Ultrastructural Analysis of Johnston’s Organ and Brain Organization in Philaenus spumarius (Hemiptera: Aphrophoridae)

TL;DR

This study explores how the spittlebug Philaenus spumarius uses a simplified sensory system to effectively communicate and navigate, focusing on its brain and antennal structures.

Contribution

The study reveals how a reduced sensory system in P. spumarius is adapted for efficient communication and movement through specific neural organization.

Findings

P. spumarius integrates limited sensory input through a specialized neural organization.

The brain's primary neuropils support effective communication despite reduced antennal structures.

Antennal nerve pathways were traced to the central nervous system, revealing adaptation mechanisms.

Abstract

The spittlebug Philaenus spumarius is a key vector of a plant-pathogenic bacterium and mostly depends on its antennae to detect environmental and inter/intraspecific stimuli. Compared with many other insects, P. spumarius shows a reduced number of antennal sensory structures, but despite of this, it can efficiently orient and communicate. This study investigates how such a simplified sensory system is reflected in the organization of its brain by examining the fine structure of Johnston’s organ and analyzing the main regions of the brain. We also traced the pathways of antennal nerves up to the central nervous system. The results show how P. spumarius integrates limited sensory input through a neural organization that supports effective communication and movement. These findings provide insight into how insects can adapt their nervous systems to different sensory abilities, giving a basic knowledge for further behavioral and chemical ecology studies of this harmful pest.

Insects rely on a variety of sensory cues for orientation, with antennae playing a central role in receiving and transmitting information about the environment. Philaenus spumarius (Hemiptera: Aphrophoridae), a spittlebug and vector of the bacterium Xylella fastidiosa, has a reduced number of antennal sensilla, yet demonstrates effective multimodal communication through olfactory and vibrational signals. This study aimed to investigate how the simplified sensory system of P. spumarius relates to the primary neuropils of the brain. We examined the ultrastructural organization of Johnston’s organ using scanning and transmission electron microscopy, complemented by previous data on antennal sensilla. Brain organization was investigated by Micro-CT and confocal laser scanning microscopy, which enabled us to identify the primary neuropiles. In addition, we conducted antennal and single sensillum backfills to trace sensory neurons to the brain. Our findings provide insight into the adaptation of a simplified sensory system for effective communication and orientation in P. spumarius.

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