Argyresthia Hübner, [1825] is a genus of small to medium sized glossy moths which comprises more than 200 species worldwide, but the Korean fauna includes only eight previously known species. In this study, we describe one new species, A. (Argyresthia) brevalbella sp. nov., and report A. (A.) angusta Moriuti, 1969 and A. (Blastotere) densa Liu, Wang et Li, 2017 for the first time from the country. The three species were found in Hallasan National Park located in the southernmost province Jeju-do at altitudes between 900–1,300 m. The new species is externally very similar to A. (A.) longalbella Liu, Wang et Li, 2017 in having a fuscous forewing with a white dorsal band, but can be distinguished by the shape of the valva, saccus and phallus of the male genitalia. We provide photographs of adults and genitalia, differential diagnoses and DNA barcodes for the three species.

Summary: Parkellus projectus n. sp. isolated from rhizospheric soils of a dead Abies koreana was characterised using morphometrics and molecular DNA data. It is characterised by its medium sized body 1.97-2.68 mm long; buccal cavity oval shaped, 1.9-2.1 times as long as wide (55.0-65.0 vs 28.0-33.0 μ m), dorsal tooth apex at 60-69% from anterior end of buccal cavity, vulva at 63.9-70.4% body length; presence of 1-3 prominent pre- and postvulval papillae, female tail 105-137 μ m long, sickle shaped, with 1-2 dorsal pores, tapering to a rounded terminus; males having ventral cuticular pores above and below secretory-excretory pore, and a series of precaudal cuticular pores on both ventral and dorsal side; spicules 95-110 μ m long, gubernaculum 27-30 μ m long; 19-22 ventromedian supplements, 1-2 pairs of caudal papillae and tail with 3-4 dorsal pores, curved ventrad, with its terminal portion variably, but visibly bent dorsad. Additionally, a population of Clarkus papillatus (Bastian, 1865) Jairajpuri, 1970 was morphologically characterised and DNA data supplied. The phylogenetic relationships among species were reconstructed using 18S-, 28S- and ITS-rRNA gene sequences. Inferences from the three genes showed well-supported sister relations of the new species with other members of the genus.

Summary: Prionchulus porosus n. sp. isolated from the bark and wood of a dead black pine tree was characterised using morphometrics and molecular DNA barcodes. It is characterised by its medium-sized body 2.14-2.70 mm long, numerous body pores, 115-135 in number, remarkably prominent, concentrated only on dorsal side, cephalic papillae more prominent than labial, buccal cavity 43.5-49.5 μ m long, amphidial aperture at the level of, or below, dorsal tooth apex, dorsal tooth apex located at 25.2-31.5% buccal cavity length, pars refringens vaginae with two well-developed semispherical or drop-shaped sclerotisations, vulva at 57.5-60.6% body length, tail 165-191 μ m long, plump, ventrally curved tapering to bulky broadly rounded terminus, with 5-8 dorsal pores. Additionally, populations of P. punctatus , Coomansus parvus , C. ulsani and Mylonchulus hawaiiensis were also morphologically characterised and DNA barcodes supplied. The phylogenetic relationships among species were reconstructed using 18S-, 28S- and ITS-rRNA gene sequences. Inferences from the three genes showed well-supported sister relations of Prionchulus porosus n. sp. with other members of the genus.

Summary: Bealius clavicaudatus n. sp. isolated from the bark and wood of a dead black pine tree was characterised using morphological, morphometric and molecular DNA data. It is characterised by body length of 1.01-1.16 mm (female), 0.66-0.8 mm (male) and 0.81-0.91 mm (pre-parasitic female), lateral field with six incisures, stylet with distinct asymmetrical knobs, 8.0-9.5 μ m long in female and male, and 12.0-14.0 μ m in pre-parasitic female, secretory-excretory pore at 6.0-14.0 μ m posterior to hemizonid, basal pharyngeal bulb large, saccate, with a short posterior stem-like extension opening into intestine dorsally, vulva a transverse slit, vulva lips protuberant, anterior lip thicker, sclerotised, partially extending over vulval slit, epiptygma present, post-uterine sac absent, body abruptly narrowing on vulval side posterior to vulva and expanding to form a club-like shape, with broadly rounded terminus in female, conical, with a finely rounded terminus in male, and subcylindrical with broadly rounded terminus in pre-parasitic female and spicules arcuate, 1.3-1.8 times tail length. The new species was morphologically compared with the three currently known species under the genus and typologically similar species under other relevant genera. The phylogenetic relationships were reconstructed using partial 18S- and 28S-rRNA gene sequences and the resultant topologies were discussed.

Elaeocarpus sylvestris (Lour.) Poir. var. ellipticus (Thunb.) H.Hara, an evergreen tree species native to Jeju Island, South Korea, has experienced a progressive decline associated with phytoplasma infection. This study aimed to evaluate the efficacy of oxytetracycline-based tree injection for suppressing phytoplasma and improving tree vitality. Two formulations—oxytetracycline hydrochloride (4.3%) and oxytetracycline calcium alkyltrimethyl ammonium (17%)—were administered to 40 infected individuals across two sites using a gravity-fed injection system. Treatment efficacy was evaluated based on chlorophyll content as an indicator of physiological recovery, while phytoplasma presence was assessed by PCR at 150 days after injection. The oxytetracycline hydrochloride group showed the highest suppression, with a 70% phytoplasma non-detection rate as determined by PCR analysis. Treated trees exhibited significantly higher chlorophyll content compared to untreated infected controls. These findings suggest that minimally invasive tree injection using oxytetracycline can provide temporary suppression of phytoplasma and support physiological recovery in E. sylvestris.