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Flower shape influences parasite transmission to bees

The spread of various parasites is one of the main drivers of population decline in both managed and wild bees. Many of these parasites are transmitted by the shared use of flowers, turning these major sources of nourishment into potential disease hotspots.

A new study led by the North Carolina State University has found that the shape of flowers has the biggest effect on how parasites are transmitted to bees. According to the experts, such findings may help stakeholders plant flowers that are less dangerous for pollinators.

The scientists examined the common eastern bumblebee (Bombus impatiens) and a gut parasite called Crithidia bombi in order to clarify how flower traits, such as the size, shape, and number of flowers, played roles in three steps that usually lead to parasite transmission from flowers to bees: feces deposition on flowers, survival of the parasite on flowers, and the acquisition of the parasite by a new bee host.

“Of the flower traits we measured, floral shape was the best predictor of parasite transmission to bees,” said study lead author Mario Simon Pinilla-Gallego, a former doctoral student in Applied Ecology at NC State University.

“Wide and short flowers – like black-eyed Susans and coneflowers – reduce the survival of the parasite on flowers, but at the same time they collect more bee feces, and bees are more likely to come in contact with and acquire the parasite on these types of flowers,” explained study senior author Rebecca Irwin, a professor of Applied Ecology at the same university.

Identifying floral traits and flower species which have lower rates of parasite transmission to bees could help stakeholders select flower mixes that promote bee health, while offering them the floral resources they need.

In future research, the scientists aim to take into consideration other factors, such as how often and how long bees visit flowers, the behavior of bees while foraging, and environmental factors which could change the effects of particular floral traits.

The study is published in the journal Ecology.   

By Andrei Ionescu, Staff Writer

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