A guest post by OPB’s environment reporter Rob Manning
A recurring western environmental mystery is back this summer.
They’re called “white pine” or “pine white” butterflies, and carry the scientific name, Neophasia menapia. The butterflies feed on ponderosa pine needles and can substantially defoliate trees. But Forest Service entomologist Don Scott says the trees don’t usually die as a result.
The butterflies are native to ponderosa pine forests across the West. But scientists say every thirty or forty years or so, there are huge outbreaks of the butterflies.
Entomologist, Don Scott, says it’s not clear what causes the outbreaks.
“It seems weather or climate-related,” Scott says. But he says there’s no better explanation than that.
Scott says this latest outbreak started in 2009. Before that, scientists know of similar ones in the 1900s, the 1940s, and the 1980s.
While the cause of the outbreaks is up for debate, Scott says there’s a better sense of what ends them.
Scott says the butterflies wind up eating up so much of their food source – ponderosa pine needles - that there’s not enough to support subsequent generations. In addition, the butterflies have predators, like wasps and a member of the stinkbug family. They adjust to the bigger butterfly populations by increasingly targeting their pupae and larvae.
Scott expects the most recent outbreak is peaking this summer. He predicts the outbreak will decline next summer, and the butterfly’s numbers will be down substantially, by 2013.