Establishment and application of bioassay- and molecular marker-based methods for monitoring fluvalinate resistance of Varroa mites

Rapid spread of Amitraz resistance linked to a unique T115N mutation in the octopamine receptor of Varroa mites in Korea

The Varroa mite, Varroa destructor, is an ectoparasitic pest of Western honey bees and poses a significant threat to apiculture. In Korea, widespread fluvalinate resistance has increased reliance on amitraz as an alternative acaricide. This study identified a novel mutation, T115N, in the β2-adrenergic-like octopamine receptor gene (Octβ2R) and confirmed its role in amitraz resistance. Genotyping of individual mites, based on time-dependent intoxication responses to a diagnostic dose of amitraz, revealed a strong correlation between genotype and resistance phenotype: mites with early intoxication responses were homozygous for the T115 allele, whereas those with delayed responses predominantly carried the homozygous N115 allele. Mites with homozygous N115 genotype exhibited a median lethal time approximately 2.8-fold longer than their T115 counterparts, confirming the resistance conferred by the T115N mutation. Quantitative sequencing was established to track the spread dynamics of T115N mutation in Korean Varroa mite populations over five years (2020-2024). While the mutation was rare from 2020 to 2022, its frequency increased sharply in 2023 and became widespread across Korea by 2024, coinciding with increased amitraz usage. These findings suggest region-specific selection for the T115N mutation driven by amitraz exposure.

The status of pyrethroid resistance mutation frequencies in Varroa destructor populations in the most important beekeeping areas of Türkiye

The Varroa destructor (hereafter referred to as Varroa) is a major pest of honeybees that is generally controlled using pyrethroid-based acaricides. However, resistance to these insecticides has become a growing problem, driven by the acquisition of knockdown resistance (kdr) mutations in the mite's voltage-gated sodium channel (vgsc) gene. Resistance mutations in the vgsc gene, such as the L925V mutation, can confer resistance to pyrethroids like flumethrin and tau-fluvalinate. Monitoring genotypic resistance through molecular mutation screening is crucial for tracking and mitigating resistance spread. In this study, the frequency of resistance mutations in the vgsc was examined using a Polymerase Chain Reaction-Restriction Fragment Length Polymorphism (PCR-RFLP) approach in Varroa populations sampled throughout the Mediterranean, Aegean, and Black Sea regions of Türkiye. Considering all the samples analyzed, the results demonstrated a mean resistance allele frequency of 83.29%, indicating a relatively high frequency of resistant alleles. We observed 94.58%, 85.71%, and 69.58% resistant allele frequencies in populations sampled from the Mediterranean, Aegean, and Black Sea regions, respectively, in our study. The results of our investigation demonstrated substantial regional variations in the frequencies of resistant alleles among Varroa populations throughout Türkiye, with notably elevated resistance levels observed in the Mediterranean and Aegean regions. Due to the significant resistance mutation frequency differences between both provinces and regions, long-term monitoring of resistance alleles and the planning of regional control strategies are required for effective control of this pest.

Prevalence of pathogens in abnormal honey bees in South Korea, 2020-2023

South Korea's beekeeping industry has been facing a major crisis due to colony collapse disorder (CCD), manifesting since the winter of 2021. CCD in South Korea is presumed to be caused by a combination of factors, including an abnormal climate, pesticide use, declining source plants, and increased honey bee diseases. We examined the prevalence of 12 major honey bee (Apis mellifera) pathogens by sampling 3,707 colonies with abnormal behavior and suspected pathogen infections from 1,378 apiaries nationwide between 2020 and 2023. Black queen cell virus (BQCV), deformed wing virus (DWV), Israeli acute paralysis virus (IAPV), and Vairimorpha (Nosema) ceranae had the highest infection rates among honey bees in South Korea. BQCV had the highest infection rate (83.3% in 2023) and was highly prevalent throughout the year, regardless of the season. DWV (48.7%) and IAPV (41.3%) had the highest infection rates in October-December, corresponding to the winter season. Among the 12 honey bee pathogens, acute bee paralysis virus and Kashmir bee virus were rarely detected; the remaining 10 honey bee pathogens were detected throughout the year. The differences in honey bee pathogen prevalence among regions were not significant. We suggest that South Korean honey bees are highly exposed to viral pathogens, possibly resulting in the loss of unhealthy honey bees during the winter. Our study is expected to help identify trends in the occurrence of honey bee pathogens in South Korea and predict outbreaks to prepare a prevention system and appropriate control measures for honey bee pathogens.

Investigation of resistance against to flumethrin using against Varroa destructor in Türkiye

The honeybee ectoparasite Varroa destructor is a major threat to apiculture when evaluating bee diseases and pests. While attempting to control this mite, beekeepers often depend on a small selection of authorized synthetic acaricides, such as flumethrin, which is widely used in Türkiye and globally. However, resistance to flumethrin develops due to incorrect and excessive use. In this study conducted at Ordu Beekeeping Research Institute, trial group were established including an untreated control group and group where flumethrin-based pesticides were applied. Dead varroas collected from pollen traps and live varroas collected from bees were obtained from these trial groups for molecular analysis as positive-negative controls. Varroa samples were collected from provinces representing different regions with intensive beekeeping activities such as Adana, Ankara, Bingöl, Muğla, Ordu, Şanlıurfa, Tekirdağ. Molecular methods were employed to investigate the resistance gene region for pyrethroids (specifically flumethrin) against V. destructor. In our study, individual DNA extractions were performed on dead parasites from colonies subjected to pyrethroid application (resistance negative control) and live parasites (resistance positive control). The DNA samples obtained were used in PCR reactions targeting the region encoding the 925th amino acid of the voltage-gated sodium channel (VGSC) gene, which is responsible for resistance formation. The DNA samples were subjected to gel electrophoresis to observe the amplification products of the expected target region. To examine the nucleotide sequence changes that encode leucine at the 925th amino acid, which is associated with resistance, DNA sequence analysis was applied to the amplification products. Out of 332 V. destructor parasites obtained from different provinces, 279 were analysed using molecular methods. It was observed that 31% of the samples showed sensitivity to flumethrin while 69% exhibited resistance to it. Among the resistant samples: 27% had homozygous isoleucine mutation; 28% had homozygous valine mutation; 2.8% had heterozygous isoleucine mutation; 8.5% had heterozygous valine mutation; and 2.8% had heterozygous methionine mutation, all of which were associated with flumethrin resistance. As a result, the rate of flumethrin resistance in parasites varied between 51% and 94% among different provinces.