Montana’s weed-control fly was linked to 3x more hantavirus-positive mice
A 1973 biological control project in Montana intended to curb invasive knapweed inadvertently increased the population of deer mice. These mice, which fed on the introduced gall flies, led to a threefold increase in hantavirus-positive rodents in the area.
Why it matters
This case serves as a cautionary example of how well-intentioned ecological interventions can trigger unforeseen and dangerous public health consequences.
A biological control project started half a century ago to destroy a stubborn invasive weed accidentally set off an ecological chain reaction that increased human exposure to a deadly virus. In 1973, wildlife officials and agricultural scientists in Montana released two species of European gall flies, Urophora affinis and Urophora quadrifasciata, to control the spread of spotted knapweed (Centaurea stoebe). Decades later, major research published in Ecology Letters and archived by the US Forest Service Treesearch database found that the flies became a common winter food source for native deer mice (Peromyscus maniculatus). The extra food helped mouse populations grow and increased the spread of Sin Nombre hantavirus.
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