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Popillia japonica: get ready for this new pest

There is an immediate threat for the Italian crop and plants and it comes from Japan. It's called Popillia japonica or, commonly, Japanese beetle. After a recent attack observed in Lombardy and clearly attributable to this species, the alarm is rightly high. Extremely polyphagous, this coleopter can attack almost 300 species of plants, whether herbaceous or woody. Several host plants are valuable crops such as vines, various species of flowers and ornamental plants.
In Japan, where is native, is not responsible for infestations due to the presence of some antagonists. Arrived in the US in 1916, it has spread rapidly and in 1967 it was present in 23 states. The lack of enemies, the favorable climate and the high range of guests are the factors that determined such a rapid spread. Being difficult to eradicate, it seems that the only way to manage it is to control its diffusion. Listed as A1 Eppo among quarantine insects, it was firstly reported in the European continent in Portugal and Russia.
Description. The adults are up to 1 cm in length and about 7 mm in width. They have a characteristic metallic bright green color with copper-colored wing covers. Laterally it has gray hairs left uncovered on the abdomen. The most important identifying trait for this species is these five spots of hairs on each side. Males are slightly smaller than females; the antennas are generally hidden in both sexes and become visible only when the insect perceives odorous stimuli or pheromones.
The eggs have a diameter of about 1.5 mm with colors varying from white to cream; during the development they increase in volume until doubling.
The larvae are transparent, yellowish-white and covered with brown hairs and spines. 10 abdominal segments and 3 thoracic can be distinguished. Each one of these brings a pair of legs. The accumulation of feces in proctodeum (posterior intestine) gives a dark color to the end of the insect. During the rest period the larva is found in the soil in the characteristic shape of a C, typical of Scarabaeidae. After the last larval stage the insect pupate in cells in the soil presenting colors ranging from yellow to metal green in relation to the age.
Biology. Generally the life cycle of Japanese beetle is 1 year, 2 in particularly cold climates. The variables that regulate the development of the insect are essentially latitude and altitude. The adults appear in May and June but in the northernmost areas this can be delayed until the beginning of July. Immediately after, the breeding season begins, with the emission of pheromones by the virgins that stimulate males. These, coming in large numbers to form groups called “balls”, they become very competitive. The oviposition occurs preferentially on grass species, which are the most preferres for the nutrition of the future larvae. The factor that determines the choice of the site seems to be the softness of soil and the degree moisture.
The female digs into the ground and lay up to 3 eggs and then re-emerge to feed and mate again. During the season each female can make this process for many times to lay up to 60 eggs in total. Hatching occurs about two weeks after oviposition and the larvae feed on young roots for two months. The activity is interrupted in autumn when the temperature drops around 10°C. The following spring, the larvae take up the trophic activity and after about a month they become pupae. After a period ranging from 1 to 3 weeks the metamorphosis takes place in adult stage that lasts an average of a little over a month with substantial differences between populations living in different climates. The lifespan of the adults tends to be longer in colder temperatures and shorter with warmer temperatures.
Devastating damages. P. japonica in the larval stage is able to destroy entire plots of grass and cultivated fields. The aggression is recognized by the arrival of dried patches on the surface of lawns. It’s however necessary to take samples to detect the actual presence of the pest in the soil. Generally, when the presence of larvae is higher than the average of 90/m2 a treatment is needed. The adult mainly feeds on woody species eating the leaves. The bites affect the entire leaf surface but not the ribs, giving the leaves a characteristic skeletal appearance. The adults are capable of producing effective aggregation pheromones, so that also the presence of a few individuals can represent a serious threat. They respond very well to the emission of volatile compounds by attacked plants, that also attract other species of beetles.

Manual removal is the best method in cases of limited infestation. Some traps that are useful for monitoring have been also tested, but they are ineffective in case of massive captures.
Beetles and ants predators of this pest have been found but their introduction should be evaluated very well since problems derived from specificity might emerge.
Two wasps from Asia, Tiphia vernalis and Tiphia popilliavora, have proved to be effective as parasitoids of P. japonica. The nematode Steinernema kushidai has been shown to cause mortality similar to that of organophosphate insecticides.
Bacillus thuringiensis, by producing poisonous toxins once ingested, is a bacterium that could be very effective in combating this dangerous pest that threatens our country.

The beetle, observed in Lombardia, is able to attack almost three hundred species of plants. Read about the problems related to control and to the rapid spread of this pest