Any pesticide on the plants will be dripped into the water and will kill your fish. Therefore , dealing with insects is tricky.
About the only thing you can do is to plant 'stinky' things that repel insects. My favorites are :
bunching onions, basil, and french marigolds. I scatter the 'stinky plants' throughout the system with extras near the beans , peas and cabbage type plants. The onions and basil we eat when they mature,
the marigolds are just pretty. French Marigolds will grow into huge creatures
and take over your system , if you let them. They need heavy pruning and after a couple of months replaced with new small starts. I take the old marigolds and plant them in the ground nearby . They rarely even wilt and continue to grow and chase away the insects.
We have small mosquito fish living under the vegetable troughs to control the
mosquito population. The mosquitoes lay eggs in the water and the tiny mosquito fish
eat the larvae . Occasionally the mosquito fish population explodes and we scoop out a
few and the chickens have a treat eating the extra small fish. .