Package bees are bees that are shaken out of colonies into a screened box, given a queen and a container of food sufficient for transit. They are produced early in the season in warm climates and can build up quickly, so in about 10 weeks they are ready for the nectar flow. They are packaged by weight, which varies between 2-5lb, with apparently 3lb being the most common.
Packages are a major part of beekeeping in warm or large countries, but are rarely used in cooler climates. In the U.S. the use of package bees has become part of beekeeping culture, where colony losses are often made up by buying packages, rather than by making increase from within the apiary. They are not always favoured and I think it is worth mentioning that I was asked to visit the Hudson Valley region on New York State to advise beekeepers on improving their bees. I was told that one of the problems is that beekeepers buy package bees that come from the Southern States such as California, Florida, Georgia and Texas. They are often very soft, can't survive the much colder winters, so die out quickly. The beekeeper then buys more from the same source and the same happens again, then they give up beekeeping. As with beekeeping elsewhere I'm sure the standard of beekeeping may also be a factor.
For several years after the hard 1962/63 winter in the U.K. many packages were imported from the U.S., but they weren't very successful. Many were headed by Italian or Starline queens that were very prolific. Nosema was a big problem and many colonies were soon lost. When I was increasing my colony numbers I bought 42 colonies from another beekeeper who was giving up due to failing sight. Nineteen of these were American packages he had bought the previous year. They were of the very yellow type and I lost virtually all of them with nosema the following winter, that was long and damp.
In "The World History of Beekeeping and Honey Hunting. (44.3 Package bees)" Eva Crane states that "A.I. Root (1878) was the first to experiment in transporting the adult bees of a colony without their combs and heavy hive". This made it easier to ship bees to more northerly regions, so opening up new regions to honey production. Perhaps many went to Canada where they used to kill the bees, before they developed the wintering techniques they use now. This is conjecture and I would appreciate information please.
Package bees have may uses including starting new colonies for commercial beekeepers, making up for winter losses and bolstering weak colonies. It is the most common way of starting for American hobbyists.
In the U.S. the package bee industry is huge, but for several different reasons it has had problems. The Baton Rouge Bee Laboratory lists amongst its research achievements of 1920s - 1930s "Problems in producing and shipping package bees and queens".