Abundance of immature <i>Culicoides</i> (Diptera: Ceratopogonidae) and tidal dynamics on an Amazon coastal zone sandy beach

The smallest hematophagous insects in the world belong to the genus Culicoides Latreille, which are vectors of various diseases. These insects are frequent pests on sandy beaches, with immature stages often found in flooded upper areas, edges of brackish waters, and intertidal zones of mangroves, mainly concentrated above the mean water level. In this study we investigated the presence of Culicoides larvae across extensive distances in the intertidal zone of an Amazonian sandy beach-a challenging, high energy, and macrotidal environment with fine sediment. Local community reports link biting midge infestations to neap tides. Hence, this study aimed to determine whether larvae found across the beach intertidal area were associated with these infestations and their periodicity. Samples were collected daily over a two-week period spanning a semidiurnal tidal cycle, down to 150 m below the mean high-tide line, at three distances (every 50 m). Immature individuals occurred at all levels, with abundance about three times higher at 50 m below the waterline. Interestingly, larval abundance was significantly higher during spring tides than during neap tides (when none were recorded), despite the harsh nature of this high-energy, macrotidal environment-especially during spring tides. The tidal cycle pattern of immatures was opposite to that observed in adults and consistent with local community reports. Adults that emerged from reared immatures, as well as those collected using human bait, were identified as C. phlebotomus. This information may benefit further studies and tourism management by helping visitors plan trips to avoid periods of peak biting midge activity.