Infestation by Phorid Flies Disrupts Behavior and Immune Function in Honey Bees Monitored by Radio-frequency Identification.

Honey bees (Apis mellifera Linnaeus) are important pollinators in natural and agricultural ecosystems and play a key role in global food production. However, colonies are increasingly affected by multiple stressors, including emerging parasites, which can compromise their health and performance. Among these, phorid flies (Diptera: Phoridae) have been observed in association with weak or collapsing honey bee colonies in various regions in Mexico, yet their effects on honey bee behavior and immune function under field conditions remain poorly understood. In this study, we investigated the impact of a phorid fly infestation on the behavior, survival, and immune defense of A. mellifera under natural conditions. Using radio-frequency identification (RFID) technology, we monitored the daily activity of individually tagged bees from a healthy hive and a naturally infested hive. Additionally, we assessed the prevalence of coinfections and measured immune responses including prophenoloxidase (proPO), phenoloxidase (PO), lytic activity, and hemocyte counts. Our results showed that phorid fly infestation was associated with a reduction in the frequency and duration of foraging trips, nocturnal activity, and significant changes in immune function, particularly elevated proPO/PO activity and reduced total hemocyte counts. No significant differences were observed between adult and pupal stages in immune parameters, suggesting a consistent physiological response across developmental stages. While only one hive was infested and ultimately collapsed, these findings provide evidence that phorid flies can disrupt key behavioral and immune processes in honey bees. Further studies are needed to determine the broader implications of phorid infestations for colony health and resilience.