Orbea lutea subsp. lutea

Zakres badania

The study by Shuttleworth, Johnson and Jürgens concerns the nominate subspecies of Orbea lutea, also accepted in POWO. Field observations in South Africa covered insects visiting flowers, their behaviour, head and floral-structure dimensions, scent profiles and pollination success. [Shuttleworth et al. 2017] [2-WWW]

Mechanical selection of visitors

Flies from several families arrived at the flowers, but repeated probing of the centre and the presence of pollinaria were found in females of one Atherigona species. They first licked tiny liquid droplets from the outer corona lobes, then followed their ridges towards the centre. Inner lobes directed the insect's head towards the guides between anthers. [Shuttleworth et al. 2017]

Morphometrics showed that the small head of Atherigona fitted the corona passages. Larger flies could land on the flower but had restricted access to the site permitting pollinium removal and deposition. This is an example of specialization achieved at the stage of contact with reproductive organs despite attraction of a broader insect group. [Shuttleworth et al. 2017]

Scent and antennal response

Volatile sulphur compounds dominated the scent, including dimethyl disulphide and dimethyl trisulphide, with considerable variation in the proportions of other components. An electroantennographic study of a single female Atherigona produced a clear antennal response to dimethyl trisulphide. This measurement documents detection of the substance by the receptor, supplementing behavioural observations in the wild. [Shuttleworth et al. 2017]

Nectar and pollen transport

Very small liquid droplets interpreted as nectar were observed on the flowers. As insects took up the liquid, they moved their mouthparts within structures responsible for pollen transport. The authors measured pollinarium removal, pollinium deposition and fruit set separately. Comparing these stages allows the process's efficiency to be described. [Shuttleworth et al. 2017]