Andrea, there are several tricks to induce them to stay put at least long enough to eat your infestation.
1. Put the box of them in the refrigerator for an hour or two before release so that they are metabolically too sluggish to fly off.
2. They will be thirsty from their time spent in shipment. So go outside and spray down the plants upon which you want to put them. They'll be more likely to stay put if they don't have to immediately fly off in search of water.
3. Sprinkle them after dark. They are less likely to fly after dark.
It really does work if you use these tricks. The growing points on my mums, roses, and spireas were simply coated with aphids. By morning the ladybugs were gone, but so were all the aphids. And presumeably they had left plenty of eggs behind, because I haven't had a problem with aphids in any of the years since then.
I have also discovered that white mums attract hoverflies, which also eat aphids.
One year I had an infestation of stinkbugs on my tomato plants. I read that there is a type of small wasp that preys on them. So that fall, I made sure all the tomato leaves got thoroughly bagged up, and told our pest control service to stop knocking down wasp nests and spider webs. The next year I saw little wasps hovering around my new tomato plants, and I have never again had a problem with stink bugs on them since.
Predatory insects do work to keep things in balance if you don't go killing them off.
