Abstract
The timing of volatile organic compound (VOC) emission by flowering plants often coincides with pollinator foraging activity. Volatile emission is often considered to be paced by environmental variables, such as light intensity, and/or by circadian rhythmicity. The question arises as to what extent pollinators themselves provide information about their presence, in keeping with their long co-evolution with flowering plants. Bumblebees are electrically charged and provide electrical stimulation when visiting plants, as measured via the depolarisation of electric potential in the stem of flowers. Here we test the hypothesis that the electric charge of foraging bumblebees increases the floral volatile emissions of bee pollinated plants. We investigate the change in VOC emissions of two bee-pollinated plants (Petunia integrifolia and Antirrhinum majus) exposed to the electric charge typical of foraging bumblebees. P. integrifolia slightly increases its emissions of a behaviorally and physiologically active compound in response to visits by foraging bumblebees, presenting on average 121 pC of electric charge. We show that for P. integrifolia, strong electrical stimulation (600–700 pC) promotes increased volatile emissions, but this is not found when using weaker electrical charges more representative of flying pollinators (100 pC). Floral volatile emissions of A. majus were not affected by either strong (600–700 pC) or weak electric charges (100 pC). This study opens a new area of research whereby the electrical charge of flying insects may provide information to plants on the presence and phenology of their pollinators. As a form of electroreception, this sensory process would bear adaptive value, enabling plants to better ensure that their attractive chemical messages are released when a potential recipient is present.
Highlights
Olfaction is generally considered to be pivotal in underpinning plant-pollinator communication
To prepare headspace extracts for gas chromatography (GC) and GC-Mass Spectrometry (GC-MS) analyses, the flowers were individually enclosed in roasting bags (28cm × 30cm; Sainsbury's Supermarkets Ltd, UK), which were connected with a charcoal-cleaned air source, supplying an inflow of 600 mL/min
The volatile emissions of P. integrifolia flowers was significantly increased when touched with a 600-700 pC ball (Fig. 2a), whilst no increase was seen from flowers touched with the grounded control rod
Summary
Olfaction is generally considered to be pivotal in underpinning plant-pollinator communication. In some flowering plants, such as Antirrhinum majus, rhythmic scent emission persists in continuous light or dark conditions suggesting an endogenous rhythm independent of environmental influence (Kolosova et al 2001). This is presumed to improve synchronicity between plants and pollinators (Bloch et al 2017), yet sole reliance on an endogenous rhythm could allow VOC emissions when pollinators are absent, such as during rain or poor
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