Key structural features in cis‐carane, (+)‐3‐carene, cis‐pinane, (+)‐α‐pinene, and (−)‐β‐pinene influencing red turpentine beetle primary attraction when released with ethanol

• Published in: Agricultural and forest entomology Vol. 23; no. 3; pp. 243 - 249
• Main Authors: Kelsey, Rick G., Westlind, Douglas J.
• Format: Journal Article
• Language: English
• Published: Oxford, UK Blackwell Publishing Ltd 01.08.2021
• Subjects: (−)‐β‐pinene; Attraction; Beetles; Carbon; cis‐carane; cis‐pinane; Coniferous forests; Dendroctonus valens; Ethanol; Field tests; Isomers; Monoterpenes; Pine trees; primary attraction; Turpentine; α-Pinene
• ISSN: 1461-9555; 1461-9563
• DOI: 10.1111/afe.12426

In US Pacific Northwest ponderosa pine forests the primary attraction order shown previously for red turpentine beetle, Dendroctonus valens (Coleoptera: Curculionidae: Scolytinae), is (−)‐β‐pinene+ethanol > (+)‐3‐carene+ethanol > (+)‐α‐pinene+ethanol. The monoterpenes are bicyclic C10H16 isomers containing one 6‐carbon ring with one double bond. Both pinenes have a 4‐carbon second ring and differ only by their endocyclic or exocyclic double bond. The (+)‐3‐carene second ring has 3‐carbons; its double bond is endocyclic like (+)‐α‐pinene. Ring system and double bond influences on primary attraction were evaluated by hydrogenating (+)‐3‐carene and (+)‐α‐pinene to cis‐carane and cis‐pinane, respectively. Field test primary attraction strengths were (−)‐β‐pinene+ethanol > cis‐carane+ethanol > cis‐pinane+ethanol > ethanol. In combination with ethanol (i) a double bond is not required in either ring system to attract D. valens, (ii) the cis‐carane bicyclic 3, 6‐carbon ring system provides stronger beetle attraction than the cis‐pinane 4, 6‐carbon bicyclic ring system, and likely structural basis for stronger (+)‐3‐carene attraction over (+)‐α‐pinene, (iii) adding an exocyclic double bond to the 4, 6‐carbon ring system elevates attraction above the 3, 6‐carbon ring system with no double bond, and (iv) the 4, 6‐carbon ring system is a much stronger attractant with an exocyclic rather than endocyclic double bond.