Antennal morphology and ultrastructure of the New Zealand endemic mayfly, Coloburiscus humeralis

Mayflies (Order: Ephemeroptera) are the most basally branching winged insect group within the Hexapoda. They have three life stages: an exclusively aquatic nymph stage, a sexually immature winged subimago, and a sexually mature winged imago. We conducted an ultrastructure study of the antennae of all three life stages of Coloburiscus humeralis using Scanning Electron Microscopy (SEM). Differences in the cuticular surface of their antennae were observed across the three life stages. Numerous sensilla were identified, including sensilla trichodea, sensilla basiconica, and sensilla coeloconica, known to have roles in chemoreception, mechanoreception, thermoreception, and hygroreception. The antennae of different life stages housed various types of sensilla, which are probably reflective of the changes in sensory modalities associated with the distinct environments they inhabit. Sexual dimorphism was observed between antennae of winged life stages, with some types of sensilla found exclusively on the antenna of the female subimagos and imagos, suggesting they may play a role in supporting female-specific olfactory behaviours. This research contributes to further understanding how insects with life stages that occupy different habitats fulfil various sensory tasks.