This week, The Scientist reports on a study suggesting the long-cherished mistletoe may be messing with the white spruce trees’ hormones. In a not-yet-published report, Barry Logan, an associate professor of biology at Bowdoin College, and his team discovered that, unlike traditional host-parasite relations where, in an attempt to stave off damage, the host tree directs water and nutrients to healthy limbs and branches at the expense of infected ones, the dwarf mistletoe triggers the white spruce to manufacture hormones that direct cherished resources towards infected branches. The parasitic effects of the dwarf mistletoe include tangled witches’ brooms , small needles and stunted tree growth.
Dwarf mistletoe isn’t always lethal, according to The Scientist.
“Forty-two species (including the eastern variety) exist, and they impart varying degrees of harm on their favorite host trees. In Washington and Oregon, western hemlocks show evidence of having weathered infections of hemlock dwarf mistletoe for 80 years or more, Logan says. White spruce, on the other hand, succumb to eastern dwarf mistletoe in 15 or 20 years.”
“There’s an interplay between [host and parasite] which I didn’t appreciate when I first tackled this project,” Logan adds. “It makes it more interesting, and more complicated.”