The picture worked better for me this morning, I have no idea why it was blurry last night. That is a great photo!
The larger ones are adult aphids, the smaller ones are baby aphids. What plant(s)are they on?
Aphids can cause huge amounts of destruction both directly and indirectly. You can spray them with organic or non-organic poisons, you can squash them, you can spray warm soapy water to kill them, all of which will work well for a while but you will have to reapply these sooner or later.
Lady beetles are known for eating them, things like lacewings, some assassin bugs and a number of other insects also eat them. While they are nice to have around I have never been impressed with the results from generalist predators as they will eat something else when the prey numbers start to get lowered.
You can get parasitoid wasps in your garden by either having them turn up or buying them. They are tiny wasps that lay an egg into the aphid, the aphid then gets mummified while the baby wasp grows within it, then a wasp hatches out to look for a mate and lays eggs into more aphids. They have to kill aphids for their life cycle to continue so keep working even when aphid numbers are down. For me they kept the aphid numbers down rather well. We had them turn up in a garden a while ago and they were great and were constantly present for several years. We had a few plants that were completely covered with aphids before they turned up, within a few weeks the wasps had cleared up the entire problem for me!
The only two down sides I have noticed to parasitoid wasps is that they need aphids around to survive, in my old place behind the house where the hot water system was I left some weeds that always had aphids to keep the parasitoids going over winter. The other is that they are very specialist predators and will only lay eggs into a few varieties of aphid and not touch some other types of aphid at all. I assume if you spray with poisons of any kind they would not cope too well, but I do not spray with anything so do not have experience with this to share.
You could also try companion planting. Unfortunately most books on companion planting, even the ones written in australia, are based on northern hemisphere so are a bit hit and miss. Hopefully someone here has experience with companion planting that works for australian insects and can give some great advice on what to try.
