The importance of scent and nectar filters in a specialized wasp‐pollination system

Abstract

Summary 1.Plants with open flowers and exposed nectar should attract a wide diversity of flower visitors, yet, for reasons that are not yet well understood, some plants with these 'generalist' floral traits have highly specialized pollination systems. 2. We investigated this problem in the African milkweed Pachycarpus grandiflorus which has open flowers that produce copious amounts of exposed and concentrated nectar, yet is visited almost exclusively by spider-hunting wasps in the genus Hemipepsis . 3. These wasps were the only visitors found to consistently carry pollinaria and a cage experiment showed that they are capable of successfully pollinating this plant. Furthermore, experimental hand-pollinations showed that P. grandiflorus is genetically self-incompatible and thus reliant on pollinators for seed set. 4. We investigated the roles of chemical (nectar and floral scent) and spectral properties in the selective attraction of wasps and the filtering out of other potential flower visitors. Nectar palatability experiments showed that the nectar is unpalatable to honeybees but palatable to the wasps. Choice experiments conducted in the field and using a Y-maze in the laboratory showed that wasps are attracted primarily by scent rather than visual cues. Analysis of scent using Gas Chromatography-Mass Spectrometry showed that these inflorescences produce 36 different compounds, mostly monoterpenes and aliphatics. Analysis of spectral reflectance showed that flowers have similar colouring to the background vegetation. 5. We conclude that P. grandiflorus is specialized for pollination by Hemipepsis wasps, and in the absence of morphological filters, achieves specialization through unpalatable nectar, cryptic colouring and scent as a selective pollinator attractant. 6. This study demonstrates that plants whose flowers are not morphologically adapted to exclude particular floral visitors can achieve specialization through non-morphological filters.

Fly pollination of dichogamous Angelica sylvestris (Apiaceae): how (functionally) specialized can a (morphologically) generalized plant be?

“…of pollen grains), U mean no. of umbellets visited within an umbel (calculated based on video-recorded visits), M male (staminate) phase umbels, F female (pistillate) phase umbels pompilid wasps (Shuttleworth and Johnson 2009). As demonstrated by these authors, olfactory cues were found to be primary attractants in the system; also the plant produced nectar that was unpalatable to honeybees.…”

Flower-Visiting Social Wasps and Plants Interaction: Network Pattern and Environmental Complexity

“…Although wasps are more frequently regarded as floral resource thieves [3][4][5][6], recent papers show that wasps can also effectively contribute to pollination [7]. In a study with Schinus terebinthifolius Raddi (Anacardiaceae), Sühs et al [8] showed that social wasps, especially Polistes versicolor (Olivier, 1791), Polybia sericea (Olivier, 1791), Polistes simillimus (Zikán, 1951), and Polybia ignobilis (Haliday, 1836), were more representative in richness and abundance than bee species, being considered efficient pollinators.…”

Social wasp richness and species distributions among ecosystem types in Minas Gerais, Brazil

“…Although wasps are more frequently regarded as floral resource thieves (Hunt et al, 1991;Santos et al, 2010); recent papers show that wasps can also effectively contribute to pollination (Shuttleworth & Johnson, 2009). In a study with Schinus terebinthifolius Raddi (Anacardiaceae), Suhs et al (2009) showed that social wasps, especially Polistes versicolor (Olivier, 1791), Polybia sericea (Olivier, 1791), Polistes simillimus (Zikán, 1951), and Polybia ignobilis (Haliday, 1836), were more representative in richness and abundance than bee species, being considered efficient pollinators.…”