The Chemical Basis of Host-Plant Recognition in a Specialized Bee Pollinator

Abstract

Many pollinators specialize on a few plants as food sources and rely on flower scents to recognize their hosts. However, the specific compounds mediating this recognition are mostly unknown. We investigated the chemical basis of host location/recognition in the Campanula-specialist bee Chelostoma rapunculi using chemical, electrophysiological, and behavioral approaches. Our findings show that Ca. trachelium flowers emit a weak scent consisting of both widespread and rare (i.e., spiroacetals) volatiles. In electroantennographic analyses, the antennae of bees responded to aliphatics, terpenes, aromatics, and spiroacetals; however, the bioassays revealed a more complex response picture. Spiroacetals attracted host-naive bees, whereas spiroacetals together with aliphatics and terpenes were used for host finding by host-experienced bees. On the intrafloral level, different flower parts of Ca. trachelium showed differences in the absolute and relative amounts of scent, including spiroacetals. Scent from pollen-presenting flower parts elicited more feeding responses in host-naive bees as compared to a scentless control, whereas host-experienced bees responded more to the nectar-presenting parts. Our study demonstrates the occurrence of learning (i.e., change in the bee's innate chemical search-image) after bees gain foraging experience on host flowers. We conclude that highly specific floral volatiles play a key role in host-flower recognition by this pollen-specialist bee, and discuss our findings into the broader context of host-recognition in oligolectic bees.

Deceptive Ceropegia dolichophylla fools its kleptoparasitic fly pollinators with exceptional floral scent

“…Generally, spiroacetals are rare constituents of floral scent. Just recently spiroacetals were shown to have a function in attracting pollinators, as they are key signals for host plant recognition of a solitary bee that specializes on Campanula flowers (Milet-Pinheiro et al, 2013). …”

Improving our chemistry: challenges and opportunities in the interdisciplinary study of floral volatiles

“…A fundamental requirement for laboratory analyses and manipulative eld studies alike is access to high purity, authentic VOCs with the appropriate isomeric or enantiomeric conguration. These criteria are crucial not only to the study of specialized pollination systems driven by novel compounds, 96,97 but also to the study of ubiquitous VOCs like limonene (which is chiral) and b-ocimene (which has geometric isomers). It can be difficult or prohibitively expensive for biologists to acquire sufficient amounts and purities of such compounds from commercial sources.…”

Volatiles from <i>Prunus persica</i> Flowers and Their Correlation with Flower-Visiting Insect Community in Wanbailin Ecological Garden, China

“…In some specialized pollination context, only one or a few specific floral volatiles mediate communication with specific pollinator species, and pollinators are attracted by a blend of widespread volatiles [24]. Specialized relationship between specialized pollinator and host-plant flowers is commonly mediated by specific volatiles [25].…”

“…The volatile composition of floral scents is not static, spatiotemporal variability in the identity and complexity of scent bouquets could provide critical information for the mediation of 118 Advances in Entomology volatiles to make foraging choices [27] [28]. Floral scents have the advantage in that they can supply pollinators a species-specific identity to flowers with their potentially infinite composition and diversity [25] [27]. That Prunus persica fruits need flower-visiting insects, and floral scents play a key role in pollinating.…”