Effect of Tannins on Insect Feeding Behavior
The feeding behavior of herbivorous insects is guided by plant chemistry. There are specialists and generalists with regard to the range of plant species they attack. Nutrients such as sugars and proteins, and secondary plant compounds such as phenolics, terpenoids, or alkaloids, determine whether or not an insect will feed on a plant and to what extent.
To investigate food preferences by insects or other herbivores, such as deer (Rautio et al. 2008), and the compounds responsible for their choices, these compounds can be added to their diet and tested in feeding bioassays. Here we will add a mixture of phenolic compounds, known as “tannic acid,” to the diet of hornworm caterpillars. The tobacco hornworm, Manduca sexta, normally feeds on Solanaceae such as tomato or potato plants. For more on the natural history of this insect, consult the information sheet prepared by the biological supply company that ships these caterpillars.
We will perform one of the two bioassays dealing with tannins in insect diet: The compounds to be tested (tannic acid) are mixed into diet in varying concentrations. We measure how much chow the caterpillar has consumed and whether the effect is concentration dependent. (The second bioassay – in Chap. 19 – employs the Leaf disk test. In this often used bioassay leaf sections of a standard size are treated with the compounds in question.)