Electroantennographic bioassay as a screening tool for host plant volatiles

Authors: Beck, John; Light, Douglas; Gee, Wai

Submitted to: Journal of Visualized Experiments
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/30/2011
Publication Date: 5/6/2012
Citation: Gee, W.S., Light, D.M., Beck, J.J. 2012. Electroantennogram bioassay as a screening tool for host plant volatiles. Journal of Visualized Experiments. 63:e3931.

Interpretive Summary: Plant odors play an important role in mediating plant-insect interactions. Herbivorous insects use plant odors to locate their host plant. A host plant serves as a source of food, shelter, mate, or lay eggs. When a host plant is an important agronomic or economic commodity feeding damage by these insects can inflict serious economic losses to growers. Accordingly, host plant odors can be used as attractants to attract or confuse these insects and, thus, offer an environmentally friendly alternative to pesticides for insect control. Unfortunately, plants can emit odors comprised of hundreds of compounds. The make up and ratio of odor emissions can vary depending on the developmental stage of the commodity or even the time of day. This makes identification of any biologically active component or blends of odor components an arduous process. To help identify the bioactive components of host plant odor emissions we employ the laboratory-based screening bioassay electroantennogram (EAG). EAG provides an indication of the insects’ preference (likes and/or dislikes) for odors and is an effective tool to evaluate and record the electrophysiological responses of an insect via antennal receptor sites. The EAG helps to reduce the number of odors so as to identify the promising bioactive components. However, the EAG bioassay only provides information about receptor site activation. It does not provide information about the type of behavior the compound elicits in the insect; which could be as an attractant, repellent or other type of behavioral response. Odors that elicit a noteworthy response by EAG, relative to an appropriate positive control, should be taken on to further testing such as an assay that measures behavioral response of the insect pest. This experiment will demonstrate the method used to screen almond-based host plant odors by measurement of the electrophysiological response of adult insect pest navel orangeworm (Amyelois transitella) antennae to single components and complex, natural odor bouquets via EAG bioassay. The method to be demonstrated excises the antennae from the insect followed by placement on a “fork” probe.

Technical Abstract: Plant volatiles play an important role in plant-insect interactions. Herbivorous insects use plant volatiles, known as kairomones, to locate their host plant. When a host plant is an important agronomic or economic commodity feeding damage by these insects can inflict serious economic losses to growers. Accordingly, kairomones can be used as attractants to lure or confuse these insects and, thus, offer an environmentally friendly alternative to pesticides for insect control. Unfortunately, plants can emit hundreds of volatiles. The composition and ratio of volatile emissions can vary depending on the phenology of the commodity or even the time of day. This makes identification of any biologically active component or blends of volatile components an arduous process. To help identify the bioactive components of host plant volatile emissions we employ the laboratory-based screening bioassay electroantennogram (EAG). The EAG is an effective tool to evaluate and record the electrophysiological responses of an insect via antennal receptor sites. The EAG helps to reduce the number of volatiles so as to identify the promising bioactive components. However, the EAG bioassay only provides information about receptor site activation. It does not provide information about the type of behavior the compound elicits in the insect; which could be as an attractant, repellent or other type of behavioral response. Volatiles that elicit a noteworthy response by EAG, relative to an appropriate positive control, should be taken on to further testing such as an assay that measures behavioral response of the insect pest. This experiment will demonstrate the method used to screen almond-based host plant volatiles by measurement of the electrophysiological response of adult insect pest navel orangeworm (Amyeloistransitella) antennae to single components and complex, natural volatile bouquets via EAG bioassay. The method to be demonstrated excises the antennae from the insect followed by placement on a “fork” probe.