Insect-Associated Fungi and Blue Stain Fungi

Bark beetles, horntails, ambrosia beetles

Ophiostoma, Raffaelea, Leptographium and others

Ophiostoma species are common associates of bark beetles (Harrington, 1993a, 1993b, 2005, Paine et al. 1997), but they are also important as stain fungi. Much of the blue stain in conifer timber is caused by species of Ophiostoma and their anamorphs, especially Graphium and Leptographium.

A study on the Ophiostoma piceae complex was completed (Harrington et al. 2001), and a manuscript on the Ophiostoma species found in New Zealand was published (Thwaites et al. 2005).

We (Six et al. 2003) also looked at the genetically similar but morphologically distinct Leptographium terebrantis, which is associated with a number of pine bark beetles, and its more insect-specialized relatives Ophiostoma clavigerum and L. pyrinum.

The evolution of basidiomycetes associated with bark beetles was recently examined (Hsiau and Harrington 2003), and a review of the evolution and ecology of mycophagus bark beetles and their fungal symbionts has just been published (Harrington 2005).

We also studied the Amylostereum species associated with horntails (Tabata et al. 2000).

Graduate student Sujin Kim studied insects associated with two introduced beetles in California (Kim et al. 2011).


Laurel wilt, caused by Raffaelea lauricola

Another on-going study is the new laurel wilt pathogen that was introduced with the Asian ambrosia beetle, Xyleborus glabratus, to the Coastal Plains of the southeastern USA. This work is conducted with Stephen Fraedrich and others (Fraedrich et al., 2008; Harrington et al. 2008; Harrington et al., 2010; Harrington and Fraedrich, 2010; Fraedrich et al., 2011; Harrington et al., 2011). I have a separate page on my work on with laurel wilt, and the Laurel Wilt Task Force has much more information.

Click here for a listing of all publications on Ophiostoma, Leptographium and insect-associated Fungi

From generalist bark beetle associate:

 

FIGS. 1­9. Leptographium pyrinum and L. terebrantis. 1­3. L. pyrinum. 1, 2. Conidiophores. 3. Conidia. 1­3 from strain C833. 4­9. L. terebrantis. 4, 5. Conidiophores. 6. Conidia. 7, 8. Conidiophores. 9. Conidia. 4­6 from strain C680. 7­9 from strain C25. Scale bars: 1 = 100 µm; 2, 7 = 50 µm; 3, 6, 9 = 10 µm; 4, 5, 8 = 25 µm  

Compare the morphology of these genetically related species, especially the long, clavate conidia of Ophiostoma clavigerum (Figs. 10-16), which appear to be more suitable for grazing by its bark beetle symbionts (Dendroctonus ponderosae and D. jeffreyi), which are mycophagus for at least part of their life cycle. We believe O. clavigeum evolved from a more generalist species, perhaps Leptographium terebrantis (Figs. 4-9), which has been associated with many unrelated bark beetle species. Note that cultures of O. clavigerum can degenerate and form conidia and conidiophores (Figs. 13-16) more typical of L. terebrantis.

Six et al. 2003

To ambrosia for mycophagus bark beetles:

FIGS. 10­16. Ophiostoma clavigerum. 10, 11. Conidiophores. 12. Clavate conidia. 13, 14. Conidiophores. 15. Clavate conidia. 16. Conidia. 10­12 from strain C187. 13­16 from strain C813. Scale bars: 10, 13 = 50 µm; 11, 14, 15 = 25 µm.