Deaf moths employ acoustic Müllerian mimicry against bats using wingbeat-powered tymbals

Abstract

Emitting ultrasound upon hearing an attacking bat is an effective defence strategy used by several moth taxa. Here we reveal how Yponomeuta moths acquire sophisticated acoustic protection despite being deaf themselves and hence unable to respond to bat attacks. Instead, flying Yponomeuta produce bursts of ultrasonic clicks perpetually; a striated patch in their hind wing clicks as the beating wing rotates and bends. This wing structure is strikingly similar to the thorax tymbals with which arctiine moths produce their anti-bat sounds. And indeed, Yponomeuta sounds closely mimic such arctiine signals, revealing convergence in form and function. Because both moth taxa contain noxious compounds, we conclude they are mutual Müllerian acoustic mimics. Yponomeuta’s perpetual clicking would however also attract bat predators. In response, their click amplitude is reduced and affords acoustic protection just as far as required, matching the distance over which bat biosonar would pick up Yponomeuta echoes anyway – advanced acoustic defences for a deaf moth.

Fireflies produce ultrasonic clicks during flight as a potential aposematic anti-bat signal

“…Similar clicks are produced by many insects (not necessarily by the wings) for means of communication, including many species of beetles (Alexander et al, 1963;Barbero et al, 2009;Buchler et al, 1981;Conner and Corcoran, 2012;Corcoran and Hristov, 2014;Lyal and King, 1996). Some moths even evolved sound production mechanisms to disrupt bat echolocation (Corcoran et al, 2010;Corcoran and Hristov, 2014;Dunning and Roeder, 1965;M0hl and Miller, 1976;O'Reilly et al, 2019;ter Hofstede and Ratcliffe, 2016). Although most moths do not produce wingbeat clicks in flight, some noxious moths have evolved clicking probably as an aposematic mechanism (Corcoran et al, 2010;Corcoran and Hristov, 2014;Dunning and Roeder, 1965;Hristov and Conner, 2005;M0hl and Miller, 1976;O'Reilly et al, 2019;Rydell, 1998; ter Hofstede and Ratcliffe, 2016).…”

“…(3) Finally, many moths are known to signal their noxiousness using ultrasonic clicks with similar , 2016). This includes moths that cannot hear bats, as has been recently shown (O'Reilly et al, 2019). Bats are known to avoid clicking moths (M0hl and Miller, 1976; ter Hofstede and Ratcliffe, 2016), so producing moth-like clicks (even if in a different rate) might assist fireflies to avoid predation through the act of inter-specific Mullerian mimicry.…”

“…Some moths even evolved sound production mechanisms to disrupt bat echolocation (Corcoran et al, 2010;Corcoran and Hristov, 2014;Dunning and Roeder, 1965;M0hl and Miller, 1976;O'Reilly et al, 2019;ter Hofstede and Ratcliffe, 2016). Although most moths do not produce wingbeat clicks in flight, some noxious moths have evolved clicking probably as an aposematic mechanism (Corcoran et al, 2010;Corcoran and Hristov, 2014;Dunning and Roeder, 1965;Hristov and Conner, 2005;M0hl and Miller, 1976;O'Reilly et al, 2019;Rydell, 1998; ter Hofstede and Ratcliffe, 2016). Interestingly, the firefly clicks have hardly any energy below 20 kHz.…”

Survival Sounds in Insects: Diversity, Function, and Evolution

“…These traits may aid in learning and memory retention as reported for clicker training with vertebrates (Smith and Davis, 2008). It has been reported that some moths produce ultrasonic aposematic sounds continually during flight (O'Reilly et al, 2019). Such proposed warning sounds that are always turned 'on, ' analogous to warning coloration, would be interesting to explore further with live predators.…”

“…These are located on the prothorax (#45, Figure 3A) or metathorax (#44, Figure 3A) in Lepidoptera, and on the first abdominal segment in Hemiptera (#20, Figure 3A). However, some Nymphalidae butterflies use a portion of their forewing membrane as a tymballike structure that buckles to produce clicks (#48, Figure 3A) (Møhl and Miller, 1976), and some Yponomeutidae moths use a part of their hind wing in a similar manner (#57, Figure 3A) (O'Reilly et al, 2019). Forced air mechanisms are found in both adults and juveniles.…”