Making waves: the use of sound by a mosquito and three moth species

Mosquitoes hear wingbeat sounds with antennal Johnston’s organs. In males, their sensitivity is thought to be enhanced by long fibrils on the antennae; males of many species erect these fibrils before they swarm with females. I investigated the anatomy and acoustic properties of antennae of male and female Aedes togoi, a species whose males erect these long fibrils before swarming. Many moths also hear, but several species that communicate with wingbeat sound have no tympanal organs, sensitive ears thought to have evolved in moths to detect the ultrasonic echolocation of bats. I therefore investigated potential ears in three species known to use sounds, tympanate Indianmeal moths, Plodia interpunctella (IMM) and atympanate peach twig borers, Anarsia lineatella (PTB), and webbing clothes moths, Tineola bisselliella (WCM). These investigations used microscopy, laser vibrometry and electrophysiology. Male and female A. togoi antennae vibrate best at 385 and 252 Hz, respectively, males near the female wingbeat frequency (wbf) of 306 Hz; females are unlikely to hear male wbfs of 523 Hz. In contrast, both sexes of IMM had wbfs near 50 Hz, with associated synchronous ultrasonic clicks spanning 25-80 kHz. Male tympana vibrated best at 90 kHz, females at 70 kHz, whereas the antennae of both sexes vibrated best near 150 Hz, the 3rd harmonic of their wbf. Similarly, both sexes of PTB had wbfs near 56 Hz, with associated ultrasonic clicks spanning 25-80 kHz. Their antennae vibrated in response to wingbeat sound, and an air-backed circular area on the metepisternite of both sexes vibrated best at 90 kHz but did not meet all the criteria for an ear. Finally, male WCM had a wbf of 58 Hz but females never flew or fluttered. Male and female antennae vibrated in response to the wbf and had a best frequency at 100 Hz, near the 2nd harmonic of the wbf. I conclude that these moths, like mosquitoes, have mechanically resonant antennae sensitive to sounds. Like many other flies and bees, the moths may use their antennae to detect wbfs. Because they have little acoustical effect, I suggest a different function for fibrils of male mosquitoes.