While there are other pollinators in the world like birds, butterflies, the wind and other insects, they pale in comparison to the effectiveness of a honey bee colony. Most other insect pollinators are solitary creatures and of those that are social, the colony usually consists of a few hundred workers to maybe a few thousand at the end of season. Consider that a honey bee hive can begin with between 5-10,000 bees and can grow into 100,000+ while giving birth to new colonies, the sheer size of the work force makes them essential for our food supply. In addition, many social insects are one generation only meaning the previous years queen dies before winter and the young pick up the work the following spring after they overwinter. Honey bees are year round and will hibernate within the hive if it gets too cold, but can be seen active year round as weather permits. Add to this how easy they are to transport as many beekeepers who transport around their state, even around the country for pollination services will tell you. We have over 8,000 years of history interacting with the honey bee, if there is another insect that can replace it, we haven't found it yet.