Characteristics and possible function of wingbeat acoustic emissions of tortricid moths

Abstract Most moths are nocturnal flying insects and some species have evolved ears to detect bats, or produce ultrasounds to dissuade or confuse them. Normally moths emit anti-bat ultrasounds when they hear bat echolocation calls, but recently it has been shown that deaf moths emit anti-bat ultrasounds continuously from specialized structures (aeroelastic tymbals) located on their wings. Structures resembling aeroelastic tymbals have been suggested from museum specimens in the family Tortricidae, and it has been proposed that members of this family can emit anti-bat ultrasounds. We recorded the wingbeat acoustic emission of three tortricid species that are predated by bats, and found that both sexes of all three species emit brief ultrasound pulses within the bat´s hearing frequency range at specific positions of the wingbeat cycle. However, the ultrasound pulses are very quiet (ca. 20 dB SPL at 10 cm), their emission is arbitrary (not all individuals and not every wing stroke produces them), and the wings do not bear specialized sound-producing structures. This evidence suggests that the ultrasound pulses emitted by tortricid moths during wingbeat would not be useful as an anti-bat defense mechanism. Tortricids are atympanic, so these faint wingbeat ultrasounds pulses are probably not useful in intraspecific communication either.