A sensitive bioassay for spider mite (Tetranychus urticae) repellency: a double bond makes a difference
2011
Snyder, John C. | Antonious, George F. | Thacker, Richard
Choice bioassays were used to determine repellency of homologous n-alkanes (C8H18–C21H44) to spider mites. When tested at 400 μg/cm2, the C15–C19 alkanes were highly repellent; the C16 n-alkane, n-hexadecane, was most repellent. Subsequently the EC50 values, the concentration at which 50% of the mites were repelled, were determined for the C15–C19 n-alkanes and their analogous 1-n-alkenes (C15H30–C19H38). The EC50 value for 1-heptadecene, the C17 1-n-alkene, was the lowest observed. Except for the 17-carbon hydrocarbons, the EC50 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 EC50 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.
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