Mae Carson, of Otaki, asks :-

What is the life cycle of the bumble bee and does it pollinate plants?

David Pattemore, a pollination biologist with Plant & Food Research with a special interest in bumble bees, responded.

Bumble bees are colonial bees. A queen and her daughters live in a colony, gathering nectar and pollen from flowers and raising young bees in wax cells, similar to honey bees. Like all bees, bumble bees have evolved a special relationship with plants, where they take sugary nectar and nutritious pollen from flowers and in doing so pollinate the flower which then produces seeds.

Unlike a honey bee colony, each bumble bee colony dies off at the end of each summer. The only bumble bees that survive are the newly hatched queen bumble bees who mate and then look for a hiding spot in the ground where they will hibernate over winter.

Each spring, the queens emerge from hibernation and forage for themselves. They soon start looking for a new hole in the ground to start a nest. At this stage, you can often see these queens (which are much larger than worker bumble bees), zig-zagging low over the ground and even coming into buildings as they look for nest sites. Once they find a good site, they start building a colony from scratch: laying eggs, building wax cells and collecting nectar and pollen.

The eggs hatch into worker bees, who are all females. These workers start looking after the nest and foraging to support the colony. As the colony grows, the queen stops doing much apart from laying eggs, and the workers take over all the pollen- and nectar-collecting work. These colonies can grow until they have many hundreds of workers. While this is large, it is no way near as large as honey bee colonies, which have tens of thousands of workers.

But a strong bumble bee colony can make a big contribution to pollination, despite its smaller numbers. Part of the reason is the larger size of bumble bees, who need to visit more flowers each trip. Thus a bumble bee pollinates more flowers than an individual honey bee.

Another important reason bumble bees make great pollinators is they store only a few days of honey supplies. In bad weather they still need to go out and forage, whereas a honey bee stays in the warm hive living off its larger reserves.

As the colony gets large in summer, changes start to occur. The queen gets older and weaker. The colony starts producing males and the next generation of queens. Both leave the nest to mate with other bees from other colonies. The colony dies, leaving just the new queens who look for somewhere to hibernate and begin the cycle again.

Both honey bees and bumble bees were introduced by humans in New Zealand. They are not native. We do have native bee species, but none that form colonies like honey bees and bumble bees.

Four bumble bee species were introduced to New Zealand. The most common species, the buff-tailed bumble bee (Bombus terrestris), is found throughout the North and South Islands, and colonies of this species can be bought to place in your garden. The other three species are less common, with one restricted to just a few locations in the South Island.

For more information on this topic you could see the June 2015 issue of New Zealand Geographic or google my name to find the TEDx talk I gave in July 2015 in Tauranga.

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