Training experiments with Bombus terrestris and Apis mellifera on artificial ‘Salvia’ flowers

•It is possible to train bees on artificial bilabiate flowers with a lever mechanism.•Bees learn to differentiate between models with and without internal barrier.•Force matters: bees recognise low forces of 2.8–3.8 mN.•Artificial flowers are suitable for further choice experiments, analysing cost-benefit ratio.

Many bee flowers demand physical force from their pollinators. An example is Salvia with lever-like anthers restricting access to nectar. Though the needed force is generally low, it is largely unknown how far even low forces affect flower preference and foraging behaviour of bees. In the present paper, we introduce a method to measure the response of bees to a force mechanism. We explain the construction of artificial flowers mimicking the lever mechanism of a Salvia flower and the procedure to train honeybees and bumblebees to the models. We document the behaviour of the bees on models without barriers and on those with low forces aiming at the same time to determine the bees’ sensibility for discriminating amongst slightly different flower constructions. Artificial flowers with and without movable levers are constructed to test the effect of a present or absent lever under standardised conditions. Both model types offer sugar syrup (37%) of the same volume. The lever force is 2.8–3.8 mN corresponding to the average force in bee-pollinated Salvia species. Choice experiments, five minutes each, are conducted with single bumblebees (lab, n = 40) and honeybees (outdoors, n = 40). The animal's behaviour and visitation frequency, handling time and flight time between two flower visits are recorded and statistically evaluated. Both bee species can learn to handle the complex artificial flowers. They significantly prefer the model without any barrier indicating that they are able to discriminate amongst models without and with low force demands. The results clearly illustrate that the artificial flowers are suitable for experiments. Continuative choice experiments with reciprocal models of nectar concentration and force will provide a deeper insight into the cost-benefit ratio by bees.