Diversity and origins of Fijian leaf-cutter bees (Megachilidae)

Bees are key pollinators in almost all terrestrial ecosystems and can have major roles in agricultural production. Records of bees in the Southwest Pacific indicate a very low diversity, with the Fijian bee fauna one of the least diverse, despite an otherwise rich biota. Megachilid bees represent a large proportion of the bee fauna for almost all island groups in the Southwest Pacific and, because they are wood- and stem-nesting, their wide distribution is likely to have been influenced by rafting and anthropogenic maritime trade. Our study is the first to apply molecular techniques to the study of megachilid bees in this region and indicates between four and five recent introductions to Fiji, likely from Southeast Asia. The study also provides the first record of Heriades (Michenerella) in the Southwest Pacific and the first record of the subgenus Megachile (Callomegachile) in Fiji. These results indicate that a large proportion of the Fijian bee fauna is likely to have been introduced only very recently and, therefore, has had only a very recent role in Fijian ecosystems, despite their current abundance. This has very wide implications for understanding Fijian plant-pollinator relationships. We argue that there is a strong need to understand ancient plant-pollinator relationships that may have evolved in Fiji before the mid-late Pleistocene and Holocene and whether these could be disrupted by recent bee introductions.