Introduction of Bombus terrestris onto mainland Australia: Possible consequences for native biota

Australia has a recent history of introducing animal and plant species that were thought to be useful and harmless, but which sadly turned out to become a pest or cause extinction of native species. The purport of this presentation is: Let's learn from the past and do proper research before introducing yet another new species into Australia, thereby preventing any potential new disasters.

I have asked many people working in different areas what threats could potentially be posed by introduced Bombus terrestris in the Australian mainland. These people are:

Dr Rod Randall	Agriculture WA	Weeds in WA
Dr David McKenzie	DNRE Victoria	Weeds in Victoria
Dr Carolyn Gross	University of New England	Pollination of native Australian plants
Dr Manja M. Kwak	Groningen University	Bumblebees as pollinators
Dr David Paton	Adelaide University	Honeybees as competitors of native birds
Andrew Hingston	University of Tasmania	Bumblebees as competitors of native bees

The 10 minutes set aside for this presentation, does not suffice to address threats in full. Therefore, potential problems are pointed out using examples, and indications are provided that these problems are not imaginary.

1. Competition with native bee species: Lowered reproductive success of native bees can be expected through:

   (A) Increased nectar or pollen competition due to the fact that (1) bumble bees visit native plants that are not used as a food source by honeybees (Hingston 1998); (2) Bumblebees start foraging at temperatures as low as 13^oC, and could deplete flowers of resources before native bees start foraging.

   (B) Active displacement which has been shown to occur for two Chalicodoma species (Hingston and McQuillan 1999).

2. Competition with native birds: Lowered reproductive success of nectarivorous birds can be caused by:

   (A) Displacement of native birds on flowers. Paton (1997) shows that increased density of honeybees affect foraging patterns of New Holland honeyeaters. At low bee density, the honeyeaters forage the whole day, while at high density they foraged during early morning & late afternoon. Early morning foraging by B. terrestris could affect birds that already suffer from displacement by honeybees later in the day.

   (B) Nectar robbery from bird pollinated plants. Bumblebees take nectar from flowers with a long corolla by making a hole at the base of the corolla (e.g. bearded heath, Epacris impressa). Such flowers are specialised for bird pollination. Honeybees, who do not make the holes themselves, also obtain nectar through these holes. This means that competition could increase for native honeyeaters.

3. Reduced seed production by native plants: Active or passive displacement of native pollinators can lead to reduced seed production. Competition with native bees for pollen can lead to reduction in native plant pollination for plants that are visited for their nectar or the other way around.
4. Increased seed production and proliferation of weed species: Several sleeper weeds may become problematic once the appropriate pollinator is introduced. Bumblebees are buzz pollinators, and are likely to spread over areas were large buzz pollinating bees presently occur at very low densities (VIC, and cooler parts of NSW and SA). Among plants that could become serious problems are: foxgloves, snapdragon, Polygala, and several solanaceous species. Some of these species are weeds in New Zealand, where Bombus species were introduced about a century ago. In addition to proliferation of sleeper weeds, seed production of some already problematic weeds such as blackberry may increase, leading to aggravation of the problem.

While opportunities for investigating some of the effects are available because of the recent introduction and spread of Bombus terrestris in Tasmania, other effects cannot be investigated due to differences between Tasmanian and native biota. Priority should placed on investigating potential effects for proliferation of weed species, while effects on foraging behaviour of one or more of six Tasmanian honeyeater species should be analysed experimentally. In addition, the potential for native alternatives to Bombus deserves attention.