Did you try throwing in some lettuce or decaying vegetation into the bucket to produce infusoria? I've got a small culture growing, however, I don't have enough to supply you at the moment;( Try to avoid a place that is too windy as the chironomid cannot fight it. You can also try placing it closer to your house because light (your houselight) will attract some adults. I will admit it helps to have a neighbor's giant koi pond next door to attract swarms.
On an irrelevant side note, blood worms are the larvae of midges (aka chironomids), not mosquitos They anatomically resemble mosquitos in adult form, but they don't bite!
1. They are live and the fish think hey there's alot of good food around lets spawn.
2. They are very very very rich. So the fish can store up energy for the 5 days or so that the male is going to have to work 24/7.