After the first confirmed discovery of a Japanese beetle In Bavaria at the beginning of August on the A 96 near Lindau, two more beetles were discovered in special traps set up by the State Office for Agriculture (LfL): one also near Lindau, the other on the A 93 near Kiefersfelden. The LfL has stepped up its controls in both regions. The Japanese beetle is an inconspicuous but very voracious insect from the Far East that can cause great damage to agriculture, but also to parks and sports facilities. Before it appeared in Bavaria, it had already appeared in Switzerland and Baden-Württemberg this summer. The insect was most likely brought to Europe by plane from the Far East.
However, experts currently assume that the three Japanese beetles discovered so far are so-called hitch-hikers. By this they mean individual animals that have traveled on trucks or in cars. The reason for this assumption is that the three locations are all near motorways that lead from northern Italy and Switzerland to Bavaria. In Baden-Württemberg, individual Japanese beetles have also been caught again and again since 2021, which obviously got there as hitch-hikers.
The experts at the LfL fear the Japanese beetle because its larvae feed on more than 400 host plants. Among them are many that play a major role in agriculture, such as grapevines and corn, but also soy and berries. Linden trees, birches and other landscape trees as well as roses, wisteria and similar ornamental plants are also affected by it. In northern Italy, the Japanese beetle, which is copper-brown and metallic green in color and can appear in large swarms, has reportedly already destroyed entire sports fields.
“The same basic principle applies to all invasive species,” says biologist Andreas Segerer, who works at the Zoological State Collection in Munich. “They have no natural enemies here; they encounter a biological system that is not prepared for them and therefore cannot control their spread.” Segerer is not a specialist in the Japanese beetle or other invasive species, but rather a butterfly expert. But as such, he also has to deal with invasive species again and again.
The Asian tiger mosquito and the Asian longhorned beetle are two further examples of immigrants that repeatedly cause a stir, at least regionally. The Asian tiger mosquito because it can basically transmit dangerous pathogens such as the dengue virus or the chikungunya virus. An infection with one of these can lead to severe fevers and sometimes even death. The Asian tiger mosquito is very rare in Germany. In Bavaria there is currently only one population in Fürth in Central Franconia. Furthermore, according to the AOK, no case has yet been documented in which an Asian tiger mosquito has infected a person with a dangerous disease in Germany. But it is generally expected that the species will spread further as a result of climate change. Asian tiger mosquitoes are tiny and have a striking black and white pattern. They came to Europe in the 1990s with travel and freight traffic.
The Asian longhorn beetle is native to China and Korea and attacks birch, willow, horse chestnut and other deciduous trees. The females lay their eggs in them, and the larvae eat their way through the trunk until the host tree dies. The 2.5 to 4 centimetre-long animals have striking black and white ringed antennae that are twice as long as their bodies. The longhorn beetle travels the world in the wood of transport pallets. It first appeared in Bavaria 20 years ago – near Passau in Neukirchen am Inn. In Feldkirchen near Munich, parks and small forests were felled from 2012 onwards to stop it. The pest has also been detected near Augsburg, in Kelheim, near Murnau and in Miesbach. However, following massive control measures, most of the populations are considered to be extinct. Precautionary measures are in place in the Miesbach region until the end of the year.
But there are also examples of invasive immigrants losing their potential for damage over time or at least significantly reducing it. One is the Horse chestnut leaf minerwhich spread from the Balkans to Austria in the 1990s and then appeared in Bavaria shortly afterwards. The larvae of this small butterfly eat their way into the leaves of the chestnuts in large numbers, causing them to turn brown prematurely and wilt. This severely weakens the trees. Some experts feared at the time that this could lead to a mass death of horse chestnuts. “But that has not happened,” says butterfly expert Segerer. One important reason in his view: “parasitic wasps and even birds such as blue tits soon discovered that they can eat the caterpillars. The blue tits even peck really hard into the chestnut leaves so that they can get to the caterpillars.” In any case, no one is talking about the death of horse chestnuts anymore.