Introduction
In Germany, there have been only isolated findings of the Japanese beetle so far, but in Italy and Switzerland it is already causing significant damage. Which crops does it infest and how can it be controlled?
Authors
Our authors: Dr. Stephanie Feltgen, Dr. Björn Hoppe, and Dr. Matthias Becker, Julius Kühn Institute
Impact on Crops
The Japanese beetle poses a significant threat to almost all agricultural and horticultural crops because it feeds on a wide variety of plants. Over 400 species have recently been listed as primary and secondary hosts. The European Union has therefore classified the Japanese beetle as a so-called priority quarantine pest, making it reportable.
Damaging Effects
The Japanese beetle, belonging to the scarab beetle family (Popillia japonica), infests herbaceous and woody plants, as well as monocotyledonous and dicotyledonous wild and cultivated plants alike. Among the most important domestic arable crops such as cereals, maize, potatoes, sugar beets, legumes, and oilseeds, there is not a single one that it spares.
Preferred Hosts
Sweet grasses are primary hosts for the Japanese beetle. Cereals and maize are among the main hosts, with the beetle preferring them for egg laying. In grasslands, it favors ryegrass, fescue, and bentgrass.
Infestation of Various Plants
The Japanese beetle has been observed as a pest on many vegetable plants such as asparagus, carrots, pumpkins, and garden beans. Cabbage varieties, as well as chard and beets, are also among its secondary hosts. Vegetables grown in greenhouses or polytunnels (e.g., tomatoes, eggplants, cucumbers, melons) are also affected, but are better protected from incoming beetles due to covering.
Impact on Orchards and Vineyards
Almost all fruit trees are primary hosts of the Japanese beetle, including strawberries, currants, gooseberries, blackberries, blueberries, sloes, and almost all pome fruits (apple, pear, quince) and stone fruits (sweet cherry, sour cherry, plum, mirabelle, apricot, and peach). Grapes and hops are also major hosts of the Japanese beetle.
Resistance to Natural Defenses
The Japanese beetle appears to tolerate a variety of well-known defense compounds. The mustard oils of crucifers affect it as little as the ingredients of ivy and geraniums. It even shows no aversion to some conifers and ferns.
Life Cycle
The Japanese beetle lays its eggs in the soil. If grasslands and lawns are absent, it will use other plants for egg laying. While the larvae feed on plant roots and dead organic matter, the beetles emerging in spring feed exclusively on above-ground plant parts. They prefer softer material such as leaves and flowers, but also feed on various fruits.
Introduction to Europe
Originally from Japan, the beetle was introduced to North America in the early 20th century. It became a serious pest in the USA, particularly on lawns and in apple cultivation. In 2014, the Japanese beetle was detected on the European mainland in Italy. The beetles were likely introduced via Milan airport. Despite extensive control measures, its establishment in Northern Italy could not be prevented.
