Ya, I'm waiting for the weevils to say, "fuck this Salvinia shit, this (insert cash crop here) is AWESOME!"

Nutria don't die off every winter, so the weevils are likely to be less of a problem. There was actually a small scale trial before they built the weevil greenhouses, which didn't uncover any major issues with them.

See https://features.texasmonthly.com/editorial/creature-green-lagoon/ for many more details including the lack of frost tolerance:

Still, their campaign faced a significant obstacle: Caddo’s unfortunate latitude. The bug, like the plant it craves, is tropical. Problem is, weevils are felled by frost, while salvinia can stand slightly lower temperatures. This has proven to be Caddo’s curse, said Julie Nachtrieb, a biologist who raises and studies salvinia weevils at the Lewisville Aquatic Ecosystem Research Facility, part of the U.S. Army Corps of Engineers. In places with mild or even nonexistent winters, weevils can be released a few times and then “you can walk away and let nature take its course,” she said. But at Caddo, the weevil populations must be reconstituted every spring, giving salvinia a running start.