Controlling cabbage white butterflies naturally - Pteromalus puparum in Australia

My daughter, much like many kids her age, loves butterflies.  Butterfly kits where they send you a chrysalis to hatch are very expensive.  Native butterflies have a hard enough time as it is so I would prefer my daughter just watch them in the garden and we didn't collect their chrysalis.

My vegetable garden, much like many organic vegetable gardens, has cabbage white butterflies.  There are canola fields less than one kilometer from my house, spilled canola seed on roadsides acts as a breeding ground for these pests, and they flutter over my fence all summer long.  I often collect pupa or caterpillars from plants and feed them to the chickens. 

I have heaps of caterpillars, and my daughter wants butterflies.  Can you guess where this is going…

I collected some cabbage white pupa and put them in a jar for my daughter.  She got to watch a few butterflies emerge.  We also caught a few adult cabbage white butterflies and put them in a little enclosure to watch them flutter around.  It was heaps of fun.

Later in the season when I collect cabbage white caterpillars off my plants I plan to give them to my daughter to grow into butterflies.  She should enjoy that.  Cabbage white butterflies are an introduced pests, so catching these is not a problem.

Everything went well and my daughter was proud of her butterfly farm.  Then something strange happened to one of the pupa.  It turned the wrong shade of brown, a small round hole appeared in its side, and a bunch of tiny pteromalid wasps emerged.  My daughter was horrified and thought they were ants.  The truth was far more horrifying when I explained it to her, they were little parasitoid wasps and had eaten the pupa from the inside. 

Pteromalus puparum photo from - https://www.inaturalist.org/taxa/264352-Pteromalus-puparum

These parasitoid wasps presumably mated and laid eggs in the other pupa that were in the jar.  Eventually I had a jar full of tiny parasitoid wasps and dead hollowed out butterfly pupa.  We gladly released these wasps into my vegetable garden.

These wasps appear to be Pteromalus puparum.  They are a pupal endoparasite of several butterflies, they search out pupa and inject venom and eggs into the host.  The number of eggs they lay in a host varies depending on the size of the host.  Once the eggs hatch they eat out the host from the inside, then they pupate and emerge as adults who mate and look for more hosts in which to lay eggs.  They have been used overseas to help control numbers of cabbage white butterflies.

I am unsure when these wasps were introduced into Australia, but I am assuming it was not terribly long ago.  These tiny wasps were once sighted in VIC, WA, and northern QLD.  Many references state it was introduced in Australia but its establishment is uncertain.

Following some incredibly bad advice from Jerry Coleby Williams and Gardening Australia I planted land cress (Barbarea vulgaris) to help control cabbage white butterflies.  It didn't work.  These parasitoid wasps, however, have been proven to reduce the numbers of these butterflies and have been introduced here and several countries in an attempt to combat these pests.

This is incredibly exciting, if these parasitoid wasps can establish a background population in my area they may help to control cabbage white butterflies.  Don’t be fooled, they won’t ever eliminate these pests for me, but they should help to lower their numbers.  Lower numbers of pests means less damage to crops.

I grow everything organically.  If I spray insecticides, even organic insecticides, then these tiny wasps will be the first to die.