A new study highlights potential causes for changing foraging habits of bumblebees. Using advanced molecular techniques called pollen metabarcoding, researchers investigated interactions between bumblebees and plants in Cuxhaven, Germany, and how they changed over 60 years. Their findings can help us understand the connections between availability of floral resources and changing landscapes.
The study, led by the Botany Department of the University of Kassel (Germany) in collaboration with the Leibniz Institute for the Analysis of Biodiversity Change (Germany), used bumblebee specimens from historical museum collections dating back to 1968/69 and compared them with bumblebees collected in the field in 2019. By analyzing pollen samples attached to the bodies of the bees, the researchers were able to identify the plant species they had interacted with.
The results revealed significant shifts in the foraging habits of bumblebees between the late 1960s and more recent sampling periods. In particular, there was a noticeable decrease in interactions with Fabaceae plants in 2019 compared to the past. “This suggests that changes in the landscape have led to alterations in the availability of floral resources, which may contribute to the decline of specialized bee species,” the researchers explain.
“The successful application of scalable molecular techniques to analyze historical pollen samples highlights the value of museum collections as a valuable resource for biodiversity research,” they add. “This study, published in the journal Metabarcoding and Metagenomics, serves as a proof of concept for comparative analysis of recent and historical pollination data, providing important insights into the changes in foraging trends of bumblebees over time.”
“In conclusion, this study contributes to our understanding of bumblebee interactions with foraging resources and the impact of landscape changes on their foraging habits,” say the researchers. Their findings underscore the importance of conserving and restoring suitable habitats for pollinators.
“Future research in this field is expected to provide valuable insights for the conservation and management of pollinators and their critical role in maintaining ecosystems,” they conclude.
Original source:
Kolter A, Husemann M, Podsiadlowski L, Gemeinholzer B (2023) Pollen metabarcoding of museum specimens and recently collected bumblebees (Bombus) indicates foraging shifts. Metabarcoding and Metagenomics 7: e86883.https://doi.org/10.3897/mbmg.7.86883
Images by Andreas Kolter
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Sycamore maples destroyed by the Sooty bark disease. Photo by Dr Miloň Dvořák
Especially after the last few COVID-affected years, nobody doubts that emerging infectious diseases can threaten the whole world. But humans are not the only ones at risk! With intensive global trade, many tree parasites are accidently introduced to Europe in packaging or directly on goods. Traveling in the wood, on plants or in the soil of their pots, they can remain undetected for a long time.
“Forms of life of parasitic fungi are extremely diverse and very often practically invisible,” says Dr Miloň Dvořák of the Department of Forest Protection and Wildlife Management at Mendel University in Brno, Czechia. “An infected tree may look completely healthy for some time, which complicates the control of the disease enormously. It reminds me of the ancient Trojan Horse, where European trees are so surprised, defenceless, and later defeated, like the Trojan warriors.”
How can an infected tree look healthy and then suddenly get sick? “Like in the human body, in trees too, the trigger can be stress,” explains Dr Dvořák. The tolerance of trees to a pathogenic fungus turns lower under the conditions of changing climate and so the tree starts to die of the disease.
One typical example of such a disease is the Sooty Bark Disease (SBD) on maples, caused by a microscopic fungus called Cryptostroma corticale. “The fungus was probably introduced to Europe during the Second World War and for the rest of the 20th century we did not hear much about it,” says Dr Dvořák.
Sooty Bark Disease (Cryptostroma corticale) on Sycamore. Photo by gailhampshire used under a CC BY 2.0 license
The situation has changed and over the last twenty years the fungus has been reported more and more often. After dry and hot periods, the trees start to die of the infection, which is accompanied by the creation of brown-black masses of “soot” under the peeling bark of the maples.
The “soot” is in fact spores, which help the fungus spread and infect other trees. It is harmful for wounded trees, but it can also cause hypersensitivity pneumonitis in humans.
So, the species became a target for a group of phytopathologists gathered by an European HORIZON 2020 project entitled “Holistic management for emerging forest pests and diseases (HOMED)”. Scientists from six countries (Czechia, France, Italy, Portugal, Sweden and Switzerland), including Dr Dvořák, decided to develop a precise, DNA based (real-time PCR) diagnostic method to detect and monitor the pathogen in air samples. They published their method, the outcomes of its use, and their new findings about SBD epidemiology in the open-access journal NeoBiota.
Volumetric air sampler installed in Brno, Czech Republic, sampling pollen for allergen forecast. Photo by Aneta Lukačevičová
How to look for DNA in air samples? Simple devices called volumetric air samplers can suck the air against a piece of sticky tape, where every particle gets stuck and can be analyzed. “These devices are not really cheap, moreover, they demand regular maintenance,” explains Dr Dvořák. “But, actually, they are in common and regular use in the whole of Europe – remember the weather forecast, particularly that part about the “pollen report” for allergic people. This forecast is based on data of more than 600 stations united by the European Aeroallergen Network (EAN). Every station permanently maintains one volumetric air sampler and keeps an archive of the samples.”
The HOMED team got in contact with their national EAN collaborators and processed their samples with molecular techniques (real-time PCR).
Thanks to this sensitive detection method, the survey among samples was very successful. The “sooty” fungus was found in air samples from countries where the disease has been reported, and, in a more detailed study in France, the pathogen was found in the air 310km from currently diseased trees! This result suggests that the fungus can disperse long distances by wind.
Black stromata – source of billions of hyper-allergenic spores. Photo by Dr Miloň Dvořák
“Our results show that the SBD disease is at an exponentially increasing phase in France and Switzerland with an increase in the magnitude of the number of disease cases that peaks following a marked water deficit,” the researchers write in their study. They hope that early aerial detection of C. corticale in disease-free countries could help implement more efficient measures for SBD detection and eradication in the field.
“This European experiment fully confirmed the potential of this approach to monitor the pathogen’s outbreaks in early stages of its spread,” concludes Dr Dvořák.
Research article:
Muller E, Dvořák M, Marçais B, Caeiro E, Clot B, Desprez-Loustau M-L, Gedda B, Lundén K, Migliorini D, Oliver G, Ramos AP, Rigling D, Rybníček O, Santini A, Schneider S, Stenlid J, Tedeschini E, Aguayo J, Gomez-Gallego M (2023) Conditions of emergence of the Sooty Bark Disease and aerobiology of Cryptostroma corticale in Europe. In: Jactel H, Orazio C, Robinet C, Douma JC, Santini A, Battisti A, Branco M, Seehausen L, Kenis M (Eds) Conceptual and technical innovations to better manage invasions of alien pests and pathogens in forests. NeoBiota 84: 319-347. https://doi.org/10.3897/neobiota.84.90549
