Nematicidal Activities of Saccharin and Erythritol Against Pinewood Nematode.

The pinewood nematode (PWN), Bursaphelenchus xylophilus (Steiner & Bührer), causes pine wilt disease (PWD) resulting in severe environmental damage to pine forest ecosystems worldwide. To develop alternative strategies for managing PWD, the nematicidal activities of two sweeteners, erythritol and saccharin, were investigated. Among these two sweeteners, saccharin induced higher mortality in a dose-dependent manner. The LC50 and LC90 values of saccharin were estimated to be 0.321 M and 0.615 M, respectively. However, erythritol did not exhibit nematicidal activities. The results of our study demonstrated that saccharin is lethal to PWN and shows nematicidal effects in a dose-dependent manner. Although the mechanisms of saccharin toxicity are not yet investigated, saccharin could be used as an effective alternative for the management of PWN.

Directed evolution of glycosyltransferase for enhanced efficiency of avermectin glucosylation.

Avermectin, produced by Streptomyces avermitilis, is an active compound protective against nematodes, insects, and mites. However, its potential usage is limited by its low aqueous solubility. The uridine diphosphate (UDP)-glycosyltransferase (BLC) from Bacillus licheniformis synthesizes avermectin glycosides with improved water solubility and in vitro antinematodal activity. However, enzymatic glycosylation of avermectin by BLC is limited due to the low conversion rate of this reaction. Thus, improving BLC enzyme activity is necessary for mass production of avermectin glycosides for field application. In this study, the catalytic activity of BLC toward avermectin was enhanced via directed evolution. Three mutants from the BLC mutant library (R57H, V227A, and D252V) had specific glucosylation activity for avermectin 2.0-, 1.8-, and 1.5-fold higher, respectively, than wild-type BLC. Generation of combined mutations via site-directed mutagenesis led to even further enhancement of activity. The triple mutant, R57H/V227A/D252V, had the highest activity, 2.8-fold higher than that of wild-type BLC. The catalytic efficiencies (Kcat/Km) of the best mutant (R57H/V227A/D252V) toward the substrates avermectin and UDP-glucose were improved by 2.71- and 2.29-fold, respectively, compared to those of wild-type BLC. Structural modeling analysis revealed that the free energy of the mutants was - 1.1 to - 7.1 kcal/mol lower than that of wild-type BLC, which was correlated with their improved activity. KEY POINTS: • Directed evolution improved the glucosylation activity of BLC toward avermectin. • Combinatorial site-directed mutagenesis led to further enhanced activity. • The mutants exhibited lower free energy values than wild-type BLC.

Intraocular lens power calculation using adjusted corneal power in eyes with prior myopic laser vision correction.

PURPOSE: To evaluate the prediction accuracy of the intraocular lens (IOL) power calculation using adjusted corneal power according to the posterior/anterior corneal curvature radii ratio in the Haigis formula (Haigis-E) in patients with a history of prior myopic laser vision correction. METHODS: Seventy eyes from 70 cataract patients who underwent cataract surgery and had a history of myopic laser vision correction were enrolled. The adjusted corneal power obtained with conventional keratometry (K) was calculated using the posterior/anterior corneal curvature radii ratio measured by a single Scheimpflug camera. In eyes longer than 25.0 mm, half of the Wang-Koch (WK) adjustment was applied. The median absolute error (MedAE) and the percentage of eyes that achieved a postoperative refractive prediction error within ± 0.50 diopters (D) based on the Haigis-E method was compared with those in the Shammas, Haigis-L, and Barrett True-K no-history methods. RESULTS: The MedAE predicted using the Haigis-E (0.33 D) was significantly smaller than that obtained using the Shammas (0.44 D), Haigis-L (0.43 D), and Barrett True-K (0.44 D) methods (P < 0.001, P = 0.001, and P = 0.014, respectively). The percentage of eyes within ± 0.50 D of refractive prediction error using the Haigis-E (78.6%) was significantly greater than that produced using the Shammas (57.1%), Haigis-L (58.6%), and Barrett True-K (61.4%) methods (P = 0.025). CONCLUSION: IOL power calculation using the adjusted corneal power according to the posterior/anterior corneal curvature radii ratio and modified WK adjustment in the Haigis formula could improve the refraction prediction accuracy after cataract surgery in eyes with prior myopic laser vision correction.

Nematicidal Activities of Three Naphthoquinones against the Pine Wood Nematode, Bursaphelenchus xylophilus.

