The possible ecological implications of the invasion of Bombus terrestris (L.) (Apidae) at Mt. Carmel, Israel.

Bombus terrestris invaded Mt Carmel about 2 decades ago and since then has shown a constant expansion. Observations on bee visits to Arbutus andrachne (1980-1994) and Capparis spinosa (1982 and 1994) showed a progressive increase in B. terrestris, associated with a reduction in honey bees and various species of solitary bees. B. terrestris is active mainly from dawn until 09.00 h, at temperatures as low as 15°C and at a relative humidity of up to 95%. Due to the bee's early and very efficient foraging, nectariferous plants are almost empty of nectar by about 09.00 h, causing a clear reduction in the activity of other bees at these plants. Analysis of pollen grains on the bodies of bees and direct observations revealed that the activity of B. terrestris in midsummer, when nectariferous plants are rare, seems to depend on nectar from garden plants. Due to its long flight range, B. terrestris is also able to forage in burnt areas which few other bees are able to exploit because of the scarcity of rewarding plants and their short flight range. It is concluded that the invasion of B. terrestris on Mt Carmel is a threat to the biodiversity of the local bee fauna, including the honey bee. Its practice of nectar robbing may also affect seed production in the plants it exploits.