Mexican Bean Beetle Invasion!

Our experience with garden pests have been very minimal...slugs and aphids.  Now that we live in the country without the suburban pesticides, we are realizing how difficult organic gardening really can be.  So far this spring/summer we have dealt with: cucumber beetles, potato flea beetles, cutworm, aphids, potato beetles, slugs, and the Mexican bean beetle.  We have spent hours and I mean literally hours, hand picking these pests.  Of course, aphids fly away and we haven't figured out the right mix of dish detergent and water for pest management control.  Any readers who have suggestions, please leave a comment!  The picture above shows a section of bean plants that have been affected by the aphids and the Mexican bean beetle.  Surprisingly the beans themselves haven't been affected, only the leaves.  

Here is a cluster of the Mexican bean beetle eggs.  One beetle can lay 40-75 eggs in a single cluster.  

Here is the larva.  These pests live on the underside of the leaves which makes finding them a bit more work.  We have 250 plants so that's a lot of leaves to turn over!

Weeks ago when we first saw this brown beetle, we thought it was a beneficial insect because the aphid population was declining.  Come to find out, it's the adult Mexican bean beetle!!  

I am so confused when it comes to knowing which bugs are pests and which bugs are beneficial.  There are so many different colors of ladybugs that I never know which ones should be left in the garden.  I left the ladybug in the above picture on the bean plants assuming it was a beneficial.  Do any of you readers have advice on identification?