THE AUDITORY SENSITIVITY OF ORTHOPTERA

Abstract

The author suggests that for the cricket, as for the katydid, the tympanal organ functions most effectively for the high tones, and operates alone in the range above 7,000 cycles. Unlike the katydid, however, the receptors of the foreleg are most sensitive than those of the 2d leg at the low frequencies also. This means either that the tympanal organ continues to function at the low frequencies, or that the subgenual organ of the foreleg is superior to that of the 2d leg. Of the Orthoptera examined, crickets have the poorest hearing; their upper limit extends to 15,000 or 20,000 cycles as compared with 30,000 for the grasshoppers and 60,000 or more for the katydids. The crickets have their region of greatest sensitivity at 5000 cycles, where they are able to respond to sound pressures around 0.2 dyne per sq cm, a level about 1000 times (60db) greater than that required by the human ear, in its best region around 2000 cycles. The grasshoppers show the greatest sensitivity in the region of 3000 to 5000 cycles, where their threshold is about 0.04 dyne per sq cm, about 46 db poorer than man''s at 2000 cycles. The katydids of the species Conocephalus strictus are most sensitive over the region from 10,000 to 40,000 cycles, where their threshold also is around 0.04 dyne per sq cm. The specimen of the species Neoconocephalus retusus is a little more sensitive, with a sharp peak at 15,000 cycles where the threshold also is around 0.01 dyne per sq cm, or 34 db worse than man''s at 2000 cycles.