I have found from experimentations as a kid that catalpa worms are usually harmful to bluegill and channel cats. That is if offered with a #4 hook in them. Other than that, they're all gonna end up in there sooner or later anyway.
Modern insecticides are low level and slow acting nerve agents to insects only; but, as CN stated, try and keep the DDT laced ones outta there. I have heard that after summer rains, large amounts of fire ants can be consumed by bluegills and kill them. You may not have that problem.
