Antennal hygroreceptors of the honey bee, Apis mellifera L.

Antennal hygroreceptors of the honey bee, Apis mellifera L., have been investigated electrophysiologically and the sensillum containing these receptors with SEM. Moist and dry hygroreceptors have been identified along with a thermal receptor in a specialized coeloconic sensillum. This sensillum comprises a cuticular, shallow depression (diameter; 4 micrometer) having a central opening (1.4-1.5 micrometer) and a mushroom-shaped protrusion (1.4-1.5 micrometer) from the opening. The head of the protrusion is irregular in shape and is not perforated. This sensillum has been thus far referred to as a "sensillum campaniformium" (Dietz and Humphreys 1971), henceforth, it is referred to as a coelocapitular sensillum. The responses of both moist and dry hygroreceptors are of a phasic-tonic manner. Both receptors are antagonistic with respect to their responses to humidity; one responds with an increase in impulse frequency to rising humidity, the other to falling humidity. The humidity-response relationship is independent of stimulus flux.