American Society of Naturalists

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“Combinatorial signal processing in an insect”

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Bretta Speck, Sara Seidita, Samuel Belo, Samuel Johnson, Caley Conley, Camille Desjonquères, and Rafael L. Rodríguez (Oct 2020)

A playback experiment shows that female Enchenopa treehoppers are capable of basic combinatorial signal processing

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An aggregation of <i>Enchenopa binotata</i> treehoppers in the University of Wisconsin–Milwaukee’s Greenhouse.<br/><br />(Credit: Bretta Speck)
An aggregation of Enchenopa binotata treehoppers in the University of Wisconsin–Milwaukee’s Greenhouse.
(Credit: Bretta Speck)

How much information can a tiny insect process? Animals with large brains are capable of processing complex, multi-component mating signals. Researchers at the University of Wisconsin-Milwaukee have found an insect with similar signal processing capabilities. Enchenopa binotata, a species of treehopper native to Wisconsin, communicate vibrationally through the branches of the Viburnum lentago trees they live on. Males seeking a mate will tap out a “whine-pulse” signal to attract females. Researchers presented female treehoppers with male signals that varied in signal composition. They found that the females were capable of discriminating between the signals and responding accordingly; thus helping to understand signal processing capabilities by animals with small brains.


Human language is combinatorial: phonemes are grouped into syllables, syllables into words, and so on. The capacity for combinatorial processing is present to different degrees in some mammals and birds. We used a vibrational insect, Enchenopa treehoppers, to test the hypothesis of basic combinatorial processing against two competing hypotheses: beginning rule (where the early signal portions play a stronger role in acceptability); and no ordering rule (where the order of signal elements plays no role in signal acceptability). Enchenopa males use plant-borne vibrational signals that consist of a whine followed by pulses (WP). We tested the above hypotheses with vibrational playback experiments in which we presented Enchenopa females with stimuli varying in signal element combinations. We monitored female responses to these playbacks with laser vibrometry. We found strong support for combinatorial processing in Enchenopa: in brief, females preferred natural-combination signals regardless of the beginning element and discriminated against reverse-order signals or individual elements. Finding support for the combinatorial rule hypothesis in an insects suggests that this capability represents a common solution to the problems presented by complex communication.