Synergists isolated from cade oil for the parapheromone α-ionol for male Bactrocera latifrons (Diptera: Tephritidae)

Abstract

The solanaceous fruit fly, Bactrocera latifrons (Hendel), is a tephritid fruit fly of the subfamily Dacinae which does not respond to male attractants attractive to most other members of this subfamily (methyl eugenol or cuelure). Male B. latifrons have been found to be attractive to α-ionol, with the attractancy synergistically enhanced by the addition of cade oil, a destructive distillation tar of Juniperus oxycedrus L. twigs. Solvent extracts and chromatographic fractions of cade oil were tested for attractancy enhancement for α-ionol to sexually mature B. latifrons in an outdoor olfactometer and macadamia nut orchard, and chemicals were analyzed by gas chromatography–mass spectrometry (GC–MS). Approximately 220 chemicals were found in the hexane and base extracts. Profile comparison of GC–MS chromatograms and bioactivities between fractions indicated seven chemicals in cade oil likely to enhance the attractancy of α-ionol. These chemicals are 4-allyl-2-methoxyphenol (eugenol), 2-methoxy-4-propenylphenol (isoeugenol), 2-allyl-6-methoxyphenol ( o-eugenol), 2-methoxy-4-propylphenol (dihydroeugenol), 3-hydroxy-4-methoxybenzaldehyde (isovanilin), 2-butenal (crotonaldehyde), and 4-ethyl-2-methoxyphenol. Bioassays in an outdoor olfactometer and preliminary field trials of the authentic chemicals showed that eugenol, isoeugenol, dihydroeugenol, and 4-ethyl-2-methoxyphenol enhanced α-ionol attractancy up to 1.3–2.1-fold (olfactometer) or 2.0–2.4-fold (field) compared to α-ionol alone when each of them was presented together with α-ionol. The identification of eugenol as a synergist for the attractiveness of α-ionol to B. latifrons helps to better place B. latifrons in the overall Dacinae male lure response pattern.