Released about a hundred lady bugs into the greenhouse about a month ago, to help control the aphids.

I was hoping some would stay in the greenhouse, mate and lay eggs.

Look! These are lady bug larvae! They kinda look like tiny alligators. You definitely want to know how to identify these little guys and keep the around. The lavae are hungry and devour dozens of aphids a day. They also chomp on mites and insect eggs.

I already don't use any pesticides and in aquaponics using organic or natural products like insecticidal soap is dangerous for your fish and bacteria colonies. Most aquaponics setups are also placed in greenhouses which come with a particular set of pests and diseases. The best control once these pests are present are beneficial insects. It's best to try and keep these pests out in the first place, always thoroughly inspect the plants you bring in and it's best whenever possible to start your own from seeds or cloning.