It's a systemic insecticide which is applied to the compost/root area and which is absorbed into the plant. It kills the weevils when they subsequently eat the plant by endocrine disruption.
If it has only just happened and there has been no time for the plants to absorb the pesticide, I'd suggest taking the plants out of the compost and washing the whole plants - leaves and roots then re-potting in fresh compost. If it's been a while since they were drenched and they've had time to take up the stuff, I'd bin them.