Periodism and energy summation with special reference to flight rhythms in aphids

Summary 1. Summer populations of Aphis fabae often show a bimodal flight curve with no flight at night. 2. The teneral period between moulting and flight depends on temperature and can be estimated. 3. Increase in temperature causes the teneral period to shorten and is followed, some time later, by an increase in rate of take-off. 4. This produces the afternoon peak of flight. 5. The morning peak is usually due to aphids which, maturing overnight, accumulate and fly when rising temperature permits. 6. A graphical method is given for constructing flight curves from constant, or observed, moulting rates and the temperature during the teneral period. 7. Population periodicities in which each individual acts only once, are distinguished from individual periodicities in which the same act is repeated by the same individuals. 8. Synchronization is necessary for either type to be evident, and this may be due to rhythmic fluctuations in developmental increments preceding the act, even in short-term periodicities, rather than to behaviour responses. 9. This may apply to rhythms of flight, as in aphids, or of emergence; to seasonal periodic growth of populations in insects; or to populations of cells in regulatory organs