- University of Toronto
Summary
The auditory characteristics of two populations (laboratory reared and wild) of North American gypsy moths (Lymantriidae: Lymantria dispar L.) were sampled and the neurally derived thresholds of wild males and females to frequencies from 5 to 150 kHz compared. The noctuoid auditory receptors, A1 and A2-cell, and putative proprioceptor, B-cell, were identified. Both sexes possess neurally responsive ears but females exhibit median best frequencies significantly lower than those of males. Audiogram comparisons reveal significantly different thresholds at 5-15 kHz, 30-120 kHz and 130-140 kHz, with females less sensitive to all but the lowest frequencies. Wild male populations reveal less audiogram variability than laboratory-reared individuals, while females’ tuning curves appear more similar. The high variability present in colony moths warrants caution in the use of laboratory-reared insects for studies that assume natural levels of selection pressure. We suggest that male L.dispar possess adaptively functional ears tuned to the frequencies in the echo-location signals of bats but that the flightless females of this species are not exposed to bat predation and therefore possess ears in a state of evolutionary degeneration.
Methodology
Two independent samples of L. dispar were used in this study. Larvae were obtained from the Gypsy Moth Laboratory, United States Department of Agriculture Development Center, Otis Air Force Base, Massachusetts, and raised in our laboratories to maturity (individuals from this sample are hereafter referred to as colony moths). Wild gypsy moths were captured and analysed during July 1985 at the laboratory facilities of the Queen’s University Biology Station, Chaffey’s Lock, Ontario, Canada.