Elytral microstructures and wettability properties in neotropical aquatic beetles

In beetles, the elytra play critical roles in wing protection, locomotion, and communication, and their surface properties vary across ecological gradients. To explore the characteristics of the elytral surface on aquatic beetles, their microstructure and wettability, we studied six Neotropical species from the families Dytiscidae (Rhantus souzannae and Laccophilus fasciatus), Hydrophilidae (Tropisternus chalybeus and Tropisternus cf. mergus) and Gyrinidae (Gyrinus costaricensis and Dineutus solitarius), representing different habitats and trophic groups. We used scanning electron microscopy, profilometry and contact angle measurements to characterize the elytra surface and wettability properties. Elytral microstructures varied among species, both species of Gyrinidae and Dytiscidae exhibited more complex elytral structures including micro-reticulation (polygonal patterns) and strial reticulation for G. costaricensis. Hydrophilidae species presented a smooth elytral surface without polygonal patterns and showed the lowest roughness value for T. cf mergus with 0.594 μm, compared to D. solitarius with roughness of 2.776 μm. Although contact angles did not differ significantly among species, all exceeded 90°, indicating overall hydrophobic features. The microstructural diversity and water-repellent properties documented provide key insights into the biology of the group and offer valuable foundation for futures studies in functional biology and biomimetics.