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)

Abstract

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.

Keywords: Araucaria araucana; Sinophloeus porteri; olfactometry; volatile organic compounds (VOCs).

Figure 1

(Left) Heat map, including a dendrogram, showing the relative abundance of the 30 compounds present in volatiles from branches of healthy and unhealthy trees, from blue color (low abundance) to red color (high abundance). (Right) Exploratory principal component analysis (PCA): score plot and loading plot of the first two principal components for 30 terpenes from healthy and unhealthy branches.

Figure 2

Olfactory response of S. porteri beetles exposed to volatile blends of A. araucana from (A) healthy branches, (B) unhealthy branches, and (C) healthy and unhealthy branches. ZD: zone of decision. The lines on the bars indicate the standard error. Different letters indicate significant differences based on one-way ANOVA and the HSD Tukey test (p ≤ 0.05), n = 30.

Figure 3

Olfactory response of S. porteri beetles exposed to single compounds identified in the volatile blends of branches, diluted in n-hexane. (A) Myrcene, (B) hibaene, (C) camphor, (D) α-pinene, and (E) limonene. Blank: hexane; ZD: zone of decision. The lines on the bars indicate the standard error. Different letters indicate significant differences based on one-way ANOVA and the HSD Tukey test (p ≤ 0.05), n = 30.