title: A sensitive bioassay for spider mite (Tetranychus urticae) repellency: a double bond makes a difference.
abstract: Choice bioassays were used to determine repellency of homologous n-alkanes (C(8)H(18)-C(21)H(44)) to spider mites. When tested at 400 μg/cm(2), the C(15)-C(19) alkanes were highly repellent; the C(16) n-alkane, n-hexadecane, was most repellent. Subsequently the EC(50) values, the concentration at which 50% of the mites were repelled, were determined for the C(15)-C(19) n-alkanes and their analogous 1-n-alkenes (C(15)H(30)-C(19)H(38)). The EC(50) value for 1-heptadecene, the C(17) 1-n-alkene, was the lowest observed. Except for the 17-carbon hydrocarbons, the EC(50) values for the n-alkanes were less than those for their analogous 1-n-alkenes. Depending on the compounds evaluated, there was as much as a six-fold difference of repellency between an n-alkane its analogous 1-n-alkene. Thus, the bioassay has sufficient sensitivity to detect behavioral differences associated with the presence or absence of a single double bond. The EC(50) values for the most repellent hydrocarbons were similar to that reported for 2,3-dihydrofarnesoic acid, a naturally occurring repellent isolated from trichome secretions of a wild tomato, Solanum habrochaites, and also were similar to concentrations used to evaluate arthropod repellents. Consequently, this bioassay may be useful for providing a better understanding of the relationships between structures and activities of natural products that are repellent to spider mites.
authors.affiliation: Department of Horticulture, N318 Ag. Sci. N., University of Kentucky, Lexington, KY 40546-0091, USA. snyder@uky.edu
authors.forename: John C
authors.initials: JC
authors.lastname: Snyder
authors.forename: George F
authors.initials: GF
authors.lastname: Antonious
authors.forename: Richard
authors.initials: R
authors.lastname: Thacker
mesh_terms: D000473:Alkanes / Q000737:chemistry*; D000818:Animals; D001681:Biological Assay; D005260:Female; D010575:Pesticides / Q000032:analysis*; D040102:Tetranychidae
chemical_list: D000473:Alkanes; D010575:Pesticides