Deformed wing virus affects foraging success and foraging specialization of honeybee workers.

Deformed wing virus (DWV) is a major driver of honeybee colony losses, yet its sublethal effects on adult foraging behaviour remain underexplored. Building on evidence that covert DWV infections impair sucrose responsiveness and associative learning, we tested whether infection changes foraging success and specialization in worker bees. Using a controlled experiment, we marked 1,000 newly emerged workers that were either inoculated with DWV lysate or injected with an RNA-interference control that suppressed viral replication. Foraging activity, success, and specialization were recorded. Our results show that DWV-infected bees began foraging earlier ("precocious foraging") and had higher mortality, reducing their lifespan as foragers. Furthermore, infected nectar foragers were significantly less likely to return with nectar, and when they did, it contained markedly lower sugar concentrations compared to control bees. Conversely, infected bees were slightly more likely to return with pollen and showed greater specialization in pollen foraging, although pollen load weights were similar between treatments. These findings indicate that DWV disrupts multiple aspects of foraging ecology by accelerating behavioural maturation, shortening forager lifespan, reducing nectar yield and quality, and shifting resource preference towards pollen. Such changes may reflect a compensatory response to impaired nectar collection, but nonetheless could compromise colony nutrition, particularly when high-quality nectar is scarce. Our results align with previous work linking DWV to impaired foraging efficiency, and altered foraging specialization, and reduced honeybee survival, underscoring DWV's substantial sublethal costs. By reducing nectar foraging while leaving pollen loads unaffected, DWV may limit honey stores and brood rearing during high demand periods, contributing to seasonal losses. Even moderate declines in nectar-foraging can undermine colony resilience, highlighting the need to address DWV's role in the pollinator crisis.