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）会利用聚集信息素（aggregation pheromones）推动群体觅食行为，以此提升个体找到寄主的概率，在适宜条件下还能协同击溃健康树木的防御体系。当雄性甲虫找到合适寄主后，会释放信息素吸引潜在配偶，同时也会引来其他"侦察"雄性，最终在新寄主上形成聚集群体。迄今为止，绝大多数相关研究均聚焦于树皮甲虫利用聚集信息素抵御活的、防御完备的树木的相关机制。而当昆虫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（倒木）被侵染的场景，量化了欧洲八齿云杉树皮甲虫（Ips typographus）对资源的时空定植模式。在多数重复实验中，侵染过程始于昆虫快速扩散至可用寄主表面，随后随机填补空隙，直至形成均匀分布的群体；此过程中个体间的最近邻距离持续缩短，直至达到临界最小值，当距离低于该值时便不再发起新的攻击。首批攻击呈现出的分散分布特征，表明该寄主树木仅具备微弱防御能力。研究计算得出，与先期定植个体的最小理论距离为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。