From the ArcaMax Publishing, Gardening Newsletter:
http://www.arcamax.com/news/gardening/s-156711-192091
Question: I would love to have some ladybugs and other helpful insects
to aid in pollination and pest control....how do I attract them?
Should I buy some?
Answer: Beneficial insects will arrive like magic if there are insects
to eat. The best way to attract them is not to use any pesticides. You
can also purchase beneficial insects to release but unless there is a
food supply for them to eat they won't stay around very long!