Navigating the Semiochemical Landscape: Attraction of Subcortical Beetle Communities to Bark Beetle Pheromones, Fungal and Host Tree Volatiles

Abstract

Subcortical beetle communities interact with a wide range of semiochemicals released from different sources, including trees, fungi, and bark beetle pheromones. While the attraction of bark beetles, their insect predators, and competitors to bark beetle pheromones is commonly studied, the attraction of these beetle communities to other sources of semiochemicals remains poorly understood. We tested the attraction of bark and wood-boring beetles and their predators to host stress volatiles, fungal volatiles, and a mountain pine beetle lure in the field. Host stress volatiles were derived from lodgepole pine trees stressed by three fungal symbionts of mountain pine beetle and two common phytopathogens. Our results showed that bark beetles, particularly mountain pine beetles, show a preference for a combination of fungal volatiles, particularly 2-methyl-1-butanol and its lures. Without the addition of lures, 2-methyl-1-butanol was also identified as a key fungal volatile in the attraction of mountain pine beetle competitors from the Cerambycidae and Buprestidae families. Predators in the Elateridae and Staphylinidae families showed attraction to host stress volatiles and the healthy tree volatile profiles. These findings suggest that these semiochemicals warrant further field testing for potential use in monitoring and management of subcortical beetle populations.

Keywords: Atropellis piniphila; Buprestidae; Cerambycidae; Elateridae; Endocronartium harknessii; Grosmannia clavigera; Leptographium longiclavatum; Ophiostoma montium; Staphylinidae; forest health; volatile organic compounds (VOCs).

Figure 1

Experimental field site and trap setup. B1, B2, and B3 represent the three blocks of traps for each experiment, and arrows indicate the direction of trap rotation after each collection. (a) Location of sites within British Columbia. (b) Trap locations at field site 1; fungal volatiles (FVOCs) combined with pheromone experiment. (c) Trap locations at field site 2; FVOC-alone treatments (stars) and host stress volatiles (SVCs)-alone treatments (circles) were placed at this site. (d) Beetle traps used in our experiments: a flight intercept trap, used in our FVOC experiments (left) and a Lindgren funnel trap, used for the SVC experiment (right).

Figure 2

Mean catches of each subcortical beetle group throughout the collection period. Mean catches were calculated using data from all volatile groups. Traps were collected weekly for 5 weeks from 13 July (Collection 1) to 10 August (Collection 5). Catches from collection 2 are excluded due to the loss of traps during an extreme wind event between collections. Error bars represent standard error. Kruskal–Wallis tests were run for significant differences between collections at p < 0.05. Note: y-axes are on different scales due to large variations in catches between each subcortical beetle group. Collections with the same letter within each beetle group are not significantly different; Dunn’s test with Bonferroni’s adjustment at p < 0.05.

Figure 3

Non-metric Multidimensional Scaling (NMDS) plot showing the differences in subcortical beetle community composition between volatile treatment groups. Subcortical beetle catches over the entire field season were analyzed using an NMDS gradient analysis. Bray–Curtis was used as the distance metric. The vectors (black arrows) correspond to the five groups of subcortical beetles included in the analysis. The ellipses represent 95% confidence intervals around the centroid of each volatile treatment group. Volatile groups include (1) fungal volatiles combined with mountain pine beetle (MPB) pheromone lures (FVOCP), (2) fungal volatiles alone (FVOC), (3) host stress volatile chemical profiles associated with fungi (SVC), (4) healthy lodgepole pine volatile profile (Healthy), (5) MPB pheromone lures alone (Pheromone), (6) mineral oil alone (Control). Stress = 0.151, indicating goodness of fit for the ordination. Significant differences between volatile groups were determined by PERMANOVA using Bray–Curtis dissimilarity (at p < 0.05).

Figure 4

Trends in percent relative catches of subcortical beetle families between volatile treatment groups. Volatile treatment groups include: (1) fungal volatiles combined with mountain pine beetle (MPB) pheromone lures (FVOCP), (2) fungal volatiles alone (FVOC), (3) host stress volatile chemical profiles (SVC), (4) healthy lodgepole pine volatile profile (Healthy), (5) MPB pheromone lures alone (Pheromone), (6) mineral oil alone (Control). Note: the y-axis for (a) Scolytinae is on a different scale due to larger relative catches in one volatile treatment group compared to other subcortical beetle families.