Comparative Bioactivity of Emamectin Benzoate Formulations against the Pine Wood Nematode, Bursaphelenchus xylophilus

Abstract

The pine wood nematode (PWN), <i>Bursaphelenchus xylophilus</i> is a well-known devastating pathogen of economic importance in the Republic of Korea and other countries. In the Republic of Korea, trunk injection of nematicides is the preferred method of control. In this study, the efficacy of 16 locally produced formulations of emamectin benzoate against the PWN are compared through determining their sublethal toxicities and reproduction inhibition potentials. Nematodes were treated with varying concentrations of the tested chemicals in multi-well culture plates, and rates of paralysis and mortality were determined after 24 h. Reproduction inhibition potential was tested by inoculating pre-treated nematodes onto <i>Botrytis cinerea</i>, and in pine twig cuttings. Despite the uniformity in the concentration of the active ingredient, efficacy was contrastingly different among formulations. The formulations evidently conformed to three distinct groups based on similarities in sublethal activity (group 1: LC<sub>95</sub> of 0.00768-0.01443 mg/ml; group 2: LC<sub>95</sub> of 0.03202-0.07236 mg/ml, and group 3: LC<sub>95</sub> of as high as 0.30643-0.40811 mg/ml). Nematode paralysis generally occurred at the application dose of 0.0134-0.1075 μg/ml, and there were significant differences in nematode paralysis rates among the products. Nematode reproduction was only evident at lower doses both on <i>B. cinerea</i> and pine twigs, albeit the variations among formulations. Group 1 formulations significantly reduced nematode reproduction even at a lower dose of 0.001075 µg/ml. The variations in efficacy might be attributed to differences in inert ingredients. Therefore, there is need to analyze the potential antagonistic effects of the large number of additives used in formulations.

The Potency of Abamectin Formulations against the Pine Wood Nematode, Bursaphelenchus xylophilus

“…And when compared with the least effective formulation among the tested compounds, abamectin-sulfoxaflor mixed formulation was remarkably over hundred times more potent (LC 50 = 0.00285 vs. 0.39462 mg/ml) despite the similarity in abamectin content (1.8%). Similar results detailing significant disparities in the performance of various formulations of emamectin benzoate against the PWN have already been reported ( Lee et al, 2023 ).…”

“…This may lead to production of final formulations possessing substantially altered or different potency ( Beggel et al, 2010 ; Schmuck et al, 1994 ). In our recent study on the efficacy of emamectin formulations against the PWN ( Lee et al, 2023 ), we uncovered the significant disparities in the performance of various formulations of similar active ingredient strength against the PWN. In the current study, the potency of various abamectin formulations against the PWN is equally evaluated by determining their sublethal toxicity levels, and the potential to inhibit nematode reproduction after pre-exposure of the nematode populations.…”

Phytochemical Volatiles as Potential Bionematicides with Safer Ecotoxicological Properties

“…Other currently used nematicides are obtained from the de novo design of natural compounds, e.g., avermectins, which derive from a fermentation process by the soil-dwelling actinomycete, Streptomyces avermitilis [ 13 ]. The hemisynthetic emamectin, from the avermectin family of compounds, is successfully employed against the pinewood nematode Bursaphelenchus xylophilus , a forest pathogen [ 14 ]. More recently, a next generation of synthetic nematicides, including fluazaindolizine, fluensulfone, or fluopyram, has been introduced that shows safer (eco)toxicological parameters [ 15 ]; however, their modes of action are still scarcely understood [ 1 ], which makes pinpointing the risks to agroecosystems a difficult task.…”

Mathematical Modeling and Stability Analysis of the Delayed Pine Wilt Disease Model Related to Prevention and Control

“…Presently, global strategies for PWD prevention and control encompass chemical control, physical control, biological control and biomimetic technology, with avermectin (AVM) as a predominant insecticidal agent [11]. Lee et al [12] conducted comparative analyses on 16 avermectin benzoate formulations against PWD to support disease control. Alvarez et al [13] engineered diverse trap designs assessing their efficacy in maximizing the attraction and retention of live insects through field experiments and comparative modeling.…”