The Natural Enemies Handbook has endured as the most comprehensive guide to biological control agents ever made available to practitioners. This practical guide helps you identify and understand the biology of predators, parasites, pathogens, competitors, and antagonists that help control specific insect, pathogen, nematode, or weed pests.
If you want to find out what that bug is that seems to be eating your roses, this is a good book, it goes over good bugs and bad bugs, and has graphic images of exactly how the good bugs kills the bad bugs (many times by eating them from the inside out). If you're stomach is weak, you may want to go with a book that just had I.D. photos of bugs.
My only complaint, is that I would have liked to have seen more actual I.D. photos, instead of illustrations(so I wouldn't have to buy an other book).
A big help if you are trying not to use pesticides in your garden.