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J Chem Ecol

Title:		"Identification of Components of the Aggregation Pheromone of the Guam Strain of Coconut Rhinoceros Beetle, Oryctes rhinoceros, and Determination of Stereochemistry"
Author(s):		Hall DR; Harte SJ; Farman DI; Ero M; Pokana A;
Address:		"Natural Resources Institute, University of Greenwich, Central Avenue, Chatham Maritime, Kent, ME4 4TB, UK. d.r.hall@gre.ac.uk. Natural Resources Institute, University of Greenwich, Central Avenue, Chatham Maritime, Kent, ME4 4TB, UK. Papua New Guinea Oil Palm Research Association (PNGOPRA), Dami Research Station, PO Box 97, West New Britain Province, Kimbe, Papua New Guinea. Pacific Community (SPC), Land Resources Division, Private Mail Bag, Suva, Fiji. New Britain Palm Oil Limited, Quadalcanal Plains, PO Box 2001, Honiara, Solomon Islands"
Journal Title:		J Chem Ecol
Year:		2022
Volume:		20211111
Issue:		3
Page Number:		289 - 301
DOI:		10.1007/s10886-021-01329-z
ISSN/ISBN:		1573-1561 (Electronic) 0098-0331 (Print) 0098-0331 (Linking)
Abstract:		"The coconut rhinoceros beetle, Oryctes rhinoceros (Linnaeus 1758) (Coleoptera: Scarabaeidae: Dynastinae) (CRB), is endemic to tropical Asia where it damages both coconut and oil palm. A new invasion by CRB occurred on Guam in 2007 and eradication attempts failed using commonly applied Oryctes rhinoceros nudivirus (OrNV) isolates. This and subsequent invasive outbreaks were found to have been caused by a previously unrecognized haplotype, CRB-G, which appeared to be tolerant to OrNV. The male-produced aggregation pheromone of the endemic, susceptible strain of O. rhinoceros (CRB-S) was previously identified as ethyl 4-methyloctanoate. Following reports from growers that commercial lures containing this compound were not attractive to CRB-G, the aim of this work was to identify the pheromone of CRB-G. Initial collections of volatiles from virgin male and female CRB-G adults from the Solomon Islands failed to show any male- or female-specific compounds as candidate pheromone components. Only after five months were significant quantities of ethyl 4-methyloctanoate and 4-methyloctanoic acid produced by males but not by females. No other male-specific compounds could be detected, in particular methyl 4-methyloctanoate, 4-methyl-1-octanol, or 4-methyl-1-octyl acetate, compounds identified in volatiles from some other species of Oryctes. Ethyl 4-methyloctanoate elicited a strong electroantennogram response from both male and female CRB-G, but these other compounds, including 4-methyloctanoic acid, did not. The enantiomers of ethyl 4-methyloctanoate and 4-methyloctanoic acid were conveniently prepared by enzymatic resolution of the commercially-available acid, and the enantiomers of the acid, but not the ester, could be separated by gas chromatography on an enantioselective cyclodextrin phase. Using this approach, both ethyl 4-methyloctanoate and 4-methyloctanoic acid produced by male CRB-G were shown to be exclusively the (R)-enantiomers whereas previous reports had suggested male O. rhinoceros produced the (S)-enantiomers. However, re-examination of the ester and acid produced by male CRB-S from Papua New Guinea showed that these were also the (R)-enantiomers. In field trapping experiments carried out in the Solomon Islands, both racemic and ethyl (R)-4-methyloctanoate were highly attractive to both male and female CRB-G beetles. The (S)-enantiomer and the corresponding acids were only weakly attractive. The addition of racemic 4-methyloctanoic acid to ethyl 4-methyloctanoate did significantly increase attractiveness, but the addition of (R)- or (S)-4-methyloctanoic acid to the corresponding ethyl esters did not. Possible reasons for the difference in assignment of configuration of the components of the CRB pheromone are discussed along with the practical implications of these results"
Keywords:		Animals *Coleoptera/physiology Female Guam Male Octanols Perissodactyla Pheromones/pharmacology (R)-4-methyloctanoic acid Electroantennogram Enantioselective gas chromatography Enzymatic resolution Ethyl (R)-4-methyloctanoate;
Notes:		"MedlineHall, David R Harte, Steven J Farman, Dudley I Ero, Mark Pokana, Alfred eng 2021/11/12 J Chem Ecol. 2022 Mar; 48(3):289-301. doi: 10.1007/s10886-021-01329-z. Epub 2021 Nov 11"