Leaf disk choice test

We will perform the Leaf disk test, also known as leaf disk assay or leaf disk choice test, the second of two bioassays of tannins in the diet of insects in this book. In this often used bioassay, leaf sections of a standard size are treated with the compound(s) in question. Several circular leaf sections ( leaf disks ) (Ali et al. 1999, Filho and Mazzafera 2000, Shields et al. 2008, Wheeler and Isman 2000) or cellulose membrane filters (Hollister and Mullin 1999, Larocque et al. 1999) are presented to a caterpillar in a choice experiment. We measure how much chow the caterpillar has consumed and whether any feeding inhibition is concentration dependent. Regardless of what compounds are being tested, leaf disk tests serve as an important tool in bioassaying feeding inhibitors and stimulants in insects. The cited references are examples of such studies. (In the first tannic acid experiment - Chap. 18 - the tannic acid was mixed into diet in varying concentrations.)... 

Leaf disk test A caterpillar of the tobacco homworm faces a choice of four leaf disks in a Petri dish. The leaf disks are treated with different concentrations of tannic acid ... 

Food deprivation prior to the bioassay may be desirable to increase overall activity, but hunger also may lower discrimination. Again, pilot tests can be run to determine if deprivation affects behavior. Tests are often terminated when 50% of either substrate in a choice trial is consumed. This ensures that apparent discrimination will not be lost if insects entirely consume the preferred substrate, followed by the less-preferred substrate simply due to hunger (Jermy et al. 1968). Water may need to be provided during the test but may not be needed with artificial diets or with turgid leaves. For studies with leaf disks or excised leaves without additional water, it is usually necessary to maintain high humidity, for example, with moistened filter paper lining the test arena to avoid desiccation of leaf material. 

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