Summer, sun, mosquitoes – weather favorable for the brood

Whirring, itching, scratching: mosquitoes seem to be particularly active and aggressive in this early summer. Is that correct? Doreen Werner, biologist at the Leibniz Center for Agricultural Landscape Research (ZALF) in Müncheberg, Brandenburg, can reassure you. “We have no mosquito plague,” she assures.

The feeling of being swarmed around by a particularly large number of pests outdoors is more due to the memory of the two dry and warm previous years. They were less favorable for the increase in bloodsuckers. The rainy weeks in April and May have given the insects wings. “Basically we have a completely normal mosquito year now,” explains Werner.

The scientist specializes in researching around 50 known mosquito species in Germany. This year the house mosquito as well as the forest and meadow mosquito had a good time due to the rainy months, she reports. The brood thrived in artificial reservoirs such as rain barrels as well as in puddles and stagnant natural waters. For the house mosquito, the sudden and sustained warmth is now particularly beneficial for reproduction: it often only takes a week from the blood-sucking females to lay their eggs until they hatch. At the moment the second generation is buzzing, others would follow. Forest and meadow mosquitoes, on the other hand, often only lived up to the beginning of August at the latest.

“In addition, the flood in some places also caused the flood mosquitoes,” said Werner. “Due to all three factors combined, some regions now have an increased number of mosquitoes.” Plage would have been said too much there too.

Werner and her team launched the “Mosquito Atlas” for their research around ten years ago. Interested parties can send in well-preserved specimens and have them determined. At the research center in Müncheberg, maps are created showing which species are widespread in which regions of Germany. So far there have been around 58,000 entries.

With climate change, a new point comes into focus: Are tropical species such as the Asian tiger mosquito introduced? And to what extent are there pathogens like the West Nile virus from hotter regions of the world in house mosquitoes in Germany?

The Robert Koch Institute (RKI) assumes that the West Nile virus will also circulate between mosquitoes and birds this summer. To a lesser extent, mosquito-borne infections in humans and horses are to be expected, especially in July and August, according to the latest epidemiological bulletin. So far, there have been few registered cases in humans in 2019 and 2020. Those affected lived in Berlin, Saxony-Anhalt and Saxony. The RKI considers an expansion of the affected regions to be possible. Because the virus can overwinter in mosquitoes. “Temperatures above 20 degrees are great for these viruses to multiply,” adds Werner. Some patients then experience flu-like symptoms. Serious courses are rare, but can be fatal.

The pandemic with its travel restrictions meant that fewer mosquito species “felt” were introduced from abroad, says the researcher. The Asian tiger mosquito, for which there is already evidence in Germany, has probably not spread further after the submissions for the mosquito atlas. So far, sites in Munich, Fürth, Frankfurt (Main), Heidelberg, Freiburg, the Upper Rhine Graben and in Jena are known. Tiger mosquitoes are striped white. They circle their victims in swarms, pursue them penetratively and attack again after a few seconds even when they are scared away. They can transmit tropical pathogens such as Zika, Chikungunya and Dengue viruses. In Germany, however, this is still unlikely because the viruses – apart from Chikungunya – can only multiply well in mosquitoes at high temperatures.

© dpa-infocom, dpa: 210614-99-982513 / 2

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