ADAPTATION TO CHEMICAL STIMULATION OF THE TARSAL RECEPTORS OF THE BLOWFLY

Abstract

1. When receptors located in the tarsi of the blowfly Phormia regina are stimulated by solutions of sucrose, the insect responds by extending its proboscis. 2. The lowest concentration which would elicit a response from 50% of the population studied was taken as the acceptance threshold. The threshold value obtained depended upon the order in which different concentrations were offered for testing. 3. Adaptation was demonstrated by comparing threshold values obtained (1) by offering solutions in ascending series of concentrations, (2) in descending series, (3) by a random technique, (4) following exposure of the tarsi to subliminal concentrations in one case and supraliminal in the other. The process of adaptation which was measured represented predominantly a state which had been brought about at some level in the central nervous system. 4. The time required for adaptation increased as the logarithm of concentration. For sucrose it varied from one to 13 seconds. Stimulation by mixtures of glycol (unacceptable) and fructose (acceptable) resulted in adaptation to each component.