Potential Displacement of the native bumblebee Bombus dahlbomii by the invasive Bombus ruderatus in NW Patagonia, Argentina

MORALES CAROLINA LAURA, AIZEN MARCELO ADRIÁN

Riberao Preto, Brasil

Conferencia; 8th IBRA International Conference on Tropical Bees and VI Encontro sobre Abelhas; 2004

International Bee Research Association (IBRA)

Abstract Introduction of pollinator species with high invasive potential may affect native pollinator species due to competition for floral resources. The European bumblebee Bombus ruderatus was introduced in Chile in 1982 for enhancing Trifolium yields. Eleven years later, it was recorded in NW Patagonia, Argentina, where today is one of the most abundant and generalist flower-visiting species. In a long term study, we observed increasing visitation frequency of this species to the flowers of herbaceous Alstroemeria aurea, compensating a simultaneous decrease in visitation frequency by the native Bombus dahlbomii.  Whereas no individuals of Bombus ruderatus were observed visiting A. aurea in 1995, the number of individuals of B. ruderatus per flower almost doubled the number of B. dahlbomii in 2001, and it was almost 45-fold higher in 2003.  The cause-effect relationship between both phenomena has not been established, yet the possibility that B. ruderatus is outcompeting and eventually displacing B.dahlbomii should be seriously considered.  Bombus dahlbomii is the most efficient pollinator of A. aurea, thus a potential displacement by its exotic congener could threat the pollination of this key plant species.  More generally, both bumblebee species visit a similar plant species assemblage, but the efficiency in pollen transfer may differ between them because differences in body size.  We propose that the introduction of exotic species should be preceded by a careful assessment of their potential impact on native biota.