There are two things Ladybugs do when aphids are plentiful; eat like crazy and make love. There are lots of aphids and the population of lady bugs is building fast. Unfortunately they lag behind the aphids but once there are enough of them they can ruin a aphids day.
There are pesticide that get into the plant and kill the aphid once it sucks the sap. As organic farmers we can only use organically approved contact pesticides. Getting good contact right in the middle of chard plants like this one is difficult. The beauty of many thousands of ladybugs working for us is that they can search and consume aphids in all those hard to reach places. Over the ten years we have been on this land we have never added ladybugs. We have created a safe and abundant place for them to live. Build it and they will come has been our plan.
The fava bean crop has not gone well this year. My first plantings were over run with weeds and the later ones have black bean aphids really bad. They also have a very happy population of lady bugs. 
Our aim is not to eliminate aphids just to keep them under control.