LIGHT AND TEMPERATURE ENTRAINMENT OF A LOCOMOTOR RHYTHM IN HONEYBEES

The circadian locomotor (walking) rhythms of forager honeybees (Apis m ellifera ligustica L.) were entrained to eight different 24 h light-da rk cycles. The phases of activity onset, peak activity, and offset wer e correlated with the lights-off transition, suggesting lights-off as the primary zeitgeber for the rhythm. Further support for this hypothe sis was provided by LD 1:23 experiments, in which entrainment occurred when the light pulse was situated at the end, but not at the beginnin g, of the subjective photophase. Steady-state entrainment of the locom otor rhythm was achieved with square-wave temperature cycles of 10-deg rees-C amplitude under constant dark: most of the activity occurred wi thin the early thermophase. Smaller amplitude temperature cycles yield ed relative coordination of the rhythm. Interactions of temperature an d light-dark cycles resulted in entrainment patterns different from th ose elicited in response to either cycle alone or those formed by a si mple combination of the two separate responses. Furthermore, temperatu re cycles having amplitudes insufficient for entrainment of the rhythm nevertheless modified the pattern of entrainment to light-dark cycles , suggesting a synergism of light and temperature effects on the under lying circadian clock system.