Small little caterpillars are eating bougainvillea leaves as fast as they can sprout. Years ago nothing bothered a bougainvillea. Now it seems to be a constant battle. There are a couple of options you can do to help control them. Spray with organic Thuricide which only kills worms and caterpillars. You will need to reapply every week or two to keep them looking pretty and to stop the cycle.  Another alternative is to drench the soil with Bayer Tree and Shrub Protect and Feed. This works systemically to prevent and to kill insects for up to 9 months. It is also labeled for containers.

–DeAnna