In recent years, the fundamental role of the bees as pollinating agents, especially for the benefit they bring to many crops.
A study by the Higher Council for Scientific Research (CSIC) has shown that mining bees of the genus Andrena, the main pollinators at the beginning of spring in the mountain ranges of the south of the Iberian Peninsula, they are particularly vulnerable to heat.
The work is published in the journal Ecological Monographs and is part of the European project Sumhal (Sustainability for Mediterraean Hotspots in Andalusia integrating LifeWatch ERIC), which aims to contribute to the conservation of the biodiversity in the western Mediterranean.
The prevalence of early-blooming mining bees in mountains is linked to their thermal biology.
In Spain there are more than 1,100 species different from bees. These have very different characteristics, which means that certain groups are more or less frequent at different times of the year and many of them can only be seen in environments with particular conditions.
The research led by the Doñana Biological Station (EBD-CSIC) would indicate that the prevalence of mining bees in the early bloom in Mediterranean mountain habitats in southeastern Spain it is favored for its thermal biology.
“In the mountain systems of the south of the Iberian Peninsula, most of the plants that flower at the end of winter or beginning of spring have Andrena as the main pollinators,” he points out. Carlos HerreraCSIC researcher at the EBD-CSIC and the Sumhal project.
Many of the species in this genus are specialists and only collect pollen from one plant species or from a small group of related species. Therefore, in mediterranean environments where the richness of plants is high, there is also a high diversity of species of this group of insects.
Very few Andrena species are able to substantially raise their temperature
In the Sierra de Cazorla (Jaén), the region where the study is focused, their importance as pollinators has been detected, for example in cruciferous such as fleshy Iberis (100 %) or Draba hispánica (71 %) and in bulbous plants such as Crocus nevadensis (79 %), Narcissus hedraeanthus (67 %) and Fritillaria lusitanica (63 %). However, its importance becomes zero or very low in species that flower in late spring or during summer.
The warmth of the flowers
The researchers contemplated several reasons to explain why Andrena bees prevail during the early period of the flowering season in these habitats: weak or no ability to heat above room temperature, a relatively low upper limit of thermal tolerance or a weak thermoregulatory capacity, among others.
“After studying the flower temperatures in those that forage we find that they are rarely above 21°C. However, bees of other genera also present in the region frequently feed on flowers with temperatures above 30°C”, points out the main author.
The data from the work, collected between 1997 and 2022, also clarify that there are very few Andrena species capable of substantially raising their temperature above ambient temperature. And if the body temperature rises above 30-31°C they need cool downmodifying their behavior to achieve it.
The CSIC researcher points out that “this suggests that if the climate continues to vary in our region, as shown by the series of recorded data and predicted by probabilistic models, increasing both the average temperature and the frequency of warm days, the suitable period of time for feeding these medium-sized bees will be substantially reduced” .
Carlos M. Herrera, et al. “Seasonality of pollinators in Mediterranean montane habitats: cool-blooded bees for early-blooming plants”. Ecological Monographs (2023)
Rights: Creative Commons.