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.

Cholinesterase inhibitory alkaloids from the rhizomes of Coptis chinensis.

Coptis chinensis has been used as a medicinal herb in traditional oriental medicine. In this study, chemical investigation of a water extract of C. chinensis identified two new quaternary protoberberines (1, 2), a new tricyclic amide (3), together with five known compounds. Their chemical structures were elucidated by analysis with 1D and 2D NMR and high-resolution mass spectroscopy, as well as by comparison with those reported in the literature. Compounds 4, 5, and 7 showed potent inhibition against acetylcholinesterase (AChE) with IC50 values of 1.1, 5.6, and 12.9 µM, respectively. Compounds 2 and 4 showed inhibition of butyrylcholinesterase (BChE) with IC50 values of 11.5 and 27.8 µM, respectively. The kinetic activities were investigated to find out the type of enzyme inhibition involved. The types of AChE inhibition shown by compounds 5 and 7 were noncompetitive; BChE inhibition by compound 2 was also noncompetitive.

Myrtaceae Plant Essential Oils and their ß-Triketone Components as Insecticides against Drosophila suzukii.

Spotted wing drosophila (SWD, Drosophila suzukii (Matsumura), Diptera: Drosophilidae) is recognized as an economically important pest in North America and Europe as well as in Asia. Assessments were made for fumigant and contact toxicities of six Myrtaceae plant essential oils (EOs) and their components to find new alternative types of insecticides active against SWD. Among the EOs tested, Leptospermum citratum EO, consisting mainly of geranial and neral, exhibited effective fumigant activity. Median lethal dose (LD50; mg/L) values of L. citratum were 2.39 and 3.24 for males and females, respectively. All tested EOs except Kunzea ambigua EO exhibited effective contact toxicity. LD50 (µg/fly) values for contact toxicity of manuka and kanuka were 0.60 and 0.71, respectively, for males and 1.10 and 1.23, respectively, for females. The LD50 values of the other 3 EOs-L. citratum, allspice and clove bud were 2.11-3.31 and 3.53-5.22 for males and females, respectively. The non-polar fraction of manuka and kanuka did not show significant contact toxicity, whereas the polar and triketone fractions, composed of flavesone, isoleptospermone and leptospermone, exhibited efficient activity with the LD50 values of 0.13-0.37 and 0.22-0.57 µg/fly for males and females, respectively. Our results indicate that Myrtaceae plant EOs and their triketone components can be used as alternatives to conventional insecticides.

Fumigant and contact toxicity of 22 wooden essential oils and their major components against Drosophila suzukii (Diptera: Drosophilidae).

Fumigant and contact toxicities of 22 plant essential oils (EOs) from 14 families and their constituents against the adult spotted wing drosophila (SWD), Drosophila suzukii were examined. Analyses by GC, GC-MS, and NMR led to the identification of 2, 16, 13, 4, 6, 9, and 10 compounds from Gaultheria fragrantissima, Croton anistatum, Illicium verum, Liquidamabar orientalis, Cinnamomum cassia, Rosa damasena, and Santalum album, respectively. In fumigant toxicity test, G. fragrantissima, C. anistatum, and I. verum exhibited 100, 93.8, and 95.8, and 100, 70.0, and 80.0% mortalities against the adult male and female SWD at 4.41mg/L air, respectively. LC50 values (mg/L air) of G. fragrantissima, C. anistatum, and I. verum were 3.46, 3.67, and 3.16 against male, and 3.48, 4.31, and 4.01 against female SWD. LC50 values (mg/L air) of methyl salicylate and trans-anethole were 2.17 and 1.75 against male and 2.65 and 3.00 against female SWD, respectively. In contact toxicity tests, L. orientalis, C. cassia, R. damasena, and S. album showed insecticidal activity with LD50 values (µg/fly) of 2.64, 1.84, 3.40 and 2.18 against male SWD and of 3.74, 2.24, 8.91 and 5.61 against female SWD, respectively. 2-Phehy-1-ethanol, 3-phenyl-1-propanol, trans-cinnamaldehyde, trans-cinnamyl alcohol, and α-santalol also exhibited insecticidal activity with LD50 values of 9.79, 5.52, 2.39, 3.02 and 2.37 against male SWD and of 11.77, 7.04, 2.94, 3.32, and 3.99 against female SWD, respectively. trans-Cinnamaldehyde exhibited the highest AChE inhibition but its inhibition is likely due to a non-specific chemical inhibition. Our results indicate that wooden EOs and their components can be used as fumigants or spray-type control agents against SWD.

