Abstract
Females of the parasitic wasp Nasonia vitripennis raised from the egg stage in the total absence of light but subjected to daily temperature cycles (13° to 23°C), are able to distinguish a "short-day" thermoperiod (〈 13 hours at 23°C per day) from a "long-day" thermoperiod (〈 13 hours at 23°C per day) and produce diapausing or developing progeny accordingly.