Functional anatomy of the precibarial valve in Philaenus spumarius (L.).

Sara Ruschioni,Nunzio Isidoro,Roberto Romani,Emanuele Ranieri,Paola Riolo,Rodrigo P P Almeida,Antonio Biondi

doi:10.1371/journal.pone.0213318

Sara Ruschioni, Nunzio Isidoro + Show 5 more

Open Access

https://doi.org/10.1371/journal.pone.0213318

Copy DOI

Abstract

In phytophagous sap-sucking insects, the precibarial valve plays an important role in sap ingestion. We used light and electron microspcopy to study the morphology and the ultrastructure of the precibarial valve of the meadow spittlebug, Philaenus spumarius (Hemiptera, Aphrophoridae), in order to better understand the operative mechanism of this structure. The precibarial valve revealed to be a complex structure with a bell-like invagination in the middle of the precibarium (on the epipharynx). Unlike the current hypothesis, we propose that the valve opens by dilator muscles and closes through cuticular and fluid tensions, the latter leading to morphological changes to the plane of the valve based on sap flow. Moreover, the presence of a precibarial secretory structure is described for the first time for auchenorrhynchan insects. In light of these observations, functions are hypothesized and discussed for this secretory structure.

Highlights

In phytophagous sap-sucking insects, mouthpart adaptations allow for feeding on hosts by inserting stylets into specific tissues [1,2,3,4]
Morphology of the precibarial valve In P. spumarius, the precibarium is formed by the juxtapositon of the hypopharynx and the epipharynx
Our observations with P. spumarius indicate that the precibarial valve is a complex structure, with a bell-like invagination located in the middle of the epipharynx, linked to a flap-like structure that pivot on it, attached to a muscle originating on the clypellus

Summary

Introduction

In phytophagous sap-sucking insects, mouthpart adaptations allow for feeding on hosts by inserting stylets into specific tissues (e.g. phloem, xylem) [1,2,3,4]. Active sap ingestion is made possible thanks to this diaphragm pump [5,6]. When these muscles contract the diaphragm elevates, the pump volume increases, and the pressure lowers within the chamber relative to the sap on which the insect is feeding [6,7,8,9]. The region of the alimentary canal between the divergence point of the stylets and the cibarium is termed precibarium. This canal is formed by the apposition of the epi- and hypopharynges [6,10,11,12,13].

Methods

Results

Conclusion