Data from: Geosmithia associated with bark beetles and woodborers in the western USA: taxonomic diversity and vector specificity

Fungi in the genus Geosmithia (Ascomycota: Hypocreales) are frequent associates of bark beetles and woodborers that colonize hardwood and coniferous trees. One species, Geosmithia morbida, is an economically damaging invasive species. The authors surveyed the Geosmithia species of California and Colorado, USA, to (i) provide baseline data on taxonomy of Geosmithia and beetle vector specificity across the western USA; (ii) investigate the subcortical beetle fauna for alternative vectors of the invasive G. morbida; and (iii) interpret the community composition of this region within the emerging global biogeography of Geosmithia. Geosmithia was detected in 87% of 126 beetle samples obtained from 39 plant species. Twenty-nine species of Geosmithia were distinguished, of which 13 may be new species. Bark beetles from hardwoods, Cupressus, and Sequoia appear to be regular vectors, with Geosmithia present in all beetle gallery systems examined. Other subcortical insects appear to vector Geosmithia at lower frequencies. Overall, most Geosmithia have a distinct level of vector specificity (mostly high, sometimes low) enabling their separation to generalists and specialists. Plant pathogenic Geosmithia morbida was not found in association with any other beetle besides Pityophthorus juglandis. However, four additional Geosmithia species were found in P. juglandis galleries. When integrated with recent data from other continents, a global pattern of Geosmithia distribution across continents, latitudes, and vectors is emerging: of the 29 Geosmithia species found in the western USA, 12 have not been reported outside of the USA. The most frequently encountered species with the widest global distribution also had the broadest range of beetle vectors. Several Geosmithia spp. with very narrow vector ranges in Europe exhibited the similar degree of specialization in the USA. Such strong canalization in association could reflect an ancient origin of each individual association, or a recent origin and a subsequent diversification in North America.

帚丝霉属（Geosmithia，子囊菌门：肉座菌目）的真菌，常与蛀食阔叶树与针叶树的树皮甲虫、蛀木甲虫形成稳定共生关系。其中物种胡桃帚丝霉（Geosmithia morbida）是具有重大经济危害的入侵性真菌。本研究团队对美国加利福尼亚州与科罗拉多州的帚丝霉属物种开展了系统性调查，旨在达成三项研究目标：（1）为美国西部全域的帚丝霉属分类学研究以及甲虫媒介特异性提供基础数据；（2）调查皮层下甲虫类群，以明确入侵性胡桃帚丝霉（G. morbida）的潜在替代媒介；（3）结合当前帚丝霉属全球生物地理学研究的最新进展，阐释该区域的真菌群落组成特征。

研究从39种植物中采集了126份甲虫样本，其中87%的样本中检测到了帚丝霉属真菌。共鉴定出29种帚丝霉属真菌，其中13种可能为新物种。取自阔叶树、柏木属（Cupressus）以及红杉属（Sequoia）的树皮甲虫，似乎是帚丝霉属真菌的常规媒介，所有被检测的甲虫坑道系统中均存在该属真菌。其他皮层栖居昆虫作为帚丝霉属媒介的传播频率相对较低。

总体而言，多数帚丝霉属真菌表现出程度各异的媒介特异性——多数为高特异性，少数为低特异性——据此可将其划分为泛化型共生真菌与特化型共生真菌。作为植物病原菌的胡桃帚丝霉（G. morbida），仅与黑胡桃小蠹（Pityophthorus juglandis）形成共生关联，未在其他任何甲虫类群中检出。但在黑胡桃小蠹的坑道系统中，还发现了另外4种帚丝霉属真菌。

结合其他大洲的最新研究数据，帚丝霉属真菌在全球各大洲、不同纬度以及不同媒介类群间的分布模式正逐渐明晰：在美国西部检出的29种帚丝霉属真菌中，有12种尚未在美国以外的地区被报道过。全球分布范围最广、检出频率最高的帚丝霉属物种，其可关联的甲虫媒介类群也最为多样。在欧洲表现出极窄媒介范围的数种帚丝霉属真菌，在美国也呈现出相似的特化程度。这种高度专一的共生关联模式，既可能源于各共生关系的古老起源，也可能是北美地区近期起源并随后发生适应性分化的结果。