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 by 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 (e.g., Dendroctonus
frontalis and D. barberi) avoid phloem infested with non-mycangial fungi
such as Ophiostoma minus, while secondary beetles like Ips pini, 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 compounds as repellents.

树皮甲虫是重要的森林害虫，主要致树死亡的种类常依赖于由特化真菌囊（mycangia）携带的专性共生真菌。相比之下，次级树皮甲虫通常不攻击健康树木，且常缺乏专性真菌共生体。然而，所有树皮甲虫均会传播真菌，这些真菌可能为其提供营养、改善基质条件，或作为拮抗剂阻碍其生存繁殖。本研究引入一种配对管选择测试装置，以使用最少的韧皮部培养基评估树皮甲虫与真菌的相互作用。我们假设，携带真菌囊真菌的初级树皮甲虫（如额毛小蠹Dendroctonus frontalis和D. barberi）会避开被非真菌囊真菌（如Ophiostoma minus）侵染的韧皮部，而不依赖真菌囊真菌的次级甲虫（如Ips pini）则对真菌侵染或无真菌的韧皮部无偏好。研究结果显示，D. barberi偏好未受侵染的韧皮部，而Ips pini则偏好被Ophiostoma minus侵染的韧皮部。有趣的是，额毛小蠹Dendroctonus frontalis对未受侵染或被Ophiostoma minus侵染的韧皮部均无偏好。这些结果强调了理解真菌共生体对树皮甲虫钻蛀行为影响的重要性，其在害虫管理中具有潜在应用价值，例如利用拮抗真菌化合物的信号作为驱避剂。