Genetic and Transcriptomic Basis of Enhanced Nectar and Resin Foraging in Honey Bees

The collection of honey and propolis is crucial for the nutrition and health of honey bee colonies. In this study, Apis mellifera with high productivity for both honey and propolis (MJ) was developed through long-term selective breeding using Apis mellifera caucasica and Apis mellifera carnica as breeding materials, resulting in substantial improvements in both honey yield and propolis production. To elucidate the genetic basis and molecular mechanisms underlying efficient foraging behavior for nectar and resins in honey bees, whole-genome resequencing was performed on MJ, the C-lineage, and the O-lineage of Apis mellifera. In addition, transcriptome sequencing was conducted using MJ and Apis mellifera ligustrica, which exhibited the highest honey and propolis production traits. MJ had a composite genetic background dominated by O-lineage ancestry. Compared with C-lineage honey bees, MJ exhibited 234 candidate genes under selection, mainly related to chitin and amino sugar metabolism. Transcriptome analysis identified 504 and 2676 differentially expressed genes between MJ and Italian honey bees in the nectar-forager and resin-forager comparisons, respectively, involving chemosensory gene families. Genes upregulated in MJ nectar and resin foragers were mainly associated with redox regulation and energy metabolism, respectively. Integrated analyses identified 7 candidate genes associated with nectar foraging and 41 candidate genes associated with resin foraging; these genes were involved in chemosensory responsiveness, flight-related structural traits, energy metabolism, and redox regulation in MJ. These findings provide genetic and transcriptomic resources for further studies on the division of labor in foraging and molecular breeding in honey bees.