Interview with Emmanuelle Porcher
Emmanuelle Porcher has been Director of the Centre d'écologie et des sciences de la conservation since 2020. Winner in 2020 of the Recherche prize from the French Society of Ecology and Evolution, she has been invited to occupy the annual Biodiversity and Ecosystems chair at the Collège de France for the year 2023-2024. She looks back at the research challenges we face in the face of the decline of pollinators and all the ecosystems of which they are a part.
What do we know today about the decline of pollinating insects ?
Emmanuelle Porcher : The few studies carried out on the subject conclude that between two thirds and three quarters of the insect population have disappeared in the space of just a few decades. These figures come from two well-documented examples, which have caught the attention of the research community. In Germany, a naturalist association used identical traps for around thirty years to regularly capture and weigh insect mass. Another study in the UK compared insect crushes on car license plates between 2004 and 2021. However, these studies remain on a localized regional scale, and do not allow these changes to be characterized on a global scale.
One of the hurdles we face today is highlighting this decline on a broader scale. To achieve this, we need to use standardized methods and do so over the long term. For example, in France, although the data sets in the collections of the Muséum national d'histoire naturelle are highly accurate in terms of species identification, they are based on observations collected in a heterogeneous way over the years. Their use to assess insect decline therefore proves difficult, despite our impression of knowledge. Statistical analysis tools exist to take account of this heterogeneity, but their effectiveness remains poorly understood. The summaries available on a global scale therefore diverge due to the heterogeneity of the data : some report a rapid decline in insects, others detect no problem, and some even mention an increase in certain environments.
In this context, participatory science may, at first glance, appear to be an epiphenomenon. In reality, they completely change the dimension of our research in the natural sciences by considerably increasing the scale of measurements, while relying on a single, standardized protocol. Instead of relying solely on one researcher to collect these data, several hundred citizens report the same information, ensuring consistency in the data collected. At the Muséum national d'histoire naturelle, the Vigie-Nature participatory science program, in place since 1989 for birds, has been studying pollinating insects in particular, as well as plants pollinated by them, for some fifteen years. In France, much of what we know about changes in biodiversity in recent years comes from participatory science.
We hear a lot about the decline of insects. Are plants, which depend on insects, affected by this trend ?
They too are changing, albeit in different ways. For example, their flowers are smaller than they were a few years ago. To demonstrate this, Pierre-Olivier Cheptou, an evolutionary biologist from Montpellier, used an approach called " the ecology of resurrection ": he cultivated old pansy seeds and compared them with recent seeds from the same population. His findings are clear : plants now have smaller flowers than they did twenty years ago. This reduction can be explained by the diminishing presence of insect pollinators: when there are no more pollinators to attract, natural selection favors smaller flowers, which are less costly to produce.
It's important to understand that the main driving force behind pollination is insects. By drinking plants' nectar and eating their pollen, they find their source of food, and by transporting reproductive cells between plants, they guarantee the latter's reproduction. This co-benefit has favored, over the course of evolution, plants with characteristics attractive to pollinators. For example, we know that insects are attracted by yellow, blue and ultraviolet colors - hence the presence of flowers in these hues. It even happens that the same species of plant, depending on the population and the dominant pollinator, changes color. In California, for example, a coastal plant pollinated by hummingbirds has red flowers. Away from the coast, pollinated by a butterfly, it has yellow flowers.
As pollinators become rarer, plants can adapt by changing the way they reproduce. One possibility is to resort to self-fertilization, i.e. the reproduction of a plant with itself, without the need for pollinators. This is the case for certain cereal plants such as wheat. Self-pollinating wild plants, on the one hand, have smaller flowers and fewer resources for pollinators, and, on the other, are less adaptable to changes in their environment. We are therefore entering a downward spiral : there are fewer and fewer plants with large flowers that are attractive and nourishing for pollinators, which contributes to a decline in populations and favors the evolution of plants towards even smaller, more self-fertilizing flowers. And in the long term, these will not adapt very well to environmental variations, such as climate change. There is therefore a risk that a large number of plant species will disappear.
