During summer the Arctic is buzzing with insects. Here like everywhere else plants rely on them for pollination. A new study found that small flies related to the common house fly are the most important insects in the Arctic. This findings, however, offers cause for concern, as arctic fly abundances are declining as the Arctic continues to warm.
Researchers from Finland, Sweden, Denmark and Canada wanted to find out which inset is the most important pollinator in the Arctic. For their research they focused on a common Arctic plant: the Mountain avens (Dryas). They first recorded at 15 different sites in northeast Greenland which insects visited the flowers and then returned to score the seed set of these flowers. The results were clear, the more flies were present, the more flowers set seed. The flies (family Muscidae) are similar to our house flies. Within this family, however, one species stood out. What best explained seed set was the abundance of a single fly, Spilogona sanctipauli.
To record the insects visiting a plant, the researchers invented a new solution. "Instead of observing flowers for hours and waiting to see which insect visited them, we constructed self-trapping flowers", explains Mikko Tiusanen, lead author of the study. "We used something very similar to fly paper – the sticky traps used to catch insects in green-houses. In our case, we cut this sticky paper into natural-looking flowers, and hid them among the real flowers."
As a second methodological innovation, the researchers decided not to rely on external characters to identify their catch, but on DNA markers. "Having all 8,500 insects we caught identified by experts around the world would realistically have taken years – and been impossible for part of the catches", explains Mikko Tiusanen. "Overall, our methods proved highly efficient", says his collaborator Tomas Roslin. "Where previous, intensive studies in the same region had recorded 30 insect species on the flowers of avens, we found a 177 species. That means that two-thirds of all insect species known from the area will actually visit this flowering species – showing just how important this single plant species is to the whole ecosystem. This overall diversity of flower visitors makes it even more surprising that a specific group of flies, and even a single species among these flies, turns out so important for the seed set of the plant."
While the current findings are exciting, they also raise concern. The fly which was found to be so important for avens are now declining in the region. Part of this decline may be due to an increasing temporal mismatch between flies and their flower resources. In support of this interpretation, the researchers recorded what insects visited avens flowers early compared to late in the season, i.e., during peak flowering versus later, when there are less flowers in bloom. Surprisingly, they found that more insects visited the late flowers. "Again, this is really quite worrying", explains Niels Martin Schmidt, the head of Zackenberg research station where the study took place, "as in the warming Arctic, flowering time is getting earlier and earlier, whereas insects show less of a change. Hence, we actually see the timing of avens sliding into the early summer when less flies are there to service the flowers. For the plant, this means less pollinators, and for the flies, this means less food. If this rift expands, then this may threaten Arctic pollination."
But the researchers also faced challenges during their study. Mikko Tiusanen recalls, "If there is one Arctic animal which really didn’t help us, it was the muskoxen. They will come grazing wherever there are Mountain avens. And when the muskoxen come munching, we retreat – but after their visits our sticky flowers will be all covered in hair and trampled."
"The other arctic animal harassing us were the snow buntings", adds Tomas Roslin. "Some of them will be just all too happy to eat the flies off our flower traps. But here again we benefitted from DNA testing rather than taxonomy. As long as a single leg remained of an insect, we could identify it."
Source: Swedish University of Agricultural Sciences