Identification of the female-produced sex pheromone of the plant bug Apolygus spinolae.

Apolygus spinolae (Meyer-Dür) (Heteroptera: Miridae) is an important pest of fruit and tea trees in Korea and Japan. Analyses of extracts of metathoracic scent glands revealed that those of female bugs contained hexyl butyrate, (E)-2-hexenyl butyrate, and (E)-4-oxo-2-hexenal in a ratio of 20:100:7. The glands of males contained the same three compounds, but the ratio of the components was quite different, with hexyl butyrate being the most abundant. Field trapping tests with various blends of the synthetic compounds dispensed from high-density polyethylene tubes showed that (E)-2-hexenyl butyrate and (E)-4-oxo-2-hexenal were essential for attraction of male A. spinolae, and catches with a wide range of ratios of these two compounds did not differ significantly. However, adding hexyl butyrate at 50 % or more of the (E)-2-hexenyl butyrate to the binary blend strongly inhibited attraction of males. Trap catches increased with increasing amounts of a 10:1 blend of (E)-2-hexenyl butyrate and (E)-4-oxo-2-hexenal from 0.011 to 11 mg loaded into the tube. Catches of males in traps baited with lures containing 1.1 mg of the binary blend were not significantly different from catches in traps baited with live virgin females.

Fumigant toxicity and acetylcholinesterase inhibitory activity of 4 Asteraceae plant essential oils and their constituents against Japanese termite (Reticulitermes speratus Kolbe).

This study investigated the fumigant toxicity of 4 Asteraceae plant essential oils and their constituents against the Japanese termite Reticulitermes speratus Kolbe. Fumigant toxicity varied with plant essential oils or constituents, exposure time, and concentration. Among the tested essential oils, those from Chamaemelum nobile exhibited the strongest fumigant toxicity, followed by those from Santolina chamaecyparissus, Ormenis multicaulis, and Eriocephalus punctulatus at 2 days after treatment. In all, 15, 24, 19, and 9 compounds were identified in the essential oils from C. nobile, E. punctulatus, O. multicaulis, and S. chamaecyparissus, respectively, by using gas chromatography, gas chromatography-mass spectrometry, or open-column chromatography. The identified compounds were tested individually for their fumigant toxicity against Japanese termites. Among the test compounds, trans-pinocarveol, caryophyllene oxide, sabinene hydrate, and santolina alcohol showed strong fumigant toxicity against Japanese termites. Acetylcholinesterase (AChE) inhibition activity of the identified compounds from C. nobile, E. punctulatus, O. multicaulis, and S. chamaecyparissus essential oils were tested to determine the mode of their action. The IC50 values of (+)-α-pinene, (-)-limonene, (-)-α-pinene, ß-pinene, and ß-phellandrene against Japanese termite AChE were 0.03, 0.13, 0.41, 0.42, and 0.67mg/mL, respectively. Further studies are warranted to determine the potential of these essential oils and their constituents as fumigants for termite control.

Pesticide residues and risk assessment of trunk-injected pesticides in pine nut (Pinus koraiensis) seeds.

Pine nuts, the edible seeds of pines (Family: Pinaceae, Pinus spp.), are popular worldwide, particularly those from the Korean pine tree (Pinus koraiensis), which is economically significant and widely exported. The spread of pine wilt disease (PWD) caused by pinewood nematodes (PWNs) has necessitated the use of trunk injections of pesticides in Korea, raising concerns about pesticide residues in edible pine nuts. This study investigated the concentration of pesticide residues in pine nuts from trunk-injected trees and assessed their potential health risks to consumers. After Korean pine tree was trunk-injected with pesticide, the pine nuts were subsequently harvested and analyzed for pesticide residues using LC‒MS/MS. Short- and long-term risk assessments of trunk-injected pesticides in pine nuts were conducted. Abamectin and emamectin benzoate were not detected, while acetamiprid and sulfoxaflor were detected, but their levels were below the maximum residue limits (MRLs) set by Korea, the EU, and the US. The short-term and long-term risk assessments indicated negligible health risks for consumers from these residues. Despite the low risk, we recommend continued monitoring of pesticide residues in pine nuts intended for sale to ensure consumer safety.

Pheromone-Based Mating Disruption of Conogethes punctiferalis (Lepidoptera: Crambidae) in Chestnut Orchards.

