Sex pheromone chemistry and field trapping studies of the elm spanworm Ennomos subsignaria (Hübner) (Lepidoptera:Geometridae)
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The elm spanworm, Ennomos subsignaria (Hübner), occurs throughout Canada and the eastern United States and can be a destructive forest pest on a wide range of deciduous trees. Gas chromatography/mass spectrometry (GC/MS) and coupled gas chromatographic–electroantennographic detection (GC/EAD) analysis of pheromone gland extracts, in combination with chemical synthesis and field trapping studies have identified (2S, 3R)-2-((Z)-oct-2′-enyl)-3-nonyl oxirane (hereafter Z6-9S, 10R-epoxy-19:H) as the female-produced sex pheromone. Significantly more male moths were captured between 1–100 μg loadings of this compound on red rubber septa in sticky traps compared to blank (unbaited) traps; catches then declined at higher dosages (500–1000 μg). The other isomeric enantiomer, (2R, 3S)-2-[(Z)-oct-2′-enyl]-3-nonyl oxirane (Z6-9R, 10S-epoxy-19:H), at a 10-μg dosage did not elicit trap capture. The likely precursor to the active epoxide, (Z, Z)-6, 9-nonadecadiene ((Z, Z)-6, 9-19:H), identified in virgin female sex pheromone glands, did not elicit trap capture either, and inhibited trap capture when combined with the active epoxide. Racemic 2-((Z)-oct-2′-enyl)-3-nonyl oxirane showed no significant difference in trap capture compared with Z6-9S, 10R-epoxy-19:H, indicating that the opposite enantiomer was not antagonistic. The addition of the EAD-active diene epoxide enantiomers (2S, 3R)-2-[(Z, Z)-octa-2′, 5′-dienyl]-3-nonyl oxirane or (2R, 3S)-2-[(Z, Z)-octa-2′, 5′-dienyl]-3-nonyl oxirane in admixture with Z6-9S, 10R-epoxy-19:H (at 10% of the latter) did not enhance or decrease trap capture compared to Z6-9S, 10R-epoxy-19:H oxirane alone, so they are not likely pheromone components. This pheromone, impregnated in rubber septa at less than 100-μg dosage, can now be used as a trap bait to develop detection and monitoring strategies for this insect.
KeywordsGeometridae Ennominae Ennomos subsignaria Sex pheromone Alkenyl epoxide (2S, 3R)-2-((Z)-oct-2′-enyl)-3-nonyl oxirane Trapping
We thank Gaetan LeClair, Andrea Sharpe, Catherine Desjardins, and Heidi Fry for their technical assistance. We also thank Laura and Julia Coombes for their invaluable help in conducting the field test in Newfoundland in the summer of 2009. A special thanks to Peggy Dixon (Agriculture and Agri-Food Canada, NL) for her coordination efforts in 2009. Funding support was from Natural Resources Canada, Canadian Forest Service, and Ontario Natural Resources through SERG International. J W wishes to thank University of New Brunswick for a scholarship in the Masters program in Chemistry. We thank Jocelyn Millar (University of California Riverside) and Ashot Khrimian (United States Department of Agriculture) for the gift of several epoxide compounds as analytical standards during the exploratory stage of this study. All experiments reported here comply with the laws of Canada.
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