The development of natural control agents against American foulbrood in honeybees

This study explored the effects of Cryptomeria japonica leaf essential oil (CjLEO) on honeybee health, focusing on both toxicity and gene expression regulation. At a low concentration of 10 ppm, CjLEO exhibited no acute toxicity but induced significant changes in gene expression, as revealed by next-generation transcriptome sequencing. Principal Component Analysis (PCA) and Differential Gene Expression (DEG) analysis identified over 9,000 genes with notable upregulation of immune-related genes such as hymenoptaecin, abaecin, and apidaecin, indicating an enhancement of immune pathways. Gene Ontology (GO) enrichment analysis highlighted that these genes were associated with defense and innate immune responses. For the experiments, healthy bee colonies free of mites and disease were selected, and one-day-old bees were reared in an incubator at 33 positive or negative 1 degree. Daily treatments of CjLEO in varying concentrations, with ethanol as a vehicle, were administered over 7 days, during which mortality was monitored and survival rates were calculated. Afterward, bee head tissues were homogenized, and RNA was extracted and purified using commercial kits, with quality assessed through Nanodrop 1000 Spectrophotometer v.3.5 (Thermo Scientific, USA) and Qubit 2.0 Fluorometer (Invitrogen, USA). The results demonstrated that while 10 ppm CjLEO posed no direct toxic effects, it had a significant regulatory impact on immune-related gene expression, suggesting its potential role in enhancing honeybee immunity.