Treehopper

Lore & Background

Treehoppers have long interested naturalists due to their unusual appearance, particularly their enlarged and ornate pronotum, which enhances camouflage or mimicry—often resembling plant thorns (hence the name 'thorn bugs'). The pronotal 'helmet' was suggested to be a serial homologue of insect wings, but this interpretation has been refuted by studies such as Mikó et al. (2012) and Yoshizawa (2012). Nymphs have a tube-like ninth abdominal segment through which the tenth and eleventh segments can be everted in defense or to provide honeydew to other animals.

Treehoppers feed on plant sap using pointy, tube-shaped mouthparts. Excess sap becomes honeydew, which attracts ants; some species have well-developed ant mutualisms, with ants providing protection from predators. Mutualisms also occur with wasps (e.g., Parachartergus apicalis) and geckos, which communicate via small abdominal vibrations. Nymphs of Publilia concava have higher survivorship in the presence of ants even without predators, possibly because uncollected honeydew promotes sooty mold that hinders excretion and photosynthesis.

Females lay eggs with a saw-like ovipositor into plant stems or leaves; eggs may be parasitized by fairyflies (Mymaridae) and Trichogrammatidae. Some females guard their eggs, buzzing wings at intruders, and gregarious species may cooperate in egg protection. In Publilia modesta, mothers attract ants when nymphs produce little honeydew. Most species are harmless to humans, but a few are minor pests, including Umbonia crassicornis, Spissistilus festinus, and Stictocephala bisonia (introduced to Europe).

Reader's Guide

Treehoppers are significant in evolutionary biology for their extreme pronotal diversity, which provides a model for studying camouflage and mimicry. Their mutualisms with ants, wasps, and geckos illustrate complex ecological interactions, including the feeding facilitation hypothesis, where ant collection of honeydew may reduce competition and increase feeding. The systematic arrangement remains tentative, with three main lineages: Endoiastinae (most ancient, resembling cicadas), Centrotinae, and the more apomorphic Darninae, Heteronotinae, Membracinae, and Smiliinae. Some proposed subfamilies (Centronodinae, Nicomiinae) may need merging into Centrotinae for monophyly. Despite limited research on diversity, treehoppers offer insights into insect morphology, behavior, and coevolution, with only a few species considered minor agricultural pests.

Did You Know?

• Treehoppers have specialized muscles in the hind femora that unfurl to generate sufficient force to jump.
• The buffalo treehopper (Stictocephala bisonia) has been introduced to Europe.