Data from: Colonization of weakened trees by mass-attacking bark beetles: no penalty for pioneers, scattered initial distributions and final regular patterns

Bark beetles use aggregation pheromones to promote group foraging, thus increasing the chances of an individual to find a host and, when relevant, to overwhelm the defences of healthy trees. When a male beetle finds a suitable host, it releases pheromones that attract potential mates as well as other "spying" males, which results in aggregations on the new host. To date, most studies have been concerned with the use of aggregation pheromones by bark beetles to overcome the defences of living, well-protected trees. How insects behave when facing undefended or poorly defended hosts remains largely unknown. The spatio-temporal pattern of resource colonization by the European eight-toothed spruce bark beetle, Ips typographus, was quantified when weakly defended hosts (fallen trees) were attacked. In many of the replicates, colonization began with the insects rapidly scattering over the available surface and then randomly filling the gaps until a regular distribution was established, which resulted in a constant decrease in nearest-neighbour distances to a minimum below which attacks were not initiated. The scattered distribution of the first attacks suggested that the trees were only weakly defended. A minimal theoretical distance of 2.5 cm to the earlier settlers (corresponding to a density of 3.13 attacks/dm²) was calculated, but the attack density always remained lower, between 0.4 and 1.2 holes/dm², according to our observations.

树皮甲虫（bark beetles）会借助聚集信息素（aggregation pheromones）开展群体觅食，以此提升个体找到寄主的概率，且在适宜情境下可协同突破健康树木的防御体系。当雄性甲虫发现适宜寄主后，会释放信息素吸引潜在配偶，同时也会吸引其他“侦察”雄性，最终在新寄主上形成聚集种群。迄今为止，多数相关研究聚焦于树皮甲虫利用聚集信息素突破健康、防御完善的树木的防御机制，而昆虫在面对未设防或防御薄弱的寄主时的行为模式，目前仍鲜为人知。本研究针对防御薄弱的寄主（倒伏木）被攻击的场景，量化了欧洲云杉八齿小蠹（Ips typographus）对资源的时空定植模式。在多数重复实验中，定植过程首先表现为昆虫快速扩散至寄主的可利用表面，随后随机填补空隙，直至形成规则分布格局；此过程伴随最近邻距离持续缩短，当距离降至某一临界值后，便不再发起新的攻击。首次攻击呈现的分散分布格局，表明该树木仅具备薄弱防御能力。经计算，早期定植个体间的理论最小距离为2.5厘米（对应攻击密度为3.13次/平方分米），但观测结果显示实际攻击密度始终更低，介于0.4至1.2个蛀孔/平方分米之间。