Abstract

Evidence for the use of sensory modes other than olfaction in the assembly of moths is discussed. It is proposed that a multitude of sensing and signalling methods may be used. To support this hypothesis the rôle of ultrasonic emissions in Heliothis zea from the standpoint of its usefulness to the animal in communication and navigation was investigated. It was found that H. zea emits a rapidly damped 50 kc ultrasonic burst every 25 msec in synchronization with the wing beat, but not automatically produced by the wing beat. The burst is composed of two 185 μsec pulses of six oscillations each and the pulses are separated from each other by 190 μsec. Ultrasonic emissions were sporadic during the morning and afternoon hours, but became very regular in the late afternoon and evening. The effective sound pressure was greatest in the topside direction and least below. At a distance of 1·5 cm the average effective sound pressure was 98·5 dB re 0·0002 μbar. Using 0·02 μbar as the threshold for hearing in the moth, an analysis of the moth's acoustic capabilities was made. It was concluded that the ultrasonic emissions combined with the acoustic properties of the ears provided an echo-locating capability which could be used for the detection of large objects at a distance of over 2 m and the resolution of details down to 7 mm at distances up to 24 cm. Signalling for the purpose of assembling would be effective at distances of over 4 m and combined with olfactory information it should be of value in locating a mate.