Notes on Bumblebees in Tasmania

Roger Buttermore
Tasmanian Museum & Art Gallery
April 1997

For images of Bumblebees

Bombus terrestris is one of a few hundred world-wide species of bumblebees, which are mostly native to the Northern Hemisphere. Certain species have been recognized as valuable pollinators of red clover since Darwin's time. Around 1885 and continuing up to the turn of the century, bumblebees were successfully introduced to New Zealand from England but similar efforts failed in Australia when bees from Christchurch were brought over. Until to the last ten years, B. terrestris has never been a particularly desirable species because it is not a good pollinator of red clover.

The species was accidentally introduced to New Zealand in 1885 and is the most successful one there, quickly occupying every island. Tasmanian specimens are thought to have arrived via New Zealand despite a rigorous quarantine. They have since distributed themselves north to Longford and south to Southport. B. terrestris is expected to spread throughout Tasmania and probably mainland Australia by either human intervention or island hopping.

There is some concern over competition with other animals for food resources as bumble bees penetrate the Australian bush but their ecological impact in New Zealand is generally perceived to be minimal. Populations are most numerous in suburban areas, where nectar and pollen are available almost year-round.

In nature, in the early spring, bumblebee queens emerge from the ground (where they dug themselves in the previous summer) and begin a nest. They have to feed themselves, find a nest site (usually in the ground), and provision it without assistance before laying their eggs, which have to be incubated. It then takes about a month for the first workers to grow to adult size from eggs, and begin to help the queen.

As spring progresses into summer, the colony grows with more workers which are all female. Over a thousand cocoons have been found in some nests, though most colonies are much smaller than this. Workers die about six weeks after attaining their adult form. Queens and workers are capable of stinging several times because the sting is not barbed as in honey bee workers.

Drones are produced when workers bring in a surplus of nectar and pollen. The males leave the nest very soon, feeding themselves while searching for nubile queens, who mate only once. Mating takes place outside the nest. Drones have a very short life, but can mate several times.

After 3-4 months, depending on food resources, new queens begin to emerge from their cocoons. As the new queens prepare to leave the nest permanently, workers and the old queen become listless and die.

In their native environment the new queens go into hibernation (more correctly termed diapause), but in Tasmania and New Zealand, due to milder weather, it is not unusual for new queens to start a new colony immediately after leaving their mother's nest, thus producing at least two generations of queens per year.

Bumblebees have advantages over honeybees for crop pollination, especially when used in greenhouses but it was not possible to raise them year-round until the late 1980's, when a French researcher discovered how to artificially break B. terrestris queens' winter diapause cycle. The species has recently acquired considerable commercial importance as a pollinator of tomatoes grown in glasshouses.

In New Zealand, Europe and North America, thriving, laboratory cultured Bombus colonies of 30-100 bees are now sold for a couple of hundred dollars each to glasshouse horticulturists. Each hive will probably last 5 months at most, because they are annual, not perennial like honeybee hives. The industry generates about $A50 million per annum world-wide to pollinate crops worth an estimated $A5 billion.

Recent research indicates that the Tasmanian bumblebee population is inbred but obviously not critically so. We suspect that the entire population of B. terrestris in Tasmania is descended from a single fertilised queen. This is a unique situation which is of great interest to bee geneticists and evolutionary biologists.