Amino Acid Fluctuations in Young and Old Orange Trees and Their Influence on Glassy-Winged Sharpshooter (<Emphasis Type="Italic">Homalodisca vitripennis</Emphasis>) Population Densities |
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Authors: | J L Bi S J Castle N C Toscano |
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Affiliation: | (1) Department of Entomology, University of California, Riverside, CA 92521, USA;(2) Arid-Land Agricultural Research Center, USDA-ARS, Maricopa, AZ 85239, USA |
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Abstract: | The glassy-winged sharpshooter (GWSS) is an invasive insect pest in California that proliferated in citrus while incorporating
many other plant species in its host range. Field studies were conducted from September 2002 to September 2003 in adjacent
young and old orange groves to determine the influence of amino acid concentrations in the xylem fluid on relative densities
of the xylophagous GWSS. Beginning in early September 2002, higher densities of adult GWSS were observed on young compared
to old trees. This difference became increasingly pronounced through late October in conjunction with increasing concentrations
of essential amino acids in xylem fluid of the young trees. Greater densities of adult GWSS remained on young trees through
early February 2003. Thereafter, the population crashed unexpectedly, leaving only negligible numbers of GWSS on either young
or old trees. Mean concentrations of the essential amino acids for insect growth and development were higher in young compared
to old trees. Besides these essential amino acids, asparagine, serine, glutamine, and tyrosine were also significantly higher
in young trees during the September–February period when GWSS was present. The pattern of elevated amino acid concentrations
in young trees continued through the entire year irrespective of the presence or absence of GWSS. Principal component analysis
followed by factor analysis revealed three factors for young or old orange trees that accounted for 81.6 and 78.9% of the
total variation in the young and old tree analyses, respectively. Various groups of amino acids in different factors displayed
peak or elevated levels in young trees corresponding to the increased densities of GWSS. The potential roles of these amino
acids in GWSS host selection are discussed. |
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Keywords: | Homalodisca vitripennis GWSS densities Orange Free amino acids Orange-GWSS interactions |
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