Chestnuts (Castanea crenata Siebold and Zucc.) are one of the major agroforestry products in Korea, and Conogethes punctiferalis is a major pest of the chestnut fruit. Pheromone-based mating disruption (MD) has emerged as a promising eco-friendly approach to reduce population levels and ultimately mitigate fruit damage. Field trials were conducted over two years (2022-2023) in two commercial chestnut orchards in Central Korea that were infested with C. punctiferalis. Compared with the control treatment, the MD treatment effectively reduced the number of male C. punctiferalis captured in the MD treatment plots. Male catch inhibition (MCI) rates ranged from 70.5% to 82.7% in 2022 and from 87.8% to 95.1% in 2023. The MD efficacy (%) was calculated based on the total number of chestnut fruits collected and the number of fruits damaged by C. punctiferalis. In 2022, the MD efficacy of the single-dosage treatment (TS, 50 g/ha) was 63.9% in Orchard A and 73.6% in Orchard B. In 2023, the MD efficacies of the double-dosage treatment (TD, 100 g/ha) and the two-application treatment (TT, 50 g/ha in June and August) were 60.2% and 77.9% in Orchard A and 50.9% and 64.8% in Orchard B, respectively. This study confirms the efficacy of pheromone-based MD in reducing the C. punctiferalis numbers in chestnut orchards and damage to chestnut fruits.

Identification and Field Bioassay of Rusicada privata (Lepidoptera: Erebidae) Sex Pheromone.

Rusicada privata (Lepidoptera: Erebidae) is a major pest insect on Hibiscus syriacus L. (Malvaceae: Malvales), which is usually planted in urban landscapes. Insecticidal control of R. privata is not ideal for urban landscaping due to its harmful effects and risk to human health. Therefore, nonchemical and ecofriendly alternatives are needed. To identify the sex pheromone of R. privata, abdominal tip extracts of male and female R. privata were analyzed by gas chromatography-mass spectrometry. The abundance of 7-methylheptadecane (7Me-17Hy) in female R. privata abdominal tip extracts led us to hypothesize that it is the major sex pheromone. The compound was tentatively identified by a mass spectral library and confirmed by matching retention times and mass spectra of the female-produced compound with those of a synthetic standard. The compounds elicited electroantennographic (EAG) activity. In a field trapping experiment, only synthetic lures containing 7Me-17Hy attracted R. privata males. The EAG activity and field trapping results confirmed that 7Me-17Hy is the sex pheromone of female R. privata. The results will aid in developing sex pheromone-based R. privata control techniques, such as mating disruption.

Effect of electron beam irradiation on the pine wood nematode, Bursaphelenchus xylophilus.

PURPOSE: Reproduction inhibition of the pine wood nematode (PWN) by electron beam (e-beam) irradiation both in vitro and in vivo was tested to determine if ionizing radiation could control the PWN by reducing survival and preventing reproduction, thus reducing the risk of pine wilt disease (PWD) spread. MATERIALS AND METHODS: E-beam (10 MeV) irradiation treatment at different doses (0-4 kGy) was applied to PWNs in a Petri dish. Treatment of pine wood logs infested with PWNs was performed at 10 kGy. Mortality was determined by comparing the survival rates before and after irradiation treatment. DNA damage by e-beam irradiation (0-10 kGy) in the PWN was determined using the comet assay. RESULTS: E-beam irradiation increased mortality and suppressed reproduction with increasing doses. The lethal dose (LD) values (kGy) were estimated as follows: LD50 = 2.32, LD90 = 5.03, and LD99 = 9.48. E-beam irradiation of pine wood logs significantly suppressed PWN reproduction. Comets of e-beam-irradiated cells showed an increased tail DNA level and moment with an increasing dose. CONCLUSION: This study suggests that e-beam irradiation could be used as an alternative method for the management of pine wood logs infested with PWNs.

Post-fumigation sub-lethal activities of phosphine and ethyl formate on survivorship, fertility and female sex pheromone production of Callosobruchus chinensis (L.).

