Neonate Plutella xylostella Responses to Surface Wax Components of a Resistant Cabbage (Brassica oleracea)

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Behavior of neonate Plutella xylostella was observed and quantified during the first 5 min of contact with cabbage surface waxes and surface wax components deposited as a film (60 μg/cm2) on glass. The time larvae spent biting was greater and the time walking was less on waxes extracted from the susceptible cabbage variety, Round-Up, than on an insect-resistant glossy-wax breeding line, NY 9472. The waxes of both cabbage types were characterized and some of the compounds present at higher concentrations in the glossy waxes were tested for their deterrent effects on larvae by adding them to the susceptible waxes. Adding a mixture of four n-alkane-1-ols or a mixture of α- and β-amyrins to wax from susceptible cabbage reduced the number of insects biting and, among those biting, reduced the time biting and increased the time walking in a dose-dependent manner. Among individual n-alkane-1-ols, adding C24 or C25 alcohols reduced the number of insects biting but only adding C25 alcohol reduced the time spent biting among those insects that initiated biting. Adding a mixture of five n-alkanoic acids did not affect biting, but increased the time spent palpating and decreased walking time. Among individual n-alkanoic acids, only adding C14 significantly increased the time palpating. If the observed responses were gustatory, the results indicate that some primary wax components, including specific long-chain alkyl components, have allelochemical activity influencing host acceptance behavior by a lepidopteran larva.

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