Sensitivity of larvae to photoperiods controlling the adult diapause of two insects

Abstract

The sensitivity of larvae of Pyrrhocoris apterus to photoperiods controlling the adult diapause was studied by changing light conditions at various larval ages. A high proportion of adults oviposited, even when the diapause-preventing exposure of a long-day regimen (L 18, D 6) was changed 2 days before the adult ecdysis to the diapause-inducing short day (L 12, D 12). The reverse procedure resulted in all adults laying eggs. The pre-oviposition period then gradually decreased with the prolongation of the diapause-preventing treatment of larvae. The responsiveness of larvae of Leptinotarsa decemlineata was proved by keeping the adults at an intermediate photoperiod (L 14, D 10). The diapause-inducing effect of short-day conditions on the larvae was thus not reversed in adults, as occurs if the adults are exposed to the diapause-preventing long-day regimen. A general rule arises from the results. The responsiveness of larvae to the signals controlling the imaginal diapause is not excluded by oviposition of adults kept under photoperiods adverse to diapause. The effect of factors experienced by the larvae results in modification of the pre-oviposition period and of the incidence of diapause only when the adults are reared under neutral light conditions.