Phosphine (PH3) and ethyl formate (EF), the two popular fumigant disinfectants of stored product insect pests, are primarily evaluated for their knock down effects without considering their post-fumigation sub-lethal activities. The sub-lethal activities (adult survivorship, fecundity, sterility and female sex pheromone production) of the fumigants were evaluated on a field-to-storage insect pest adzuki bean beetle, Callosobruchus chinensis (L.). The adults' survivorship and female fecundity, both were dose-dependently affected by sub-lethal PH3 and EF fumigation exposures. Hatchability of the eggs laid by fumigated female adults were also significantly affected. Gas-chromatography mass-spectrometry analysis of solid-phase micro-extraction from virgin fumigated C. cinensis females revealed that the PH3 LC25 (the lethal concentration required to kill the 25% of the population) fumigated female C. chinensis released significantly less amount of the pheromone components. In contrast, EF LC25 exposure did not affect the pheromone release. This study unveils the facts that the EF and PH3 fumigation have detrimental bioactivities against C. chinensis. Notably, this suggests to consider the sub-lethal EF and PH3 fumigation rather than the dose required to instantly kill all the C. chinensis individuals for disinfestation of stored adzuki bean.

Fumigant Activity of Ethyl Formate against the Chestnut Weevil, Curculio sikkimensis Heller.

Castanea crenata Siebold & Zucc. (Fagales: Fagaceae), a species of chestnut native to Korea and Japan, is distributed in Korea, Japan, and northeastern China, where chestnuts are a major economic agroforest product. Curculio spp. is among the main known pests of chestnuts around the world. In Korea, only phosphine (PH3) is permitted for the fumigation of C. sikkimensis larva-infested chestnuts. However, it is applied for large-scale fumigation, and its use is restricted. Moreover, it requires a long exposure time and an application device; thus, it cannot be used by small-scale farmers. In this study, the activity of ethyl formate (EF) as a fumigant against Curculio sikkimensis in chestnuts was investigated, and its potential for practical use by farmers was evaluated. The sorption of EF according to the filling ratio (FR) and fumigation time was tested, and the results revealed that 2.5% FR was the most effective. For C. sikkimensis in chestnuts, the mortality rate increased proportionately with the dose of EF. After exposure to 160 g/m3 of EF in a 12 L desiccator, the adult C. sikkimensis showed 100% mortality. According to the time-dose mortality data collected over 12 h of fumigation, the LCT90 and LCT99 values were estimated as 1052.0 and 1952.0 g·h/m3. The results revealed that immersion was not an effective method for controlling C. sikkimensis. According to the LCT values, a dose of 180.0 g/m3 and 12 h of fumigation resulted in 100% mortality on a small scale (2 m3). The results of this experiment indicate that EF could be conveniently used as a fumigant by farmers.

Effect of storage conditions on the shelf-life extension of fungus-colonized substrates based on Metarhizium anisopliae using modified atmosphere packaging.

Metarhizium anisopliae is a promising alternative to chemical pesticides against pine wilt disease caused by Bursaphelenchus xylophilus. Herein, we investigated the efficacy of modified atmosphere packaging (MAP) to prolong the shelf-life of the M. anisopliae conidia. The effects of various conditions on its stability were also examined. M. anisopliae-inoculated millet grains were treated in a MAP system with different packaging materials (polypropylene, PP; polyethylene terephthalate, PET; ethylene vinyl alcohol, EVOH), gas compositions (high CO2 atmosphere, ≈ 90%; high O2 atmosphere, > 95%; high N2 atmosphere, > 95%; 30% CO2 + 70% N2; 50% CO2 + 50% N2; 70% CO2 + 30% N2), and storage temperatures (4 and 25 °C). Results revealed EVOH film as the best for the preservation of gases at all concentrations for 28 days. MAP treatment in the high-barrier EVOH film under an atmosphere of 30% CO2 + 70% N2 achieved 80.5% viability of dried conidia (7.4% moisture content), with 44.2-64.9% viability recorded with the other treatments. Cold storage for technical concentrates formulation promoted extension of shelf-life of MAP-treated conidia. These results imply that MAP under optimized conditions could enhance the shelf-life of fungus-based biopesticides in fungus-colonized substrates formulations.

New discovery on the nematode activity of aureothin and alloaureothin isolated from endophytic bacteria Streptomyces sp. AE170020.

Endophytic bacteria, a rich source of bioactive secondary metabolites, are ideal candidates for environmentally benign agents. In this study, an endophytic strain, Streptomyces sp. AE170020, was isolated and selected for the purification of nematicidal substances based on its high nematicidal activity. Two highly active components, aureothin and alloaureothin, were identified, and their chemical structures were determined using spectroscopic analysis. Both compounds suppressed the growth, reproduction, and behavior of Bursaphelenchus xylophilus. In in vivo experiments, the extracts of strain Streptomyces sp. AE170020 effectively suppressed the development of pine wilt disease in 4-year-old plants of Pinus densiflora. The potency of secondary metabolites isolated from endophytic strains suggests applications in controlling Bursaphelenchus xylophilus and opens an avenue for further research on exploring bioactive substances against the pine wood nematode.

