ABSTRACT.Daily rhythms controlling oviposition, egg‐hatching and adult eclosion in the sorghum shootfly,Atherigona soccataRondani, were investigated. Eggs were laid only during the photophase of a LD 12:12 cycle, in two peaks. Under continuous light, this oviposition was considerably attenuated but not made immediately arrhythmic. Egg‐hatching and adult eclosion both commenced just before dawn. Some feature of the scotophase during or immediately after black‐head formation apparently acts as a signal for hatching. Eclosion was controlled by light but its timing in the field was modified by temperature. The last 2–3 days of the pupal period constituted the most sensitive stage, and light signals received during this period determined the time of eclosion. Ecological advantages of these rhythms to the shootfly are di