Circadian control of oviposition activity in Ostrinia nubilalis.

Oviposition activity in the European corn borer, Ostrinia nubilalis, is under circadian control. Light cycles entrain the rhythm, and the system free-runs in constant darkness (DD) with a circadian period (tau). The lability of tau is evident in the DD free runs following entrainment to various light cycles. Oviposition activity is strongly suppressed in constant light but a circadian rhythm is initiated upon transfer to DD. The phase-response curve (PRC) for 1-h light pulses is type 1, not type 0 as predicted by Beck's dual system theory. The PRC can be used to predict entrained steady states in non-24-h light cycles (T's). Predicted phase relationships between the light component of the cycle and the rhythm in T19 and T26 are in close agreement with the observed peaks of oviposition. Symmetric skeleton photoperiods (two 1-h light pulses per cycle) also entrain the rhythm to the shorter of the two alternatives that are possible in these regimes.