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

The pine wood nematode (PWN), Bursaphelenchus xylophilus is a well-known devastating pathogen of eco-nomic 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 re-production inhibition potentials. Nematodes were treat-ed with varying concentrations of the tested chemicals in multi-well culture plates, and rates of paralysis and mortality were determined after 24 h. Reproduction in-hibition potential was tested by inoculating pre-treated nematodes onto Botrytis cinerea, and in pine twig cut-tings. Despite the uniformity in the concentration of the active ingredient, efficacy was contrastingly different among formulations. The formulations evidently con-formed to three distinct groups based on similarities in sublethal activity (group 1: LC95 of 0.00768-0.01443 mg/ ml; group 2: LC95 of 0.03202-0.07236 mg/ml, and group 3: LC95 of as high as 0.30643-0.40811 mg/ml). Nematode paralysis generally occurred at the application dose of 0.0134-0.1075 mu g/ml, and there were significant differ-ences in nematode paralysis rates among the products. Nematode reproduction was only evident at lower doses both on B. cinerea and pine twigs, albeit the variations among formulations. Group 1 formulations significant-ly reduced nematode reproduction even at a lower dose of 0.001075 mu g/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.