Ontogenetic timing of photoperiodic sensitivity is critical in the life history of insects that rely on photoperiod as a token stimulus. The life stages of Orius insidiosus (Say) sensitive to photoperiod for diapause induction were investigated by transferring predators between short (10:14 [L:D] h) and long (14:10[L:D] h) constant photoperiods (at 20°C) at various life stages. Bugs were considered to be in diapause if their preoviposition period exceeded 14 d after adult eclosion. The first three instars exhibited no clear sensitivity to photoperiod relative to diapause induction or intensity (as measured by preoviposition period). The fourth instar was somewhat sensitive, appearing to enhance the sensitivity of subsequent stages. In contrast, the fifth instar was highly sensitive to the short photoperiod. Exposure of bugs to short photoperiods during this instar induced diapause in at least 50% of the population. Likewise, the adult stage was sensitive to photoperiod during at least the first 14 d after eclosion. Exposure to short photoperiods during the early adult stage also appears to be necessary to induce diapause in ≈50% of the population. In addition, short photoperiod served to maintain diapause in adult females. Transferring diapausing adults from short to long photoperiods accelerated diapause termination relative to those remaining in short photoperiod.
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Vol. 93 • No. 5