Identification of pheromone synergists in American palm weevil, Rhynchophorus palmarum, and attraction of related Dynamis borassi

Thirteen host-plant kairomone blends, including 28 compounds, were tested a nd showed moderate to high synergy with rhynchophorol. The blends plus rhyn chophorol also attracted the related Dynamis borassi. Ethanol-ethyl acetate blends in various ratios showed moderate synergy. Two blends, including "c haracteristic coconut" odor molecules, were as efficient as sugarcane in sy nergizing rhynchophorol and field luring American Palm weevils (APWs). Prel iminary olfactometer tests of natural host-plant volatiles demonstrated the role of fermentation in primary APW attraction. The synergists were chosen from a comparative study of the odors emitted by four plant materials attr active to the APW: sugarcane, coconut, Jacaratia digitata tree and Elaeis g uineensis (Oil palm). The volatiles were isolated during 6 days of sequenti al trappings onto Supelpak-2 adsorbent. The highly volatile fraction of sug arcane volatiles was sampled by solid-phase microextraction (SPME). Odors w ere analyzed and identified by gas chromatography and mass spectrometry. El ectroantennogram responses to the plant odors were recorded to help in scre ening for bioactivity. The odor compositions between plants prior to and du ring fermentation were compared using a principal component analysis (PCA) to determine common odor features of the plants and to design simplified bl ends for field activity screening. About 100 components were identified in the >4-carbon fraction of the odors, among which 65% were fermentation vola tiles. Fermentation generated a strong increase in the amount and variety o f the volatiles emitted. The palm materials emitted two- to threefold great er odor amounts than the other plants. The odors from each plant were disti nct according to PCA, with few common abundant components: isopentanol, 2-m ethylbutanol, their acetates, acetoin, isobutyl acetate, 2,3-butanediol, an d 2-phenylethanol. Ethanol and ethyl acetate accounted for 80-90% in the hi ghly volatile fraction of sugarcane odors. Coconut odor was mainly characte rized by phenol, guaiacol, 1,2-dimethoxybenzene, ethyl esters of tiglic and 3,3-dimethylacrylic acids, 2-hexanone, 2-nonanone; and, to a lesser extent , by 2-heptanone, menthone, beta-phellandrene, ethyl octanoate and decanoat e, which were also present in other plants.