Invasion of Popillia japonica in Lombardy, Italy: Interactions with soil entomopathogenic nematodes and native grubs

Abstract

1. The recent invasion of the Japanese beetle Popillia japonica Newman (Coleoptera: Scarabaeidae) in northern Italy offered the opportunity to explore the entomopathogenic nematodes (EPNs) associated with the soil of hay meadows. 2. A total of 61 sites were considered for nematode sampling, and from 17 of them (27.9%) EPNs were isolated and further characterized with molecular and morphological techniques as well as with laboratory bioassays. 3. Two main species, Heterorhabditis bacteriophora Poinar (Rhabditida: Heterorhabditidae) and Steinernema carpocapsae Weiser (Rhabditida: Steinernematidae) were recorded with the same frequency together with a few other species (Rhabditida: Oscheius sp. and Phasmarhabditis sp.).4. The newly isolated EPN populations were characterized for their activity (penetration rate) and infectivity to P. japonica grubs. 5. EPNs occurrence was related to the time of beetle invasion at each sampling site and there was evidence of a density-dependent response of the EPNs community to P. japonica density.6. The invasion of P. japonica apparently did not significantly affect the occurrence of native grubs, although a tendency to a decline was observed and should be further investigated.

Biocontrol potential of six Heterorhabditis bacteriophora strains isolated in the Azores Archipelago

“…These isolates have the potential to become biological control agents for P. japonica as EPNs isolated from areas already infested are proposed to exhibit heightened virulence against the pest (Lacey et al 2015; Glazer et al 2022). Besides, these strains could display superior adaptability to the environmental and soil conditions for field applications.…”

“…The Japanese beetle, Popillia japonica (Coleoptera: Scarabaeidae), stands as a major insect pest native to Japan that reached mainland Europe in 2014 causing great damage in the Italian region (Glazer et al 2022; Gotta et al 2023). The larval stage exerts detrimental effects on grasslands and pastures, whereas adults feed on the foliage of agricultural crops and ornamental plants (Potter and Held 2002).…”

Popillia japonica – Italian outbreak management

“…This work, together with the restriction that only native EPN species can be field-released in Italy (EU Habitats Directive, art. 12, DPR 120/2003), has encouraged the search for local and better adapted EPN strains, especially in the two regions mostly infested by P. japonica : Piedmont ( 90 ) and Lombardy regions ( 91 ). Torrini et al.…”

“…Since native EPN isolates possess physiological traits that are adapted to local ecological conditions, the idea of supporting the ecosystem by propagating EPNs that thrive in their native soil could be considered as a basis for an eco-friendly approach to control this pest. In addition, a density-dependent response of EPNs to P. japonica has been shown since its introduction, indicating the great potential of these organisms as natural regulators of P. japonica populations ( 91 ). However, a decline in native scarab beetle populations has also been observed, indicating the generalist nature of soil EPNs ( 91 ).…”

“…In addition, a density-dependent response of EPNs to P. japonica has been shown since its introduction, indicating the great potential of these organisms as natural regulators of P. japonica populations ( 91 ). However, a decline in native scarab beetle populations has also been observed, indicating the generalist nature of soil EPNs ( 91 ). In addition to classic EPNs, other parasitic nematodes of P. japonica have been reported in Italy, such as the new species Hexamermis popilliae Poinar, 2017 (Nematoda: Mermithidae) ( 92 ) ( Figures 7A, B ) and Oscheius myriophilus (Poinar, 1986) (Nematoda: Rhabditidae) ( 93 ), both isolated from P. japonica .…”