A red mason bee (Osmia bicornis) in its winter quarters, a reed stalk. It has just hatched and is preparing to leave the nest.
Photo Credit: Cristina Ganuza / Universität Würzburg
Scientific Frontline: Extended "At a Glance" Summary: Climate-Induced Phenological Shifts in Bees and Wasps
The Core Concept: Rising global temperatures cause wild bees and wasps to emerge prematurely from winter dormancy, leading to a detrimental depletion of essential energy reserves before food resources become available.
Key Distinction/Mechanism: Unlike typical emergence which is ecologically synchronized with floral blooming, heat-triggered premature emergence forces insects to metabolize crucial fat reserves rapidly. The mechanism distinctly impacts populations based on their geographic origin; spring-emerging insects from cooler climates are the most vulnerable, experiencing up to a 34% loss in body mass when exposed to warmer spring conditions.
Major Frameworks/Components:
- Controlled Climate Rearing: Simulating exact temperature gradations to isolate the physiological impacts of varying spring climates on overwintering insects.
- Phenological Mismatch Theory: Examining the ecological asynchrony that occurs when pollinator emergence outpaces the seasonal availability of essential floral resources and prey.
- Bioclimatic Origin Analysis: Correlating an insect's adaptive resilience to the historical temperature baseline of its native habitat (cooler vs. warmer regions).
- Physiological Fitness Metrics: Utilizing body mass retention and energy reserve depletion as primary quantifiable indicators for survival and reproductive viability.
Branch of Science: Ecology (Animal Ecology), Zoology, Phenology, and Environmental Science (Climate Change Biology).
Future Application: The data can be integrated into predictive ecological models to forecast regional pollination deficits in agriculture. Furthermore, the findings will inform targeted conservation and habitat management strategies to protect vulnerable pollinator populations against increasing extreme heat events.
Why It Matters: As keystone species for ecosystem stability, the declining physical fitness and reduced reproductive capabilities of wild bees and wasps directly threaten biodiversity. Their inability to adapt rapidly to warming temperatures poses a cascading risk to global agricultural productivity and food security.
A large-scale experiment shows: Heat brings bees and wasps out of hibernation earlier – many of them then have worse starting conditions. This is especially true for species in cooler regions that hatch in spring.
Most wild bees overwinter as pupated larvae in their cocoons in the soil, wood, or other protected places. Species that hatch in early spring overwinter as fully developed adults in the cocoon. On the other hand, species that hatch in summer still must complete their development in spring.
Globally, climate change is changing the timing of insects emerging from hibernation in spring or summer. These shifts can have consequences: if insects hatch too early due to higher temperatures, they may not yet find the flowers or prey they feed on. They also burn their vital fat reserves more quickly at higher temperatures, which can reduce their chances of survival and reproduction.
Insects from 160 locations in Bavaria examined
What about the physical fitness of bees and wasps when temperatures change around the time of hatching? This has a team around Dr. Cristina Ganuza and Professor Ingolf Steffan-Dewenter examined by the Biozentrum of the University of Würzburg. The researchers examined five wild bee and wasp species that occur in Bavaria and hatch at different times of the year.
For the study, the team set themselves a mammoth task: They collected almost 15,000 hibernating individuals from over 160 regions in Bavaria and then raised them at the university under controlled cold, warm and hot spring conditions to recreate different climate scenarios.
Females lose up to 34 percent of their body mass
All five species hatched earlier in warmer spring temperatures. However, populations differed according to their climatic origin: Spring species from warmer regions such as Lower Franconia appeared particularly early in warm spring temperatures and retained more body mass in the subsequent period than individuals from cooler regions such as the Bavarian Forest.
In contrast, in late summer species, only individuals from cooler regions hatched earlier. Females of summer species lost body mass more quickly under warmer conditions – in some cases up to 34 percent.
Insects from cooler regions that fly in spring have disadvantages
"Our data show that insects from cooler regions are particularly vulnerable to warm springs. They lose their energy reserves faster and therefore have worse starting conditions", says Dr. Cristina Ganuza. The first author of the study conducts research at the Chair of Zoology III (Animal Ecology and Tropical Biology) at the University of Würzburg.
The results of the study are in the Journal of Functional Ecology published. They are part of the LandKlif project led by Professor Steffan-Dewenter in the Bavarian Climate Research Network (bayklif).
The researchers see several open questions, which need to be clarified next:
- How do extra extreme heat days affect hatching?
- What are the consequences of the insects' energy reserves for their pollination performance?
- How quickly can populations adapt to changing temperatures?
Published in journal: Functional Ecology
Authors: Cristina Ganuza, Sarah Redlich, Andrea Holzschuh, Thomas Hovestadt, Oliver Mitesser, Sebastian Göllner, Annika Klein, Tamara Summ, and Ingolf Steffan-Dewenter
Source/Credit: University of Würzburg | Robert Emmerich
Reference Number: eco041326_01