Abstract
Bursaphelenchus xylophilus (Steiner & Buhrer) Nickle, is a serious forest pest, causing enormous economic losses in pine trees in Korea, China, Japan, and countries in Western Europe. To prevent pine wilt disease (PWD), trunk injection with nematicide is performed in Korea. Although these nematicidal agents are quite efficient, the development of new nematicidal agents is needed to prevent pesticide resistance and reduce pest management costs. The aim of this study was to investigate nematicidal activities of pure naphthoquinones (NTQs)–1,4-NTQ, juglone, and plumbagin—against B. xylophilus via in vitro and semi-in vivo assays to identify new candidate agents for trunk injection. Estimated LC50 values (48 h exposure) were 100.0 ppm, 57.0 ppm, and 104.0 ppm for 1,4-NTQ, juglone, and plumbagin, respectively. In the semi-in vivo assay on pine bolt of the Japanese black pine, Pinus thunbergii, the population of inoculated B. xylophilus was significantly decreased at two weeks after treatment with juglone when compared with the effects of treatment with 1,4-NTQ and plumbagin. We also observed that naphthoquinones could generate reactive oxygen species, which presumably indicated that naphthoquinones caused significant oxidative stress in B. xylophilus. The findings of this study suggest the nematicidal potential of naphthoquinones and their possible use in further in vivo assays to test their nematicidal efficacy against B. xylophilus when injected through trunk injection.
Highlights
The pine wilt disease (PWD) caused by the pinewood nematode, Bursaphelenchus xylophilus (Steiner & Buhrer) Nickle, results in huge economic losses in coniferous species, especially pines, throughout East Asian countries, including Japan, South Korea, and China [1], as well as in WesternEurope [2]
The findings of this study suggest the nematicidal potential of naphthoquinones and their possible use in further in vivo assays to test their nematicidal efficacy against B. xylophilus when injected through trunk injection
Trunk injection with systemic nematicides is an effective way to manage PWD by directly killing B. xylophilus, which is the source of PWD, and is a more environmentally stable strategy of pest control; this strategy is widely used in South
Summary
The pine wilt disease (PWD) caused by the pinewood nematode, Bursaphelenchus xylophilus (Steiner & Buhrer) Nickle, results in huge economic losses in coniferous species, especially pines, throughout East Asian countries, including Japan, South Korea, and China [1], as well as in WesternEurope [2]. In South Korea, PWD was first reported in Busan in 1988 [3], and after several decades, it eventually spread to most parts of the country. Several studies using plant essential oils and herbal extracts have been conducted to search for novel nematicides that negatively affect the propagation of B. xylophilus [5,6,7]. Despite these efforts, no nematicides for trunk injection against B. xylophilus have been developed as they have significantly lower efficacy than do conventional nematicides, such as avermectin and emamectin benzoate, for preventing PWD in vivo [8]
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