Red turpentine beetle primary attraction to (–)-β-pinene+ethanol in US Pacific Northwest ponderosa pine forests

Abstract

Red turpentine beetle, Dendroctonus valens (Coleoptera: Curculionidae: Scolytinae) is a non-aggressive pine bark beetle native to North America, and more aggressive invader in China. Dispersing pioneer beetles are attracted to potential host trees by oleoresin monoterpene kairomones, but respond more strongly to those combined with ethanol, a mixture often released from stressed, dying, or recently dead trees. (+)-3-Carene, usually the dominant or co-dominant monoterpene in ponderosa pine, Pinus ponderosa, is a stronger attractant than α-pinene or β-pinene where tested over a large portion of the D. valens range, while (+)-3-carene+ethanol was shown previously to attract twice the beetles of (+)-3-carene. A field test comparing D. valens attraction among the three monoterpenes when all are released with ethanol has never been reported, and was our objective. In three US Pacific Northwestern pine forests, (-)-β-pinene+ethanol lures attracted 1.4 to 1.9 times more beetles than (+)-3-carene+ethanol. (+)-or (±)-α-pinene+ethanol lures were least attractive. A 1:1:1 monoterpene mixture+ethanol lure attracted more beetles than the 1:1:1 lure, but it was not statistically higher. Monoterpenes were dispensed from low density polyethylene bottles and their release rates monitored in laboratory and field tests. Under laboratory conditions (+)-3-carene was released much more rapidly than (+)-α-pinene or (-)-β-pinene when dispensed separately, or in a 1:1:1 mixture. (+)-3-Carene in the 1:1:1 mixture increased the release of both pinenes over their rates when dispensed separately. (-)-β-Pinene+ethanol is currently the strongest kairomone lure for D. valens attraction in US northwest pine forests, and has value for beetle detection, monitoring, research, and management.

Red turpentine beetle primary attraction increases linearly with (−)‐β‐pinene+ethanol dose regardless of component ratios, and no change in response with addition of high‐release frontalin

“…Combining high‐release (±) frontalin with monoterpene+ethanol lures had minimal impact on the D. valens response since β‐pinene+ethanol+frontalin and β‐pinene+ethanol attracted similar beetle numbers. Furthermore, the order and levels of attraction for the three different monoterpene+ethanol+frontalin lures observed here were comparable to the monoterpene+ethanol lures in Washington and Oregon field trials (Kelsey & Westlind, 2020). Here, the β‐pinene+ethanol+frontalin catch was 1.9 times greater than 3‐carene+ethanol+ frontalin, and the latter was 1.6 times greater than α‐pinene+ethanol+frontalin.…”

“…(+)‐3‐Carene (> 90.0%), (+)‐α‐pinene (97%) and (−)‐β‐pinene (≥ 97%) were obtained from Sigma Aldrich (St. Louis, Missouri) and dispensed from low‐density polyethylene (LDPE) bottles (15 mL, The Cary Company, Addison, Illinois) filled to the threaded neck, leaving a small air bubble under the cap. Bottles were filled in advance and held a minimum of 5 days at room temperature to saturate the plastic (Kelsey & Westlind, 2020). One day prior to field placement they were refilled, weighed and immediately moved to a 5 °C cold room for several hours until further processed.…”

“…Lure mixing jars used here were smaller (9.3 × 9.7 cm, D × L cap on, 473 mL), with five equally spaced ventilation holes drilled into the bottom (0.79 cm diameter) and into the screw cap (0.95 cm diameter) in an X pattern (Kelsey & Westlind, 2020, 2021). A screen inside the cap prevented insects from entering the top holes, and the outside jar wall was wrapped with aluminium foil to reduce solar heating.…”

“…A screen inside the cap prevented insects from entering the top holes, and the outside jar wall was wrapped with aluminium foil to reduce solar heating. Each jar received one ethanol pouch wrapped around the inside wall leaving a center opening for one 3‐carene bottle, or two α‐pinene, or two β‐pinene bottles to provide similar release rates based on laboratory tests (Kelsey & Westlind, 2020). One ibutton temperature data logger was placed into a randomly selected lure jar from each block to record temperatures.…”

“…(+)‐3‐Carene lures attract D. valens in Oregon, but combining it with ethanol produced a synergistic response, catching two times more beetles than (+)‐3‐carene, and four times more than ethanol (Kelsey & Westlind, 2017c). However, in Washington and Oregon, (−)‐β‐pinene+ethanol lures attracted 1.4–1.9 times more beetles than (+)‐3‐carene+ethanol, depending on the site, and (+)‐α‐pinene+ethanol or (±)‐α‐pinene+ethanol lures were least attractive at all sites where tested (Kelsey & Westlind, 2020). The exocyclic double bond in (−)‐β‐pinene is a key structural feature contributing to its stronger primary attraction over (+)‐3‐carene and (+)‐α‐pinene when ethanol is present (Kelsey & Westlind, 2021).…”