Day-night and phenological variation of apple tree volatiles and electroantennogram responses in Cydia pomonella (Lepidoptera: Tortricidae)

Volatile compounds from apple trees (variety Golden Smothee) were collected in the field from attached apple branches enclosed in plastic bags in the morning and at dusk and during three growth periods (after petal fall [APF], immature fruit [IF], and close-to-full ripening [CFR]). Collections were analyzed by gas chromatography-mass spectrometry (GC-MS) and gas chromatography-electroantennographic detection (GC-EAD) using the antennae of Cydia pomonella males as biological detectors. Forty-four compounds were detected in the volatile collections. The most abundant compound in all treatments was (Z)-3-hexenyl acetate, a common green leaf volatile. Other abundant compounds were (Z)-3-hexenol, (E,E)-alpha-farnesene, hexyl acetate, 4,8-dimethyl-1,3,7-non-atriene, hexyl hexanoate, and germacrene D. Most of the compounds that showed significant differences between periods were emitted in greater amounts in the APF and/or IF periods than in the CFR period. (E)-beta-caryophyllene and an unidentified compound were significantly more abundant during the day, whereas 2-hexanone, octanal, and (Z)-3-hexenol were significantly more abundant at dusk. GC-EAD responses were very weak and significantly higher than background noise only to hexyl acetate, 4,8-dimethyl-1,3,7-nonatriene, nonanal, (Z)-3-hexenol, hexyl butanoate, and (E,E)-a-farnesene. In further electroantennographic (EAG) assays with synthetic compounds, high responses by the antennae of both males and females were recorded to many of the compounds identified. Males showed a response equal to or higher than females to all compounds except beta-myrcene.