A novel choice test to detect the influence of fungi on the tunneling behavior of sympatric bark beetles (Coleoptera: Scolytinae)

Bark beetles are significant forest pests, with primary tree-killing species often relying on obligate mutualistic fungi carried in specialized mycangia. In contrast, secondary bark beetles, which do not typically attack healthy trees, often lack obligate fungal mutualists. However, all bark beetles vector fungi that may provide nutrition to them, improve substrate conditions, or act as antagonists, hindering their success. This study introduces a paired-tube choice test arena to assess bark beetle–fungal interactions using minimal phloem-media. We hypothesized that primary bark beetles with mycangial fungi (eg Dendroctonus frontalis Zimmermann and Dendroctonus barberi Hopkins) avoid phloem infested with nonmycangial fungi such as Ophiostoma minus (Hedgcock) Sydow & P. Sydow, while secondary beetles like Ips pini Say, which do not rely on mycangial fungi, show no preference for fungal-infested or fungus-free phloem. Our findings revealed that D. barberi preferred uninfested phloem, whereas I. pini preferred the O. minus-infested phloem. Interestingly, D. frontalis did not show a preference for either uninfested phloem or O. minus-infested phloem. These results underscore the importance of understanding the effects of fungal symbionts on tunneling behavior, with potential applications in pest management, such as deploying cues from antagonistic fungi as repellents.