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.

树皮甲虫通过释放聚集信息素（aggregation pheromones）促进群体觅食，以此提升个体找到寄主的概率，必要时还可协同击溃健康树木的防御系统。当雄性甲虫找到适宜寄主后，会释放信息素吸引潜在配偶，同时也会吸引其他“窥探”的雄性个体，最终在新寄主上形成聚集群体。迄今为止，多数研究聚焦于树皮甲虫利用聚集信息素突破存活且防御完备的树木的防御机制，而昆虫面对未受防御或防御薄弱的寄主时的行为模式，目前仍鲜为人知。本研究针对欧洲八齿云杉树皮甲虫（Ips typographus）在攻击防御薄弱寄主（枯倒木）时的资源定植时空格局展开定量分析。在多数重复实验中，定植过程始于昆虫快速扩散至寄主表面，随后随机填补空隙，直至形成均匀分布格局；此过程中最近邻个体距离持续缩短至临界最小值，低于该距离则不会发起新的攻击。首批攻击的随机分散分布表明，该树木仅具备微弱防御能力。研究计算得出，与先期定居者的最小理论距离为2.5厘米（对应定植密度为3.13次攻击/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个孔洞/平方分米之间。