Studies on transmission of blue-stain fungi by Ips pini
Ips pini (EPPO A1 quarantine pest) is one of the most widely distributed bark beetles in North America. In Idaho, it kills Pinus ponderosa and P. contorta. Blue-stain fungi which can be tree-pathogenic are often found in association with Dendroctonus and Ips species, as they enable bark beetles to colonize live conifers successfully by overcoming their defence. A blue-stain fungus, Ophiostoma ips is found in association with Ips pini in California, Massachusetts, Minnesota*, Wisconsin* and Ontario. This fungus, which is pathogenic to pines, probably occurs throughout the range of Ips pini and is also reported in association with other Ips species, including Ips calligraphus in Florida, North Carolina, Maryland* and New Jersey*, Ips grandicollis in Florida, Ips lecontei in Arizona. Other blue-stain fungi reported in association with Ips pini are Ophiostoma nigrocarpum in Wisconsin, O. huntii in British Columbia and Colorado, and Ambrosiella ips in Minnesota.
Studies have been carried out on the transmission of O. ips by I. pini. By using electron microscopy, it was shown that strial pits on the elytra of I. pini carry spores like those of O. ips, yeast and other fungi. O. ips ascospores develop on the walls of pupal chambers in the phloem of infested pines and adhere to newly transformed I. pini adults. Inoculation of severed pine stem sections with body parts excised from beetles washed in water or alcohol produced phloem lesions characteristic of the hypersensitive wound reaction to O. ips. The fungi could be then reisolated from wood beneath the inoculation lesions. Similar studies have been carried out on live trees, inoculation with an elytron-derived culture of the fungi caused necrosis of sapwood (radially inward from lesions), and tree mortality when lesions encircled the stem (spacing between lesions ;1 cm).
____________
* New detailed records.
Sources
Furniss, M.M.; Harvey, A.E.; Solheim, H. (1995) Transmission of Ophiostoma ips (Ophiostomatales: Ophiostomataceae) by Ips pini (Coleoptera: Scolytidae) to Ponderosa pine in Idaho.
Annals of the Entomological Society of America, 88(5), 653-660.