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The role of floral scent in pollinator attraction

Scientists studied how the scents of a Solanaceae species vary and how they affect pollinator visitation and found that although floral perfume is an important factor, other signals might affect pollinators visits.

A new study published in AoB PLANTS by Mayumi Vega-Polanco and colleagues investigated how the scent of a buzz-pollinated Solanaceae species varies between populations in Mexico and the United States and found that although bees differentially visit plants of the different locations, floral extract alone cannot explain the differences in preference by bumblebees. The authors suggest that other factors, such as the presence of nectar or the colour of the flowers, may also play a role in pollinator visitation. 

The chemistry of floral scents acts as a powerful messenger, guiding pollinators towards their nectar-rich destinations. However, little is known about how variation in floral fragrances affects pollinator preferences. 

The research team, from ECOSUR in México, used a variety of methods to study the floral scent of Solanum rostratum (Solanaceae). They first extracted the volatile compounds from flowers of plants from both locations and they then used gas chromatography coupled with spectrometry (GC-MS) to identify and quantify the different compounds in the extracts. 

They found that the floral extracts from plants in the two populations contained 13 different volatile compounds that varied seasonally, with some of them such as methyl salicylate, being higher in the spring than in the fall. 

Interestingly, the relative abundance of these compounds varied between populations. For example, the extract from US plants contained higher levels of the compound benzyl acetate, while the extract from Mexican plants contained higher levels of methyl salicylate. 

Speed dating for Bumble Bees. Image: Vega-Polanco et al. 2023.

The research group then conducted two behavioural experiments to test how these differences in floral scent affected pollinator visitation. In the first experiment, they placed plants from both populations in a field cage and observed which plants were visited by bumble bees, Bombus impatiens. They found that bumble bees visited plants from the US populations more frequently than plants from the Mexican ones. 

In the second experiment, the researchers presented bumble bees with a choice between extracts from flowers of Mexican and US plants. They found that the bees showed no preference for either extract. 

The findings challenge the conventional wisdom surrounding floral scents and their sway over pollinators. The authors conclude:

“Although bumble bees visited plants from US populations more frequently than they did with plants from Mexican populations, we found no difference in the preference of B. impatiens for floral extracts. Other signals, besides floral volatiles, should be further evaluated to explain the pollinator preference for plants from US populations.” 

Vega-Polanco et al. 2023.

Vega-Polanco, M., Solís-Montero, L., Rojas,  J.C., Cruz-López, L., Alavez-Rosas, D., Vallejo-Marín M. (2023) “Intraspecific variation of scent and its impact on pollinators’ preferencesAoB PLANTS. Available at: https://doi.org/10.1093/aobpla/plad049 

Cover image: Bombus impatiens feeding on a coneflower. Photo: Canva.

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