Insights on various treatment typologies

Chemical control methods:

LLINs:

Long-Lasting Insecticide-Treated Nets (LLINs) represent a relatively new approach in the context of Integrated Pest Management (IPM) for the control of P. japonica. These nets, with fibres impregnated or coated with pyrethroids, are assembled in attract-and-kill devices, to lure and kill adult P. japonica. The insects are attracted by a dual semiochemical lure placed near the nets, they walk on the LLINs for approximately 90 seconds and then become paralyzed and eventually die within minutes. (Marianelli et al., 2019). Both lab and field tests have demonstrated their efficacy in killing beetles and reducing local population density with minimal environmental impact (Paoli et al., 2023). Recent studies indicate that using a single net per hectare may represent a good trade-off between effectiveness and management efforts to lower adult populations in infested areas (Paoli et al., 2024).

Agronomical and Physical practices

Crop rotation:

Grubs do not pose a threat to alsike clover (Trifolium hybridum L.), red clover (T. pratense L.), white clover (T. repens L.), alfalfa (Medicago sativa L.), soybean (Glycine max (L.) Merr.), buckwheat (Fagopyrum esculentum Moench), oats (Avena sativa L.), barley (Hordeum vulgäre L.), common rye (Sécale céréale L.), or orchardgrass (Dactylis glomerata L.). Implementing these crops in rotation helps reducing insect damage (Fleming, 1976).

Tillage:

Cultivating the soil to a depth of 8 cm in summer brings the eggs to the surface, where they are killed by sun and wind. This method destroys about 25 to 30 percent of the eggs. Furthermore, plowing to about 15 cm, followed by disking and harrowing to 8 cm destroyed 40 to 50 percent of the grubs in fallow fields and 25 to 30 percent in sodland. However, in pastures a lower mortality rate occurred due to the breakup of the clods of not always occurred. Instead, using implements that pulverize the soil and prepare the land for planting in one operation proved more effective in killing grubs than the common farm implements; these include "Rototillers" and "Rotocultivators":

One pulverization on fallow or sodland killed about 70 percent of the grubs

• Two about 82%
• Three about 94%

The best results were obtained when the grubs were close to the soil surface, specifically in early fall and late spring (Fleming, 1976).

Kaolin:

Caution is advised because kaolin is washed off by rain. If this treatment is not repeated over time, it will not protect newly developing shoots (Bosio, technical communication).

Biological control methods:

EPN (Entomopathogenic Nematodes):

These organisms have a unique mechanism to kill their hosts: the infective juveniles (Ijs), the only free-living stage of EPN, move in the soil seeking P. japonica larvae. Upon encountering their hosts, the IJs penetrate the larvae through the natural body openings (mouth, anus, and spiracles) or through thin areas of the cuticle. Once inside the larval body, the IJs release symbiotic bacteria, which multiply rapidly, producing toxins and exoenzymes that compromise the insect's immune system, leading to death by septicemia.

Finally, a new group of IJs goes out into the soil and searches for new hosts (Poinar, 1990). The control of P. japonica larvae is more effective when the natural strains of Heterorhabditis bacteriophora are applied against first and second instars larvae (Power et al., 2009; Koppenhöfer and Fuzy, 2004; Marianelli et al., 2018; Torrini et al., 2020). In the case of application against third instars, pre-wintering larvae are more susceptible than post-wintering ones (Paoli et al., 2017). Furthermore, EPN natural strains possess physiological traits well-adapted to local ecological conditions. As a result, they thrive in their native soils and can persist there for years, thereby reducing the need for additional treatments (Gotta et al., 2023).

EPF (Entomopathogenic Fungi):

Entomopathogenic Fungi (EPF), such as Metarhizium spp. and Beauveria spp., act as biological control agents by infecting and killing insects through their cuticle. These fungi grow inside the host until it dies. They are used for the control of P. japonica at both larval and adult stages. EPF treatments are generally applied as conidia or blastospores in the soils. Studies have shown variable results: for instance, Metarhizium brunneum was effective against P. japonica adults but less against larvae (Barzanti et al., 2023; Graf et al., 2023). Furthermore, the use of native strains such as Metarhizium robertsii for the control of larvae has been tested in some fields reporting moderate results (Marianelli et al., 2024).

Predators/parasitoids:

Natural enemies have been identified from the Japanese beetle’s native range (Potter & Held 2002). For its management, at least 47 species of predatory and parasitic insects from Asia and two from Australia were released in the United States (Althoff & Rice, 2022). Out of these, Tiphia vernalis (Fig. 1S3) Rohwer (Hymenoptera: Tiphiidae), proved to be the most effective in reducing P. japonica population densities (Potter & Held 2002).

The female of T. vernalis paralyses the larvae by stinging the host in the ventral nerve cord and oviposits the eggs between the third thoracic and the first abdominal segment (Balock, 1934; Rogers & Potter, 2003). When the larvae emerge as adults, honeydew and floral nectar serve as important food sources for the primary diet of T. vernalis.

For Tiphia vernalis in a stand of turf, the parasitism rate is higher if plants of Paeonia lactiflora are introduced in the target environment (Rogers & Potter, 2004). Also, black cherry (Prunus serotina Ehrh. c.) provides another nectar source that benefits this insect; the presence of nearby nectar sources influences the T. vernalis effectiveness and determines a high parasitization rate. Then, black cherry is another tool to increase the biological control of P. japonica in landscape management (Mclaughin et al., 2022).

Tiphia popilliavora:

Tiphia popilliavora wasp female lays eggs on the first or second thorax segments (Althoff & Rice, 2022); then T. popilliavora larvae feed externally on the host (Balock et al., 1934). Similarly, for T. popilliavora it is recommended to plant peonies or wild parsnip, because they promote the establishment and spread of wasp populations, increasing parasitism rates (Althoff & Rice, 2022).

Istocheta aldrichi:

it is a tachinid fly that parasitizes P. japonica adults. Its eggs are laid on the adult’s prothorax. Then, I. aldrichi larvae move into the internal organs, after their first molt. After the oviposition, P. japonica survives for 5-9 days. However, if spring temperatures are high, early fly emergence will occur, misaligning the adult phenology of the host (Althoff & Rice, 2022).

Saponins:

Saponins extracted from alfalfa (Medicago sativa) are biologically active molecules that have demonstrated anti-feedant and insecticidal effects against P. japonica. They act as a food deterrent causing a significant reduction in the consumption of treated leaves compared to untreated ones. Furthermore, at a concentration of 3% saponins have been observed to increase mortality in P. japonica adults (Iovinella et al., 2023).

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