The most extreme and unpredictable climate episodes can collapse populations of common insects such as butterflies

Two new studies led by CREAF researcher Maria Vives-Ingla note that microclimates in forests - areas with a temperature, shade or humidity different from the environment - can alleviate the growing impacts of climate change, for example, by providing conditions of lower temperature and higher humidity. However, despite this data, the team has also found that if the worst future warming scenarios are fulfilled and the frequency of rarer and more intense weather phenomena increases (such as heat waves exceeding 40°C combined with drought) the 'rules of the game' change and there could be an alarming decline in insects, where even these climate refuges could lose their protective effect. The research was carried out with the fragrant white butterfly (Pieris napi), but according to the team the results could be extrapolated to other butterflies and insects.

In 4 intensive years of research, the MICROCLIM project team has published a study in Ecological Monographs that shows that butterfly larvae have a different survival rate depending on the microhabitat where they are laid and developed. This article was published in the initial phase of the project. The same team has also published a more recent study in Global Change Biology that shows a generalized decline in butterflies in future scenarios whith extreme phenomena. "These projections show that microclimatic shelters can offer temporary protection, but do not guarantee long-term resilience in the face of the most extreme and unpredictable phenomena," explains Maria Vives-Ingla, first author of the publications within the framework of her thesis.

To carry out the studies, they have combined environmental sensors with mathematical models, as well as field and laboratory work. Among other authors and entities, the research also involved Jofre Carnicer, researcher at the Institute for Research in Biodiversity (IRBio-UB) and professor of Ecology at the University of Barcelona (UB), affiliated with CREAF and also director of Maria's doctoral thesis, and Constantí Stefanescu, researcher at the Granollers Natural Sciences Museum, affiliated at CREAF and coordinator of the Catalan Butterfly Monitoring Scheme (CBMS), a butterfly monitoring network that has collected more than 30 years of data throughout Catalonia.

More specifically, the article published in Ecological Monographs shows that the choice of microhabitat by insects can determine their survival in the face of heat waves. The research was carried out with two species of butterflies common in Catalonia, the fragrant white (Pieris napi) and the cabbage white (Pieris rapae), which despite using the same plants to feed and lay eggs, select very different microenvironments: shaded areas in the case of the fragrant white and open, sunny areas in the case of the cabbage white, which can experience a temperature difference of between 3-10ªC, between the shaded and sunniest areas. The result is that Pnapi butterflies, which choose more shaded areas, drastically reduce mortality due to extreme heat, “despite being more sensitive to heat in physiological terms”, explains CREAF researcher Jofre Carnicer. However, this thermal refuge comes at a cost: host plants in shaded areas can be scarce during summer droughts, which could endanger the availability of food for the larvae. "Therefore, we see that studying the impact of climate change at the microhabitat level is key", highlights the Jofre Carnicer.

In the second publication, the team focused on analyzing how the scented blanquette responds under scenarios without a drastic reduction in CO2 emissions where the average temperature of the planet increases by 2 to 4 ºC and there are more extreme phenomena that combine droughts and heat waves. The study was carried out with data from two protected Catalan locations with different environmental characteristics: El Cortalet, in the Aiguamolls de l’Empordà Natural Park, and the Can Jordà forest, in the Garrotxa Volcanic Zone Natural Park.

Under the current scenario, the results showed that the population in Empordà decreased by 3% per year, while in Garrotxa it experienced a growth of 6% per year. “This difference is explained by the forest microclimate that acts as a climatic refuge in the forest of Can Jordà de la Garrotxa, which protects the larvae of the first stages from extreme heat and food shortages”, explains Constantí Stefanescu. However, under a scenario of “combined or multiple events”, the models indicate that this protective effect disappears and there is an alarming decline in butterflies. “Mathematical simulations carried out in shaded microenvironments indicate that just two days a month with temperatures above 40°C in summer would be enough to cause negative growth rates in La Garrotxa and, if this temperature coincides with summer drought, the decline would be even worse”, warns Constantí Stefanescu.

“In addition, we also found that there is a great sensitivity of small larvae to heat waves and severe droughts, especially when these events are combined. What we have discovered with the fragrant whitefly, a model species that is intensively studied in many universities in Europe, allows us to describe the basic processes that produce climate impacts on natural insect populations. These are processes that, once scientifically described, can then be extrapolated to other common insects for which we do not have as much information, as long as they have a similar biology and natural history”, adds Jofre Carnicer. If this trend of a greater impact of extreme phenomena becomes a reality, essential natural functions could be affected, such as plant pollination or food for other animals that depend on these insects to survive.

To make the predictions, the team has developed a population matrix model (MPM) based on data from the Catalan Butterfly Monitoring Program, previous studies and laboratory experiments. This model allows us to simulate the entire life cycle of the fragrant white butterfly and predict how its population will respond to different climate scenarios and at all growth stages. Specifically, they have simulated 10,000 scenarios with different levels of warming and frequencies of extreme episodes. “We believe that this tool has great value for understanding the real impact of climate change on biodiversity, although it can still be improved with more detailed biological data, such as fecundity”, concludes Maria Vives-Ingla.

The article published in Global Change Biology is also signed by researchers from the University of Bristol Chris Clements and Pol Capdevila, also from the UB. Regarding the research published in Ecological Monographs, UB researchers Armand Casadó-Tortosa and Meritxell Garcia, Javier Sala, researcher at the Museo Nacional de Ciencias Naturales of the CSIC and Josep Peñuelas, researcher from the CSIC at CREAF, have also participated. The research of the MICROCLIM project (2020-2024) will continue within the framework of the new ECO-FUN project (2024-2027) of the CREAF, which, collecting all the knowledge accumulated in these articles and research, will design microclimatic and physiological monitoring systems for ecosystems impacted by extreme effects of climate change based on the emerging technology of the Internet of Things (IoT), both projects led by Jofre Carnicer.

Reference articles: 

• Vives-Ingla, M., Sala-Garcia, J., Stefanescu, C., Casado-Tortosa, A., Garcia, M., Peñuelas, J., & Carnicer, J. (2023). Interspecific differences in microhabitat use expose insects to contrasting thermal mortality. Ecological Monographs, 93, e1561. https://doi.org/10.1002/ecm.1561.
• Vives-Ingla, M., Capdevila, P., Clements, C. F., Stefanescu, C., & Carnicer, J. (2025). Novel regimes of extreme climatic events trigger negative population rates in a common insect. Global Change Biology, 31(4), e70148. https://doi.org/10.1111/gcb.70148