M. & Breznak, J.A. (1992). Genesis of acetate and methane by gut bacteria of nutritionally diverse termites. Science, 257, 1384–1387.
Curtis, A.D. & Waller, D.A. (1998). Seasonal patterns of nitrogen fixation in termites. Functional Ecology, 12, 803–807.
Duryea, M.L., English, R.J. & Hermansen, L.A. (1999). A comparison of landscape mulches: chemical, allelopathic, and decomposition properties. Journal of Aboriculture, 25, 88–97.
Duryea, M.L., Huffman, J.B., English, R.J. & Osbrink, W. (1999). Will subterranean termites consume landscape mulches? Journal of Arboriculture, 25, 143–150.
Forschler, B.T. & Henderson, G. (1995). Subterranean termite behavioral reaction to water and survival of inundation: implications for field populations. Environmental Entomology, 24, 1592–1597.
Hoback, W.W. & Stanley, D.W. (2001). Insects in hypoxia. Journal of Insect Physiology, 47, 533–542.
Kowalsick, T. (2004). Eastern subterranean termites. [Online.] Available at http://counties.cce.cornell.edu/oneida/home%20garden/INSECTS/Insects%20in%20the%20Home/Termites.pdf.
Krishna, K. & Weesner, F.M., Eds. (1970). Biology of Termites. New York, NY: Academic Press.
Long, C.E., Thorne, B.L., Breisch, N.L. & Douglass, L.W. (2001). Effect of organic and inorganic landscape mulches on subterranean termite (Isoptera: Rhinotermitidae) foraging activity. Environmental Entomology, 30, 832–836.
Melillo, J.M., Aber, J.D. & Muratore, J.F. (1982). Nitrogen and lignin control of hardwood leaf litter decomposition dynamics. Ecology, 63, 621–626.
Ohkuma, M. (2001). Symbiosis within the gut microbial community of termites. RIKEN Review, 41, 69–72.
Potrikus, C.J. & Breznak, J.A. (1981). Gut bacteria recycle uric acid nitrogen in termites: a strategy for nutrient conservation. Proceedings of the National Academy of Sciences USA, 78, 4601–4605.
Radek, R. (1994). Monocercomonoides termitis n. sp., an oxymonad from the lower termite Kalotermes sinaicus. Arch Protistenkd, 144, 373–382.
Salick, J., Herrera, R. & Jordan, C.F. (1983). Termitaria: nutrient patchiness in nutrient-deficient rain forests. Biotropica, 15, 1–7.
Su, N.-Y. (2005). Directional change in tunneling of subterranean termites (Isoptera: Rhinotermitidae) in response to decayed wood attractants. Journal of Economic Entomology, 98, 471–475.