	BIO 208L


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Trail following of termites

Click here for Outline of Scientific Method.

Introduction

Termites use trail pheromones to mark a trail which is followed by conspecifics. Each individual deposits a small amount of pheromone from the sternal gland onto the substrate. The insects also follow certain other chemicals. This effect can be used to show the characteristic trail-following behavior of the termites.

Area where the insects can be obtained

North America

Materials

Individuals of the common North American termite Reticulitermes flavipes. Termite species are difficult to identify correctly, but very likely termites near your home will perform in the experiment. Be careful to prevent the release of termites. They are best kept at room temperature in a sealed plastic container with the wood or paper on which they subsist kept moist.
BIC-pen

Other pens

Description of experiment

Reticulitermes flavipes is the common indigenous termite of North America. This insect responds to a component in common pen inks by following them. I have found that BIC pens work the best.

Draw a line on a sheet of paper and deposit the termite(s) on it. They will follow it. You can experiment with this by seeing the range of angles that the termites can negotiate - very sharp angles throw them off and they invariably waiver back and forth until they re-locate the trail. Observe what happens if the trail is suddenly divided into two different trails in a Y-shaped manner. One can show that magic markers, pencils, and other writing implements are not effective in eliciting the behavior.

Discussion

The only two trail pheromones identified with certainty are the unsaturated aliphatic alcohol (3Z,6Z,8E)-3,6,8-dodecatrien-1-ol and the diterpene (E,E,E)-neocembrene, which have been found in several species [1]. These compounds are very active and occur in different, sometimes unrelated, families. The necessary amount needed for trail-following can be as low as 0.01 pg/cm (pg = picogram = 10^-12 gram) trail. To positively be identified as a trail pheromone, a compound must induce trail-following and be present in the sternal gland of the termites.

Several other chemicals belonging to different classes induce trail following in termites, but in much higher concentrations than the true trail pheromones. This is different than ants, which normally follow only their own trails. The ink in the pens has ingredients which release trail-following behavior. These compounds have been described as glycol derivatives [2]. Also phthalates, ubiquitous artificial softeners of plastic, have been reported to induce trail following in the termite Zootermopsis nevadensis [3].

References

[1] J. M. Pasteels, C. Bordereau, Releaser Pheromones in Termites, in: Pheromone Communication in Social Insects (eds.: R. K. vander Meer, M. D. Breed, M. L. Winston, K. E. Espelie), Westview Press, Boulder, 1998, p. 193.

[2] G. Becker, R. Mannesmann, Investigations on the behavior of termites against some trail-forming substances, Z. Angew. Entomol. 62, 399-436 (1968) (in German).

[3] H. Hummel, P. Karlson, Hexanoic acid as component of the trail pheromone of the termite Zootermopsis nevadensis, Hoppe-Seyler's Z. physiol. Chem. 349, 725-727 (1968) (in german).

Authors

Text by: Stefan Schulz, Institut für Organische Chemie, TU Braunschweig, Hagenring 30, D-38106 Braunschweig, Germany, email: stefan.schulz@tu-bs.de

Click here for Outline of Scientific Method.

Deductive and Inductive Thinking

In logic, we often refer to the two broad methods of reasoning as the deductive and inductive approaches.

Deductive reasoning works from the more general to the more specific. Sometimes this is informally called a "top-down" approach. We might begin with thinking up a theory about our topic of interest. We then narrow that down into more specific hypotheses that we can test. We narrow down even further when we collect observations to address the hypotheses. This ultimately leads us to be able to test the hypotheses with specific data -- a confirmation (or not) of our original theories.

Inductive reasoning works the other way, moving from specific observations to broader generalizations and theories. Informally, we sometimes call this a "bottom up" approach (please note that it's "bottom up" and not "bottoms up" which is the kind of thing the bartender says to customers when he's trying to close for the night!). In inductive reasoning, we begin with specific observations and measures, begin to detect patterns and regularities, formulate some tentative hypotheses that we can explore, and finally end up developing some general conclusions or theories.

These two methods of reasoning have a very different "feel" to them when you're conducting research. Inductive reasoning, by its very nature, is more open-ended and exploratory, especially at the beginning. Deductive reasoning is more narrow in nature and is concerned with testing or confirming hypotheses. Even though a particular study may look like it's purely deductive (e.g., an experiment designed to test the hypothesized effects of some treatment on some outcome), most social research involves both inductive and deductive reasoning processes at some time in the project. In fact, it doesn't take a rocket scientist to see that we could assemble the two graphs above into a single circular one that continually cycles from theories down to observations and back up again to theories. Even in the most constrained experiment, the researchers may observe patterns in the data that lead them to develop new theories.

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