# New Insight and Confrontation of the Internal Structure and Sensilla of the Mouthparts of Cicadomorpha (Insecta: Hemiptera)

## TL;DR

This study examines the mouthparts of cicadomorphan insects, revealing conserved structures for sap feeding and diverse sensory adaptations for interacting with host plants.

## Contribution

The study provides new insights into the microstructural and sensory adaptations of Cicadomorpha mouthparts, highlighting both conserved and specialized traits.

## Key findings

- The mouthparts of cicadomorphan insects show a conserved structure with a dual interlocking maxillary stylet system.
- Variations in mandibular barbs and salivary canal closure types suggest adaptations to different host plant tissues.
- The labial tip hosts diverse sensilla types, including gustatory, olfactory, and thermo-higroreceptors, aiding in host detection and feeding.

## Abstract

The microstructural examination of Cicadomorpha mouthparts reveals a similar morphological framework in the studied species, essential for sap feeding from floem, xylem, or epidermis cells. The consistent presence of the dual interlocking maxillary stylet system and overall mouthpart architecture underscores evolutionary stability within the group. In contrast, variations in mandibular barbs, salivary canal closure types, and the diversity of sensilla on the labial tip (contact chemoreceptor, gustatory, olfactory, and thermo-higroreceptors) suggest functional adaptations to different host plant interactions. These findings contribute to a deeper understanding of the morphology and sensory differences in Cicadomorpha.

This study presents detailed microstructural observations of the mouthparts and sensory organs of adult cicadomorphan species, obtained using scanning electron microscopy (SEM). Despite microstructural variation, the overall morphology of the mouthparts, comprising a three-segmented labium and a bundle of interlocking stylets (maxillae and mandibles), is highly conserved across species, supporting its evolutionary significance in sap feeding from floem, xylem, or epidermis cells. Variations in the number and shape of mandibular stylet barbs likely reflect adaptations to different host plant tissues. The presence of an identical dual interlocking system between the maxillary stylets, which is found consistently across taxa, enhances functional stability during feeding and indicates a conserved mechanism among cicadomorphans. The species studied exhibit two distinct types of salivary canal closure: hooked and T-shaped. The latter potentially represents a state linked to specialised feeding strategies, such as sap xylem feeding. On the labial tip, there are different shapes of the anterior sensory fields. This area hosts a complex array of sensilla of different numbers, including gustatory (sensilla peg, PS1 and PS2, basiconica, BS3, double basiconica, DB), olfactory (finger–like, FLS) and thermo-hygroreceptive (sensillum dome-shaped, DS, and coeloconicum, CS) types, which facilitate host detection and feeding site selection. In the posterior sensory field, sensilla contact-chemosensory (sensilla basiconica, BS1 and BS2, and sensillum trichoideum, TS) are present. Mechanosensilla chaetica (CH1–CH3) are widely distributed on the last labial segment and may contribute to labium positioning. These findings emphasise the presence of both conserved and specialised morphological traits reflecting evolutionary and ecological diversification within Cicadomorpha.