Buying bugs

For the most part I try my best to let nature keep the bad bugs in check.  I have BT and cold press neam oil, but haven't opened them. Even though they are "organic" I don't like that they, or at least the neam oil kills indiscriminately.  
I have gotten away with spraying off the aphids with water,  that seems to get out of control on my beans in late August.  
I work for a Co-op, and they sell ladybugs, praying mantis eggs, and one other I can't think of at the moment. I have been tempted to buy both from time to time. I haven't so far. You might think I'm strange, but I always think about how people have transplanted things (insert fish, animals, plants, etc.).  And it changed the dynamic of the hole ecosystem.  I wonder are all species of ladybug, or praying mantis the same?  If I buy them will I add genetic diversity and strengthen the gene pool, or will I buy bully bugs that kill the bugs I have.
I know all the problems in the world, and I'm worried about ladybugs. Call me strange, it's ok, I know.
I was thinking about it today (probably because something is eating my potato leaves, and I have been seeing lots of ladybug.  So I thought I would post, and see if any of you amazing Permies people have any answers or thoughts on the matter.
Thanks

Hi Jen,
I just listened to a good podcast the other day on organic pest control. The expert was talking about how ladybugs and praying mantis are both good, but do not always do what people expect. They can eat good bugs too, and will often scatter and not stay in your garden or even yard, like people think. So you get less impact than you expect when buying those.

I don't think you will have to worry about them being transplanted... chances are you already have ladybugs and praying mantis around, just not enough.

Another thing that comes to mind is that bugs tend to target the weakest or sickly-est or most stressed plants. The fact that they are becoming a problem in August, tells me there a chance that your beans are getting stressed in August. I'm not familiar with N. California weather, but I would guess it might be hot that time of year :) Is there something you could do to reduce their stress? Perhaps try a more heat-tolerant variety?