It's interesting, but two weeks ago my garden was infested with aphids. Green and black they were everywhere.
Now they are all gone. Can't have been ladybird or lacewing. Not for that volume.
Had a bit of a Google, and apparently house sparrows need aphids for their young in the first few days. The eradication of bugs by chemicals is causing the sparrow numbers to drop, as seed feeders don't help in the baby sparrows first days.
So by trying to get rid of the problem, people are making it worse.
My garden is pretty much in balance. I do weed and feed the lawn in parts. Although I think I will just feed it from now on. I add chook poo, blood and bone and ash as fertilizer. I don't use pesticides. I do occasionally use path weed killer out the front. But some weeds don't go by weeding.
Apart from that, it pretty much it takes care of itself.