Survival Sounds in Insects: Diversity, Function, and Evolution

Abstract

Insect defense sounds have been reported for centuries. Yet, aside from the well-studied anti-bat sounds of tiger moths, little is understood about the occurrence, function, and evolution of these sounds. We define a defense sound as an acoustic signal (air- or solid-borne vibration) produced in response to attack or threat of attack by a predator or parasitoid and that promotes survival. Defense sounds have been described in 12 insect orders, across different developmental stages, and between sexes. The mechanisms of defensive sound production include stridulation, percussion, tymbalation, tremulation, and forced air. Signal characteristics vary between species, and we discuss how morphology, the intended receiver, and specific functions of the sounds could explain this variation. Sounds can be directed at predators or non-predators, and proposed functions include startle, aposematism, jamming, and alarm, although experimental evidence for these hypotheses remains scant for many insects. The evolutionary origins of defense sounds in insects have not been rigorously investigated using phylogenetic methodology, but in most cases it is hypothesized that they evolved from incidental sounds associated with non-signaling behaviors such as flight or ventilatory movements. Compared to our understanding of visual defenses in insects, sonic defenses are poorly understood. We recommend that future investigations focus on testing hypotheses explaining the functions and evolution of these survival sounds using predator-prey experiments and comparative phylogenetics.

An Evolutionary Game Model of Sex-Dependent Antipredator Signaling

“…Thus, the net individual benefit-cost ratio of signaling is considered to be larger in males, and the evolution of signaling will be easier in males. A recent literature survey on the defensive sounds in insects by Low, Naranjo, and Yack (2021) suggested that the sex that use antipredator signals is usually males when only one sex in a species signals. A part of our finding is consistent with those in previous studies on sexual dimorphism demonstrating that the intrinsic differences between sexes brings dimorphic niches of traits, leading to the evolution of sexual dimorphism (Rice 1984;Lande 1980;Slatkin 1984).…”

Mechanism of sound production by the Chinese grasshopper Acrida cinerea (Orthoptera: Acrididae) during flight

“…The function of crepitation in most species of Acrididae has not been revealed yet. One hypothesis is that crepitation is an antipredator signal (Edmunds 1974;Low et al 2021). Another hypothesis is that crepitation is a signal to conspecifics for reproduction (Otte 1970;Elsner & Wasser 1995;Niedzlek-Feaver 1995;Berger 2008).…”

“…Sound is produced by many insects as a defense against predators (Low et al 2021). The sound produced by many species of grasshoppers when they escape by flying (Willey & Willey 1969;Otte 1970) is also considered to be an antipredator defense.…”

“…However, no empirical studies have examined the antipredator function of the sounds produced by grasshoppers during flight (e.g. startle signal or flash behavior; Edmunds 1974;Low et al 2021). An effective method used to test the antipredator function of the sound is to compare the survival rates of grasshoppers that are prevented from producing the sound with those that are permitted to produce the sound (see Corey & Hebets 2020 for the test on stridulation by the spiny orb-weaving spider).…”

Acoustic signalling in Orthoptera

“…Once a predator has been detected, orthopterans may react defensively to try and avoid being captured, such as switching to low-intensity song so only a nearby mate can hear, stopping singing completely for a time (e.g. ter Hofstede et al, 2010), and/or producing a defensive sound (a noise directed at a predator that improves the chances of survival; for a review of defensive sounds see Low et al, 2021). Haglids in the genus Cyphoderris have an unusual stridulatory method of producing a defensive sound, probably directed at ground predators, using Ander's organ (Woodrow et al, 2021).…”