Specialized pollination by carpenter bees inCalanthe striata(Orchidaceae), with a review of carpenter bee pollination in orchids

Abstract

Calanthe striata has nectarless flowers that are self-compatible, but pollinator dependent. Field observations showed that the flowers were pollinated exclusively by the carpenter bee Xylocopa appendiculata circumvolans, although the bees occasionally wasted pollen by delivering to the stigmatic surface pollinaria that retained their anther caps. Fruit set ratios at the population level varied spatiotemporally, but were generally low (8.3–17.3%). Calanthe striata blooms in spring when post-overwintering carpenter bees have not yet started foraging for brood production. It can therefore exploit an abundance of opportunistic/naive foragers. This timing may also increase the possibility of pollinator visits, because no rewarding co-flowering plants are available in the orchid habitats. A literature review of Orchidaceae pollinated by carpenter bees revealed that at least 14 species of Orchidoideae and Epidendroideae have evolved flowers specialized for carpenter bee pollination. They typically have shallow pink/magenta flowers with a foothold for pollinators; pollinaria are attached to the head, ventral thorax or base of the middle legs of carpenter bees when they insert their heads and/or proboscises into flowers; pollination success is generally low, a probable consequence of the deceptive pollination systems. © 2013 The Linnean Society of London, Botanical Journal of the Linnean Society, 2013, 171, 730–743.