I always use Nippon, but carefully. Try to find where their "main entrance"
is and place one drop on a piece of plactic (say) so that an ant comes
across it and gallops back to call his friends! When they are crowding
round like cattle at a pond, add a few more drops nearby. Keep them well fed
like that and you'll soon be rid of them.

Your nibbled carrots sounds like carrot root fly problems. Peg (a twig
slightly split with a knife) up a few pieces of fly catcher (the yellow ones
for greenhouses) just clear of the ground near the carrots and see what is
caught. Carrot root fly are supposed to be stopped by low barriers so how
are they getting on to a raised bed: have you installed stairs?!!!

Regards

Geoff