Plant Guttation Droplets

Plant guttation, a fluid from xylem and phloem sap secreted at the margins of leaves from many plant species, serves as a reliable and nutrient-rich food source for many insects, including bees, wasps and flies, according to new research by scientists from Rutgers University, the Instituto Valenciano de Investigaciones Agrarias and Universitat de Valencia.

Guttation droplets are an important but underexplored feature in plants, with profound implications for insects in agricultural and natural ecosystems. Image credit: Pablo Urbaneja-Bernat.

“Our study shows for the first time that plant guttation is a nutrient-rich source of food for insects,” said Professor Cesar Rodriguez-Saona, a researcher in the Department of Entomology in the School of Environmental and Biological Sciences at Rutgers University-New Brunswick.

“Many insects such as bees, wasps and flies drink the small droplets, which arise on nights with high levels of moisture in soil, and biologists considered them only as a source of water for insects.”

“But the droplets are rich in carbohydrates and contain proteins that are essential for many insect species.”

Until this study, the benefits of guttation to insects were unknown. To address this gap, Professor Rodriguez-Saona and colleagues assessed the fitness of an insect herbivore (Drosophila suzukii), a parasitic wasp (Aphidius ervi) and a predatory insect (Chrysoperla rufilabris) when they had access to guttation drops in highbush blueberry fields.

The insects increased their longevity and fecundity when fed on these guttation droplets compared to those fed on control water.

The droplets were also present through the entire season and their presence doubled the abundance of beneficial insects — parasitic wasps and predators — that protect plants from pests.

As a result, droplets might reduce the many problems caused by pests in crops, including invasive pests.

And the researchers suggest that might occur in numerous crops where the droplet phenomenon is common, such as rice, wheat, barley, rye, oats, sorghum, corn, tobacco, tomatoes, strawberries and cucumbers, among others.

“These findings are important for the conservation of beneficial insects because they can find and feed on droplets when pollen, nectar, hosts or prey are scarce,” Professor Rodriguez-Saona said.

“Overall, the results demonstrate that the droplet phenomenon is highly reliable, compared with other plant-derived food sources such as nectar, and it increases the communities and fitness of insects,” the scientists said.

The study was published in the Proceedings of the Royal Society B: Biological Sciences.

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Urbaneja-Bernat Pablo et al. 2020. Plant guttation provides nutrient-rich food for insects. Proc. R. Soc. B 287 (1935): 20201080; doi: 10.1098/rspb.2020.1080