Response characteristics of cold cell on the antenna ofLocusta migratoria L.

Summary

The dendritic outer segment of the cell which is most likely the cold unit in the poreless coeloconic sensilla onLocusta migratoria antennae, has finger-like projections up to 1.5 μm long and 0.13 μm thick (Fig. 1). This unit responds to constant temperature, to slowly changing temperature and to step changes. Under stationary conditions impulse frequency attained 35 imp/s. Between 14 °C and 41 °C the higher frequencies were associated with the higher temperatures (Fig. 5). In this range the differential sensitivity is positive but not large: + 0.8 (imp/s)/°C. Its resolving power for steady temperature is 4.7 °C.

Downward step changes produced by shifting between airstreams at different temperatures yield far higher frequencies (Figs. 2, 3). Step amplitudes were between −0.1 °C and −12 °C; the conditioning temperature from which the steps were initiated, was between 16 °C and 33 °C. Frequency peaked during the first 50 ms after stimulus onset (Fig. 2) and reached its highest values (310–340 imp/s) at initial temperatures above 30 °C and steps larger than −10 °C (Fig. 4). The mean differential sensitivity from 23 curves was −19 (imp/s)/°C and the resolving power 0.6 °C.

During slowly changing temperature the impulse frequency was governed by two parameters simultaneously: ambient temperature and its rate of change. Rates were between 0.001 °C/s or less, and 0.03 °C/s in either direction. Frequency was higher during slow cooling at a given temperature than during slow warming (Fig. 6). The average differential sensitivity to the rate of change was −210 (imp/s)/(°C/s). Further, the larger responses to cooling developed at lower ambient temperatures (differential sensitivity: −1.0 (imp/s)/°C). It is to be noted that this sign is negative, in contrast to the sign for differential sensitivity to constant temperature and also for the influence of initial temperature on the response to downward step changes.