US released weevil to fight musk thistle; it later attacked 25 native thistles
A biological control program in the US introduced the thistle seedhead weevil to manage invasive musk thistles. The initiative backfired when the weevil began attacking native and endangered thistle species, illustrating the risks of biological intervention in complex ecosystems.
Why it matters
It serves as a critical case study on the unintended ecological consequences of using non-native species for pest control.
A biological control programme launched in the United States more than five decades ago has become a cautionary example of how attempts to manage invasive species can produce unexpected ecological consequences. According to a USDA Forest Service assessment of invasive species in the Southwest, the thistle seedhead weevil (Rhinocyllus conicus) was introduced to the US between 1969 and 1972 to help control musk thistle and other invasive thistles. The insect was expected to weaken the plants by attacking their reproductive structures and reducing seed production. However, after becoming established and spreading beyond its original release areas, the weevil also began feeding on native thistles. Its impact eventually extended to numerous native species, including endangered native thistles.
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