Geosmithiaassociated with bark beetles and woodborers in the western USA: taxonomic diversity and vector specificity

Abstract

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.

Geosmithia species associated with fir-infesting beetles in Poland

“…The European silver fir weevil (P. piceae) and the striped ambrosia beetle (T. lineatum) were not associated with Geosmithia in our study. Similar results have recently been reported from the Western USA [11]. According to a study conducted by Kolařík et al [11], Geosmithia spp.…”

“…where adults do not enter these tissues. Although, there are many studies confirming associations between ambrosia beetles and Geosmithia fungi [8,10,11,14,16], our study showed that T. lineatum does not transmit Geosmithia. There was also no evidence that this ambrosia beetle can transmit Geosmithia fungi in pine habitats [9].…”

“…Members of the Hypocreales are common in all types of moist forests [3], however, only Geosmithia fungi that produce Penicillium-like conidiophores are associates of bark beetles on hardwood and conifer trees worldwide [4][5][6][7][8][9][10][11][12][13][14][15][16]. The bark beetle-Geosmithia relationships vary, ranging from specialists with a limited range of vectors to generalists recorded with numerous vectors [4,6,9,11]. On Pinaceae, the typical vectors of Geosmithia are bark beetles infesting Pinus sylvestris L. The pineassociated Geosmithia are a group of specialists living only on the Pinaceae [9,12,17].…”

Detection of Geosmithia morbida on Numerous Insect Species in Four Eastern States

“…We were unable to devise a primer pair using the ITS region that was specific enough to detect G. morbida alone (unpublished results). This is consistent with other researchers' observations that the ITS region is not sufficiently informative to distinguish certain Geosmithia species (Kolařík et al 2017). An 86% accuracy level for detection of G. morbida was determined for this protocol based on DNA sequencing results.…”

Host selection behavior mediated by differential landing rates of the walnut twig beetle, Pityophthorus juglandis, and associated subcortical insect species, on two western North American walnut species, Juglans californica and J. major

“…Pityophthorus juglandis (Bright, 1981) and G. morbida (Kolařík et al, 2011; Tisserat et al, 2011) were first collected and described from populations in the western USA, and since 2010, they have also spread to the eastern USA (Seybold et al, 2013a, 2016). Surveys in the western USA suggest that P. juglandis may be the only subcortical insect to carry G. morbida (Kolařík et al, 2017). There have been reports from the eastern USA that other subcortical insects may vector G. morbida in walnut, but the phoresy rates have been low, transmission has not been demonstrated experimentally, and the insects were mostly species that target moribund trees (Juzwik et al, 2015).…”