Circa-bi-dian rhythmicity in the flight activity of the mosquito Culiseta incidens

1. 1. Circa-bi-dian (about-two-day) rhythms have been found only in the human sleep-wake cycle and in the flight activity of the mosquito Culiseta incidens. Further data on the latter are presented. 2. 2. In Culiseta, the phase relations between the circa-bi-dian activity bands and the circadian bands which precede them in each record either tend to be stable and are classifiable into four categories, or show a continuous change. 3. 3. The usefulness of this classification and the strengths and shortcomings of a two-oscillator explanation of mosquito circa-bi-dian rhythmicity are discussed.