Pollination: Fewer moths, more flies


Moths such as the reed owl (Plusia festucae) are rarer. © UFZ/ Wirestock_AdobeStock

Plants depend on the help of pollinators such as bees, moths or flies. But over the past century, scientists have found that the composition of pollinator communities in northern latitudes has changed. The insect species that dominate today may no longer perform their task as well as their predecessors, which could endanger plant pollination in the long term - especially against the background of advancing climate change.

Without animal pollinators such as bees or butterflies, many plants would not exist. Not only wild flowers, but also three quarters of the most important crops depend on the help of visitors to the flowers. Plants and their pollinators are intertwined in a sophisticated network. Some insects have even specialized entirely on individual plant species. Even small changes can therefore throw the pollination system out of balance in the long term.

Finnish forester as data collector

Researchers led by Leana Zoller from the Martin Luther University Halle-Wittenberg (MLU) have now used northern Finland as an example to examine how much pollinator communities have already changed over the past century. To do this, they first looked at historical data from the Finnish forester Frans Silén. Between 1895 and 1900, in the vicinity of the village of Kittilä – about 120 kilometers north of the Arctic Circle – he systematically surveyed which insects visited which flowers and how often.

Zoller's team then went looking for the places where Silén had already observed visitors to the flowers and collected new data as comparative values ​​for all 17 plant species that had been included in his survey at the time. Not much has changed in the area since Silén roamed the Finnish countryside. It is still sparsely populated and the land use is similar to that of yesteryear. Only climate change is now clearly noticeable there.

Climate change is bringing pollinators to their knees

Climate change appears to have had significant consequences for pollinators in the region, as comparison to then reveals drastic changes in insect community composition. Only seven percent of the observed flower visits involved the same insect and plant species as more than 100 years ago. According to the researchers, it is particularly worrying that there are far fewer insects today that have specialized in certain types of flowers. For example, the numbers of hoverflies and moths have fallen significantly, partly due to climate change. Since both specialists were particularly effective pollinators, their decline does not bode well, as the scientists suspect.

Instead, bumblebees and flies of the genus Thricops are the dominant flower visitors around Kittilä. They are not specialized in individual plants, but belong to the generalists among the pollinators. However, this means that they carry the pollen of all possible foreign plant species onto one and the same flower and are therefore possibly less efficient at their job than their predecessors. Nevertheless: "So far, the pollinator network in our study area still seems to be working well," says Zoller. "So far there is no evidence that the plants are getting too little pollen today and are therefore less able to reproduce." But that could perhaps change in the future. Even the flies, which have now taken over the pollinating job of moths and hoverflies, could eventually get too warm due to climate change. If they die in large numbers, there may be no one left to compensate for the dwindling pollinator network - and not only in Finland.

Source: Helmholtz Center for Environmental Research (UFZ), Article: Nature Ecology and Evolution, doi: 10.1038/s41559-022-01928-3

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