# Effect of Volatile Organic Compounds from Branches of Healthy and Unhealthy Araucaria araucana (Molina) K. Koch Trees on Host Selection by Bark Beetle Sinophloeus porteri (Coleoptera: Curculionidae)

## TL;DR

This study shows that bark beetles prefer the scent of unhealthy ancient Chilean trees, which could help explain how these beetles contribute to tree damage.

## Contribution

The study identifies specific volatile compounds from Araucaria araucana that attract or repel bark beetles, providing new insights into tree-insect interactions.

## Key findings

- Myrcene from healthy Araucaria branches repels S. porteri beetles.
- Hibaene from unhealthy branches attracts S. porteri beetles.
- Beetles prefer volatile blends from unhealthy trees over healthy ones.

## Abstract

Araucaria araucana is one of the oldest trees in Chile, with a lifespan of up to 1000 years. Recently, a disease known as Araucaria Leaf Damage (ALD) has been affecting these trees, causing damage to their branches and crowns. Bark beetles, including Sinophleous porteri, may contribute to this problem, either by directly damaging the trees or by spreading harmful fungi. However, little is known about how these insects interact with these trees. This study examines whether volatile organic compounds released by the trees affect the behavior of S. porteri. We collected branches and beetles from a national park and analyzed the chemical compounds released by healthy and unhealthy trees. Myrcene, the most abundant compound emanated by healthy branches, was repellent to this weevil. Hibaene, found in high amounts in unhealthy branches, was attractive to S. porteri beetles. These findings help us understand how beetles respond to tree cues and may inform future strategies for monitoring and protecting these ancient trees. Understanding these interactions is crucial to conserving A. araucana, especially as environmental changes threaten its survival.

Araucaria araucana is one of the longest-living Chilean trees. Recently, Araucaria Leaf Damage disease, which causes damage to branches and crowns, was detected. Sinophloeus porteri, a bark beetle affecting A. araucana, could be associated with foliar damage. However, little is known about their ecological and chemical interactions. This study examined the olfactory response of S. porteri to volatiles emitted from A. araucana. Branches and weevils were collected from a national park, and volatiles were trapped from both healthy and unhealthy branches. Thirty terpenes were identified, some of which were reported for the first time in A. araucana. Healthy branches emitted large amounts of myrcene (>360 ng g−1 day−1), and unhealthy branches showed high hibaene emanations (>140 ng g−1 day−1). Olfactory assays verified that S. porteri was attracted to the volatile blends of branches, regardless of the health condition of the branches, but preferred the blend of unhealthy branches. Moreover, myrcene was repellent to these weevils, and hibaene acted as an attractant, suggesting that A. araucana might use myrcene for defense against S. porteri, and hibaene could stimulate host selection by beetles.