The effects of climate change on pollinators

Which animals fascinate you the most? There are probably lots of them, but some of them are definitely bees and butterflies. These insects are pollinators, creatures crucial to the health of our planet. Indeed, thanks to their uninterrupted flying from flower to flower, they are able to transfer pollen, thus helping plants to reproduce and grow by absorbing carbon dioxide. Pollination is an essential ecosystem service that maintains and promotes biodiversity. Most insects, in fact, are considered essential for the reproduction of about 75% of the plants that humans grow for their food needs. But there is a problem: with the climate change these insects, which are crucial for ecosystems and for humans, are seriously threatened, in some cases risking extinction. The causes are manifold and may involve the insects directly or indirectly the plants they visit. Let us see how.

The first effects of climate change on pollinators are related to both the physiological and morphological change of insects. For example, for some pollinators, above-average high temperatures speed the development of larvae. This may lead to the premature exit of the adults from the nest at a time when they cannot find anything to feed on, leading them, inevitably, to death. The result is a sharp cale of individuals of that species directly undermining its prosperity in a given range.

Another consequence of the increase in average seasonal temperatures is the reduction in body size. This stems from the fact that under these conditions the metabolic rate increases, consuming more energy. In addition, having small bodies with high temperatures helps to disperse body heat faster, preventing them from overheating. Indeed, during flight, most insects are able to regulate the temperature of their thorax to optimise muscle performance. However, if the temperatures of the environment around them are particularly high, the insects may not be able to decrease their body temperature quickly and may die.

The sucking mouthparts of pollinating insects are crucial for tapping into the nectar of flowers. Depending on the morphology of the flower, pollinators have developed in length this apparatus so as to be able to reach the precious nectar: however, a recent scientific article has shown that, with rising temperatures, the average length of this has decreased over the last 40 years. This could cause a morphological mismatch between pollinators and flowers with a certain conformation, with obvious consequences for insects that will find it increasingly difficult to feed and reproduce, undermining the prosperity of their own species.

Among the direct effects of climate change on insects, we have the alteration of behaviour. The optimal flight temperature of many insects is around 25°C, however, if it were to shift and stabilise above the average, both the distances travelled and the number of flights would decrease, reducing the number of flowers visited and, consequently, the valuable pollination service. Rising temperatures drive these insects to move to more comfortable habitats, preferring climatic zones compatible with their life cycle. Migration to cooler environments such as mountains is then observed. This often leads them to overlap their range with that of other species by competing for nutrient sources. Moving is not always possible: those already living in mountainous environments are not always able to seek refuge at higher altitudes. The worst consequence of being unable to cope with these new conditions is extinction.

plants also suffer from climate change. For example, in periods of high drought, nectar production and the sugar content in it are reduced to the detriment of pollinators. In addition, pollinators are attracted to flowers by complex smell signals consisting of mixtures of volatile chemical compounds that even humans can often pick up: as temperatures rise, their production and quality may decrease, impairing the flower's attractiveness and thus the risk of no longer receiving visitors. With above-average temperatures many plants tend to flower earlier, especially in spring. For some insects, there is a real risk that there is a mismatch between blooming and the start of their biological activity, thus finding themselves without food sources at the time of greatest need. Some studies speculate that 17-50% of pollinators will experience long periods of famine, leading to the decline of their populations.

As we have said, the pollinator insects are crucial: without them, many plants would lose the valuable pollination service that is crucial for their reproduction. This results in a very serious diversity loss at multiple levels that affects plants, pollinators and all organisms that feed on the products they generate. Identifying and promptly addressing these challenges will help mitigate negative impacts and avoid the catastrophic point-of-no-return scenario. It is therefore crucial to promote projects that support these species, such as the Biodiversity Oases of 3Bee that help maintain pollinator populations by providing them with nutritional resources. Another positive effect is the mitigation of climate change: in big cities, having more greenery helps to decrease heat islands, reducing the peaks of high summer temperatures as well as making the air cleaner and more breathable.

Article by Caterina Massa