Natural viral infection, individual immunity, and flight performance in honey bee Apis mellifera drones

In honey bees, drones' flight ability is crucial for their mating success. In this study, we assessed the flight ability of drones from three age cohorts (1-3 weeks old) by flight mill and subsequently examined their sexual development and status, viral infection by deformed wing viruses type A and B (DWV-A, DWV-B) and Israeli acute paralysis virus (IAPV) and expression of six immune genes by RT-qPCR. Sexually matured drones flew longer distances compared to immature drones. Infections of DWV-A and IAPV were common in drones, but their impact on drone flight differed. Flight distance and speed were negatively correlated with loads of IAPV and DWV-B, respectively, in 14- to 15-day-old drones, but not in 7 days old. Flight speed was negatively correlated with the expression of protein lethal 2 (Pl2) and peptidoglycan recognition protein S2 (PGRP-S2) in 14- to 15-day-old drones. These findings suggest trade-off between a drone's flight performance and their immunity and/or the impact of virus infection on drones' flight ability.