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Title: Associative learning of host-plant chemical stimuli in immature glassy-winged sharpshooter.

Author
item Patt, Joseph - Joe
item SETAMOU, MAMOUDOU - TX.A&M UNIV, KINGSVILLE

Submitted to: CDFA Pierce's Disease Control Program Research Symposium
Publication Type: Proceedings
Publication Acceptance Date: 11/5/2006
Publication Date: 12/5/2006
Citation: Patt, J.M., Setamou, M. 2006. Associative learning of host-plant chemical stimuli in immature glassy-winged sharpshooter. CDFA Pierce's Disease Control Program Research Symposium. November, 27-29, 2006, San Diego, California. p. 25.

Interpretive Summary: The nutritional requirements of immature glassy winged sharpshooter (GWSS) constrain their diet to plants with low amide- and high amino-acid concentrations in the xylem fluid. To obtain a balanced level of nutrients, nymphs may frequently need to switch host-plants. Locating host-plants that are physiologically suitable with respect to providing adequate levels of xylem nutrients may require that the nymphs integrate information from several types of host-plant stimuli. For example, nymph response to foliar colors is enhanced by the presence of host-plant volatiles. The ability to learn to recognize stimuli associated with suitable host-plants would facilitate detection and location of host-plants whose distribution varies temporally and spatially within the nymphs' environment. The goals of our ongoing study are to determine whether nymphs can associatively learn to recognize olfactory stimuli produced by host plants and, if so, to evaluate the relative importance of olfactory conditioning in host-plant recognition.

Technical Abstract: The objectives of this study are to determine whether nymphs can associatively learn to recognize olfactory stimuli produced by host plants, and to evaluate the relative importance of olfactory conditioning in host-plant recognition. To provide nymphs for testing, second to fourth instars were placed on cowpea (Vicia unguiculata) sprigs for 1.5 days. The cut-ends of the sprigs were immersed, either, in hydroponic solution containing a low concentration of vanilla extract, or, as a control, in hydroponic solution alone. After removal from the sprigs, the nymphs' responsiveness to a pale green disk in the presence of vanilla extract odor was tested in an olfactometer using no-choice tests. In preliminary tests with blank air, 44% of nymphs from the control group jumped to the pale green target, demonstrating that innate attraction to this color is low. Vanilla extract constituents were detected by gas chromatography-mass spectrometry analysis of ethanolic extractions made from vanilla-treated cowpea sprigs. Nymphs that fed on plant sprigs with vanilla-flavored xylem fluid were significantly more attracted to the pale green target than nymphs that fed on control sprigs with non-flavored xylem fluid. However, there was no difference between individuals in the experimental and control groups with respect to the amount of time they required to orient and jump to the visual target. The finding that nymph response to a non-attractive color was enhanced following ingestion of a novel flavor, indicates that immature GWSS are capable of olfactory conditioning. Rapid population growth of GWSS may depend on the close proximity of host plants suitable for successful juvenile development. Therefore, understanding the mechanisms by which nymphs locate their host-plants is fundamental to developing vegetation management programs aimed at suppressing their population growth and dispersal in complex landscapes.