Seasonal dynamics of honey bee pathogens and Varroa destructor infestation in South Korea: results from a National...

Honey bee colony losses are an increasing global concern, yet nationwide pathogen-resolved surveillance data integrating molecular diagnostics with field-based mite monitoring remain limited. This study presents the first national active surveillance program for honey bee diseases in South Korea, combining standardized field inspections with RT-qPCR-based pathogen detection. A total of 1,715 samples were collected from 107 apiaries during three seasonal surveillance rounds in 2025: Round 1 (post-overwintering; March-May), Round 2 (post-honey-harvest; July-August), and Round 3 (pre-overwintering; October-November). Both Apis mellifera and Apis cerana colonies were included in the analysis. Fourteen target honey bee pathogens were screened using RT-qPCR assays (Ct ≤ 35), and Varroa destructor infestation status in A. mellifera apiaries was evaluated through brood inspection or powdered-sugar roll testing depending on seasonal field conditions. DWV prevalence increased progressively from 70.1% in Round 1 (post-overwintering) to 90.4% in Round 2 (post-honey-harvest) and 97.0% in Round 3 (pre-overwintering), coinciding with increasing Varroa detection in A. mellifera apiaries (28.1%, 85.4%, and 87.9%, respectively). Israeli acute paralysis virus (IAPV) also increased progressively across the three surveillance rounds (18.3%, 40.1%, and 47.7%). In contrast, black queen cell virus (BQCV), sacbrood virus (SBV), Vairimorpha spp. (formerly Nosema spp.), and chalkbrood showed declining trends toward autumn. Co-infection patterns shifted seasonally. Although the mean number of detected pathogens per sample decreased from 2.76 to 2.02, co-detection of DWV and IAPV increased markedly from 15.3% to 47.0%. In A. cerana apiaries, SBV remained highly prevalent throughout the surveillance rounds. These findings indicate that the late-season expansion of the Varroa-DWV-IAPV complex represents a major epidemiological feature of Korean apiculture and coincides with the critical period of winter-bee production. This nationwide surveillance framework provides an evidence-based foundation for seasonal honey bee disease management and optimized timing of Varroa control interventions in temperate apicultural systems.