A deeply interesting subject...

As you'll have seen from most of the answers so far, it's now generally frowned upon to introduce insects and other species to environments where they haven't already evolved or invaded by themselves.

But planting *can* work, if the environment is right and you've got enough resources and / or patience. And under some circumstances - for instance, localised extinction of a pre-existing species, it can be justifiable to reintroduce that species *if* the conditions that caused the extinction in the first place have been successfully addressed.

Here's an example of what I mean - *all* of it, from the UK ...
[url=http://www.vegsoc.org.au/forum_messages.asp?Thread_ID=510&Topic_ID=10:ceb41]http://www.vegsoc.org.au/forum_messages.asp?Thread_ID=510&Topic_ID=10[/url:ceb41]

Sadly, the last I heard was that Dr Bennett has given up the experiment, preferring emigration to somewhere less environmentally unfriendly. But without those toxins in the water, it's believed that he could achieved enough of a critical mass to get those mayfly going again...

Theo