Summary
The auditory characteristics of the arctiid moth, Cycnia tenera were examined using two behavioral criteria, sound production and flight cessation. The majority of the individuals tested indicated a maximum sensitivity to frequencies between 30 and 50 kHz although there is a substantial degree of interindividual variation. Spectral analyses of the echolocation/hunting cries of two species of sympatric, insectivorous bats, Eptesicus fuscus and Myotis lucifugus reveal maximally intense spectral peaks at 29.3 and 41.9 kHz, respectively. The audiograms offer a behavioral correlation to neural studies done with other species of moths and illustrate the existence of behaviorally expressed intensity discrimination in these insects. The variation evident between individuals may represent the differential response characteristics reported for free-flying tympanate moths in field conditions.
Methodology
Specimens of Cycnia tenera H/ibner were captured at ultraviolet lights located at the Queen's University Biology Station near Chaffey's Locks, Leeds County, Ontario, Canada. Cycnia tenera was chosen for the study because of its relatively slow habituation and its high level of responsiveness to acoustic stimuli. Moths were generally tested on the night of capture or were placed in vials and kept until the following night. Unanesthetized moths were manually restrained while their thoracic terga were brushed free of scales and hair in preparation for mounting. They were then attached to the head of a dissecting pin with a drop of adhesive wax (Cenco Softseal Tackiwax) in such a way as to ensure the free movement of the wings. The specimen was suspended in a normal, head-forward position 10 cm above a coated mylar, broad-field, ultrasonic speaker (McCue, 1961). Stimulus for the trials consisted of a train of 10 ms pulses delivered at a rate of 10/s produced by an Exact VCF/Sweep Signal Generator 1. The pulse train was then amplified and fed to the speaker. Trials were conducted at night under red-light conditions so as to minimize observer interference. Two forms of response (sound production and flight cessation) were used as the behavioral criteria in the tests.