Insect relic discovered from primeval forest times

Rare hoverfly in the nature reserve Saalberghau near Dessau

Brachyopa silviae (Tree Sedge Fly) © Umweltforschungszentrum Leipzig-Halle
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Scientists at the Leipzig-Halle Environmental Research Center (UFZ) have discovered a new insect near Dessau. It is an extremely rare hoverfly of which only six are known worldwide.

"The discovery of a still unknown animal species in the heart of Germany underlines the importance of biodiversity research in Germany, " says Frank Dziock of the Department of Conservation Research of the UFZ. The new species Brachyopa silviae (Silvias tree fly) belongs to the genus of tree osis, of which only 13 species are known in Europe. Their larvae feed exclusively on bacteria and other microorganisms in the sap of trees. These are caused by bark injuries and are most common on very old trees. The scientists therefore demand that even in managed forests, individual trees naturally age and die, so that such species have a chance to survive.

Unruly research objects

"If we researchers go into the forest, then we would have to actually have the nose of such a fly, in order to find the mucus flows under the tree barks, which are often not to be seen." Those like Dziock with Baumsaftschwebfliegen busy, which can not be easy Lay in a lush flower meadow and wait, what comesummummt comes. Because these insects live hidden within the woods on very old trees. They live on microorganisms that only occur in tree sap - in contrast to their better known relatives. Although many of these hoverflies are mistaken for wasps because of their black and yellow pattern, they can not sting. Their larvae are also very useful as they kill large numbers of aphids. In total, around 450 hoverfly species live in Germany with a wide variety of diets.

Almost overlooked sensation

For twelve years Dziock has been involved with the wildlife of the alluvial forests. For the first time, the 35-year-old biologist has succeeded in doing what every insect researcher has dreamed of: the discovery of a new species. At the same time, the catch that entered the network in the Saalberghau nature reserve on the Elbe near Dessau did not seem very spectacular. As part of a research project, the scientist had set up an insect trap to determine how hoverflies react to flooding. In this case, the insects serve as bioindicators. The contents of the trap looked normal at first glance.

"At first we thought, in a familiar way. Then we discovered that the two tiny dots on the backs of the flies were clear evidence of an as yet undiscovered species, " says Dziock. Looking closer at the seven-millimeter fly under the microscope, it turned out that your physique does not look like any of the known species. display

"That's why I borrowed the type specimens - the so-called holotypes and syntypes - from four similar species from the natural history museums in Copenhagen, Stockholm and Oxford, as well as the German Entomological Institute, to study the differences closely . "Together with the hoverflies expert Dieter Doczkal from Malsch Dziock described the new kind.

Relic in primeval oak and beech trees

Dziock found two males in the biosphere reserve Flusslandschaft Elbe near Dessau (Saxony-Anhalt), a female in the Hainich National Park (Th ringen). Other entomologists have now been able to prove this hover fly in Hesse and Rhineland-Palatinate. "It is no coincidence that we have found this species in protected locations, " says Dziock, referring to the sites, the jungle-like oak and beech trees.

"Newer" forests that have not been wooded for so long do not harbor such relic species. Since these species are not as adaptable and less mobile as other species, today they are only very island-like in the remnants of primeval, ancient forests. Because typical old wood structures such as tree hollows, slime flows or modern heartwood only emerge after at least 120 years. However, most trees in managed forests are already filled before reaching this age.

Modern forestry as a problem for biodiversity

"Where conventional forestry is practiced, this species has no chance of survival. Everything that looks sick is removed. But it is just such old trees that form the mucus flows that these species need. "From the point of view of biologists, it is therefore necessary to leave old trees in the forests and let them die there in a natural way.

The forest guideline of Saxony-Anhalt sees Dziock critically, as it leaves too much discretion in the economic utilization and on top of that, the forest owners are not even bound by this guideline. "It is not enough to leave some dead wood in the forest, " he explains. "After a short time, this wood is so dry that it no longer offers any habitat to the larvae of hoverflies. Deadwood is not a substitute for naturally occurring waste wood. "

Forests with an age of more than 180 years account for only about two percent in Germany. This has serious consequences for biodiversity. Evaluations of the list of endangered species show that especially those species of animals or plants that are specialized in typical structures of semi-natural forests are disproportionately at risk.

(idw - Environmental Research Center Leipzig-Halle, 31.03.2005 - DLO)