The Botanical Garden of the University Salzburg is not only a habitat for many different plant species but also a showcase for research. In spring 2017, a very interesting Bachelor Thesis took place in the berry garden. Nina Haas from the study group of Univ.-Prof. Dr. Stefan Dötterl, Department of Biosciences, studied the reproductive biology of the black currants (Ribes nigrum L.) and gooseberries (Ribes uva-crispa L.). She observed the flower visitors and examined the impact of these insects on the fruit set of the plants. Moreover she discovered the scents’ compounds of the flowers and found out which of these compounds are detected by the visitors.
The following questions were addressed:

do flower visitors have an impact on the fruit set of gooseberries or black currants?

The results of this fascinating project showed that gooseberries are insect-pollinated. They can also self-pollinate, however very insufficiently. The black currants are efficient self-pollinators, albeit the flower visitors improve the fruit set significantly. To measure the effect of the flower visitors on the fruit set, an exclusion experiment was performed. For this experiment some branches of each individual plant were wrapped into a sheer curtain to avoid insects getting in contact with the flowers before the buds bursted open. At the time the fertilized ovaries started to thicken, the fruit set was calculated from both, the open and the wrapped branches.
black currant plant with wrapped branches

which insect species visits gooseberry and black currant flowers?

The famous honeybee (Apis mellifera) was definitely the most frequent visitor of both plant species. In second place are the tawny mining bee (Andrena fulva) and the large earth bumblebee (Bombus terrestris). Also other bee- and bumblebee species were observed. Interestingly, wasps also visited the flowers of both plant species and syrphid flies visited only black currants. Moreover it was observed, that many ants frequented the gooseberry flowers. It’s already assumed that they can act as pollinators (Rostás und Tautz 2010), but further studies are required to resolve this debate.
To determine the frequency of the flower visitors, the plants of interest were observed for several days in certain time frames. The insects visiting the flowers within this timeframe were recorded and the relative visiting frequency calculated.
Honeybee (Apis mellifera) visiting a gooseberry flower
honeybee visiting a gooseberry flower

Large earth bumblebee (Bombus terrestris) visiting a black currant flower
large earth bumblebee visiting a black currant flower

Tree bumblebee (Bombus hypnorum) visiting a black currant flower
tree bumblebee visiting a black currant flower

Red-tailed bumblebee (Bombus lapidarius) visinig a black currant flower
red-tailed bumblebee visinting a black currant flower

Ant (Formidae sp.) visiting a gooseberry flower
ant visiting a gooseberry flower

what are the compounds of floral scent in goosebeeries and black currant and which if them can be detected by visiting inscets?

 The scent detection discovered around 20 compounds in the gooseberry scent. The main compounds are Methyleugenol, Linalool oxide furanoid, Methylbutanol, Heptane and an unknown substance.
The black currant scent contains around 40 compounds and many of them are very strong. The main compounds are Arbusculone, Linalool oxide furanoid, Linalool, Lilac aldehyde, Linalool oxide pyranoid, Lilac alcohol, Linalyl acetate, Geranyl acetate and some unknown substances. Most of the components could be detected by the tested visitors. There were only a few differences between the honeybee and different bumblebee species. For the discovery of the scent compounds, the scent was collected using a very specific method. For each sample a twig was bagged with a plastic oven bag to accumulate the volatiles. Following that, the air within the oven bags was drawn through a filter by a small pump. Next, the obtained volatiles in the filter were analysed using gas chromatography.    

collecting scent from a black currant plant

To find out whichh of these compounds can be detected by the insects, electrophysiological measurements were performed.
For this analysis an insects antennae was arranged between two electrodes. Then the scent compounds were blown onto the antennae and the electric signals of the antennae were measured. 
Barrierefreiheit: Kurzbeschreibung des Bildes
 The components of the black currant scent are visible as peaks of the black graph. The electric signals of the insect antennae to the individual components are visible in the two blue graphs below.  

With all these interesting findings we made progress in understanding the arthropod-plant interactions and the reproductive biology of the gooseberries and black currants. The Botanical Garden of the University of Salzburg is proud to enable fascinating research projects along with many other exciting investigations.