What impact do these changes have on pollination and, more broadly, on agricultural production ?
It's likely that pollination is becoming less and less efficient, but we lack the long-term measurements to prove it. This is precisely one of the areas I'm working on. Nevertheless, some studies suggest that the yields of crop species that rely heavily on pollinators have declined in recent decades. Take the example of almond trees : the quantity of almonds produced per hectare is declining worldwide due to less efficient pollination. However, global demand for this product remains constant or is even increasing, prompting growers to plant larger areas. Today, there are even companies offering pollination machines ! These machines, in the form of large tractors, spray pollen into the fields. The case of almond trees is not unique. In Burgundy, producers of blackcurrant liqueur are experiencing serious production problems. Ecologist Marie-Charlotte Anstett has demonstrated that the introduction of a large number of bumblebees around blackcurrant plants doubles or even quadruples blackcurrant production, enabling farmers to generate up to 15 000 euros in additional profits per hectare.
The decline in insect numbers and pollination potential is also having an impact on our food supply. One third of the total volume of agricultural production and a significant proportion of the vitamins essential to our diet depend on pollinators. For example, 98 % of naturally-occurring vitamin C production comes from plants such as citrus fruits, which require insect pollinators.
What solutions can we envisage to better protect plants, pollinators and, with them, our agriculture ?
Generally speaking, we need to leave more room for wild life and its diversity. This means, of course, increasing the number of protected natural areas, but also making changes that enable wild species to cohabit with humans and their activities.
In agriculture, until now, the tendency has been to opt for fields containing only the cultivated species, using pesticides to combat weeds and species known as " crop pests ". A possible solution to avoid their use is to diversify the landscape by reintroducing hedges, small woods, ponds and permanent meadows. At the moment, in northern France for example, farmers can't do without pesticides, as there are no longer any natural elements in these agricultural landscapes that provide shelter for natural predators to control pests. Proposals have been put forward to make the return of these natural elements in agricultural landscapes compatible with the use of machinery. Some imagine configurations with elongated fields and just enough space to pass a combine harvester and hedgerows on either side to maintain high yields while reducing or even abandoning the use of pesticides. This is no pure fantasy : scenarios on a European scale have shown that using agroecology would be viable for our agriculture. As for the impact on wild species, current studies point to positive results. For example, in organically farmed fields, without pesticides or synthetic fertilizers, there are 50 % more individuals and 25 % to 30 % more wildlife diversity.
Fields aren't the only areas where we need to take action if we want to preserve biodiversity. Urban spaces also need to be developed accordingly. Some initiatives, such as the installation of honeybee hives in cities, have already been undertaken. This is a good idea in itself, but these bees do not always find sufficient food in urban ornamental plants. These plants have often been modified by human selection and are not always rich in resources. Some studies have also shown that a high density of hives can lead to competition between bees and wild pollinators, depriving the latter of food resources : it is therefore important to increase the diversity of wild plants, including in the heart of cities.
On a collective level, we'll need to review our standards when it comes to planning urban spaces. For example, unloved plants such as nettles, which are often kept out of green spaces, can be beneficial to many caterpillars and butterflies. Ivy, flowering in autumn when other resources are scarce, can be grown to support bees, saving them from winter feeding if they have stored enough honey from ivy around their hives.
Do you think that biodiversity is taken seriously enough in current policies ?
Given today's issues, we need to go beyond the traditional image of the interaction between plants and pollinators. Flowers and butterflies are cute, yes. But it's crucial to understand that it's a complex system that serves as the foundation of the world we live in : we're only just beginning to grasp its inner workings, and the full complexity still eludes our understanding. This has direct implications for us humans.
It's possible that what we consider insignificant is actually very important, and that at a certain threshold, this system will undergo a radical transformation, with repercussions not only on our food resources, but also on the quality of our environment. As far as the biodiversity crisis is concerned, perhaps we haven't yet fully grasped the scale of the problem.
Interview by Emmanuelle Picaud
