Entrainability of circadian activity of the mosquito Culex pipiens pallens to 24-hr temperature cycles, with special reference to involvement of multiple oscillators.

Entrainability of the circadian rhythm of mosquito flight and locomotor activity was investigated by giving a 24-hr temperature cycle (28 degrees C for 16 hr, 23 degrees C for 8 hr) to the free-running rhythm or by shifting the temperature cycle. The phase angle difference between the entrained rhythm and the temperature cycle depended on the free-running period, but not on the circadian phase at which the temperature cycle started. The rhythm transients (advancing or delaying) to entrainment depended on phase, but did not depend on either the phase or the free-running period for their average speed. We postulate that flight and locomotor activity in the mosquito may be controlled by two circadian oscillators moving in different directions in response to the temperature cycle. It is likely that at least one of the oscillators is diphasic.