Larvicidal activity of Myrtaceae essential oils and their components against Aedes aegypti, acute toxicity on Daphnia magna, and aqueous residue.

The larvicidal activity of 11 Myrtaceae essential oils and their constituents was evaluated against Aedes aegypti L. Of the 11, Melaleuca linariifolia Sm., Melaleuca dissitiflora F. Muell., Melaleuca quinquenervia (Cav.) S. T. Blake, and Eucalyptus globulus Labill oils at 0.1 mg/ml exhibited > or = 80% larval mortality. At this same concentration, the individual constituents tested, allyl isothiocyanate, alpha-terpinene, p-cymene, (+)-limonene, (-)-limonene, gamma-terpinene, and (E)-nerolidol, resulted in > or = 95% mortality. We also tested the acute toxicity of these four active oils earlier mentioned and their constituents against Daphnia magna Straus. M. linariifolia and allyl isothiocyanate was the most toxic to D. magna. Twodays after treatment, residues of M. dissitiflora, M. linariifolia, M. quinquenervia, and E. globulus oils in water were 55.4, 46.6, 32.4, and 14.8%, respectively. Less than 10% of allyl isothiocyanate, alpha-terpinene, p-cymene, (-)-limonene, (+)-limonene, and gamma-terpinene was detected in the water at 2 d after treatment. Our results indicated that oils and their constituents could easily volatilize in water within a few days after application, thus minimizing their effect on the aqueous ecosystem. Therefore, Myrtaceae essential oils and their constituents could be developed as control agents against mosquito larvae.

Diel Rhythmicity of Field Responses to Synthetic Pheromone Lures in the Pine Sawyer Monochamus saltuarius.

The pine wood nematode (PWN), Bursaphelenchus xylophilus, causes lethal pine wilt disease (PWD) in Asia and Europe and has become a serious threat to global pine forest ecosystems. In Korea, Monochamus saltuarius transmits PWN not only to Pinus densiflora, but also to Pinus koraiensis, which is widely distributed across eastern Asia. The diel rhythmicity of M. saltuarius in response to its aggregation pheromone was studied with the aim of providing reliable data for the prevention of PWD and control of Monochamus spp. Using a spray dispenser controlled with an electronic timer, M. saltuarius pheromone and attractants (PA) were sprayed to determine the diel rhythm of the response to PA. The spraying period was divided into four time periods: 05:00-11:00 (time period A), 11:00-17:00 (time period B), 17:00-23:00 (time period C), and 23:00-05:00 (time period D). The largest number of M. saltuarius was caught in time period B, followed by A, C, and D. It could be concluded that the flight activity of M. saltuarius in response to PA was diurnal. The results of this study improve the understanding of the behavioral biology of M. saltuarius, allowing for the development of pest management strategies to prevent the spread of PWN and control its vector.

Nematicidal Activity of Benzyloxyalkanols against Pine Wood Nematode.

Pine wilt disease (PWD) is caused by the pine wood nematode (PWN; Bursaphelenchus xylophilus) and causes severe environmental damage to global pine forest ecosystems. The current strategies used to control PWN are mainly chemical treatments. However, the continuous use of these reagents could result in the development of pesticide-resistant nematodes. Therefore, the present study was undertaken to find potential alternatives to the currently used PWN control agents abamectin and emamectin. Benzyloxyalkanols (BzOROH; R = C2-C9) were synthesized and the nematicidal activity of the synthetic compounds was investigated. Enzymatic inhibitory assays (acetylcholinesterase (AChE) and glutathione S-transferase (GST)) were performed with BzOC8OH and BzOC9OH to understand their mode of action. The benzyloxyalkanols showed higher nematicidal activity than did benzyl alcohol. Among the tested BzOROHs, BzC8OH and BzC9OH showed the strongest nematicidal activity. The LD50 values of BzC8OH and BzC9OH were 246.1 and 158.0 ppm, respectively. No enzyme inhibitory activity was observed for BzC8OH and BzC9OH. The results suggested that benzyloxyalcohols could be an alternative nematicidal agent.