Ultrasonic pulse repetition rates triggering escape responses of a moth pest

The coevolutionary arms race between echolocating bats and tympanate moths has driven the evolution of ultrasound-mediated escape behaviors in moths. Bat-emitted ultrasonic pulses vary in sound intensity and temporal structure, with pulse repetition rate (PRR) which intrinsically encode critical information about predation risk, i.e., physical distance between bats and moths. However, species-specific PRR sensitivity remains underexplored, particularly in Plusiinae. This study investigates how variations in PRR modulate evasive flight and reproductive behaviors in Autographa nigrisigna (Lepidoptera: Noctuidae).

Tethered flying moths were exposed to ultrasonic stimuli (6 ms pulse duration) across 1, 5, 10, 20, 40, 80, and 160 pulses per second (= PRR). Autographa nigrisigna exhibited PRR-dependent evasive behaviors, shifting from directional turns to erratic flight and flight cessation in response to increasing ultrasonic pulse PRRs. Reproductive status modified anti-bat behavior response: unmated females showed equivalent escape responses to low predation risk (PRR10; ultrasonic pulses of echolocating bats in prey-searching mode) and high predation risk (PRR20; ultrasonic pulses in prey-chasing mode), whereas host-searching flight of gravid females were more frequently suppressed by PRR20 than PRR10. This behavioral difference may reflect adaptive trade-offs between survival and reproduction.

Mated females of A. nigrisigna selectively avoid ultrasonic pulse repetition rates reflecting a high predation risk that are emitted by predatory bats while tracking a prey. This adaptive response highlights the evolutionary balance between predator evasion and reproductive investment in nocturnal Lepidoptera. © 2025 Society of Chemical Industry.