Weed-control flies in Montana linked to tripling of hantavirus-positive mice

A biological control effort against invasive spotted knapweed in Montana has triggered an unintended ecological chain reaction. Gall flies, introduced to curb the weed's spread, have become a key winter food source for deer mice, causing their populations to surge. The rise in deer mice numbers has corresponded with an increase in hantavirus transmission in affected areas. Regions with high knapweed density are reporting significantly more hantavirus-infected mice compared to areas with native grasslands.