Photoperiodic induction of the larval diapause in the pink bollworm, Pectinophora gossypiella (Saunders)
1967
Bell, Robert Allen
The photoperiodic control of the larval diapause of the pink bollworm, Pectinophora gossypiella (Saunders) was studied in order to better understand the mechanism by which daylength controls the seasonal development of insects. The induction or prevention of diapause was found to be influenced by the action of the photoperiod on adults, eggs and all stadia of larval development. The incidence of diapausing larvae increased concomitantly with an increase in the number of exposures of eggs and larval stages to a diapause-promoting photoperiod of LD 12:12, i.e., 12 hours of light and 12 hours of dark per 24 hour cycle. However, it was possible to induce diapause in some individuals by subjecting them to inductive treatment during only the egg stage or a single larval instar. The ability of pink bollworm larvae to enter diapause was influenced by the photoperiodic conditions to which the adult parents were subjected. The greatest percentage of diapausing individuals were produced when parents were held under a long photoperiod of LD 16:8 or 14:10 with the egg and larval stages of the progeny being exposed to a short photoperiod of LD 12:12. The diapause response was decreased when the adult parents were also held in the shorter photoperiod of LD 12:12. Such results suggested that the pink bollworm possesses a dual photoperiodic response system which was referred as a "long day-short day" type. The combined action of the parental photoperiodic system and that possessed by the immature stages of the progeny apparently provide a means of detecting not only the absolute daylength but also the direction of change; that is, whether it is increasing or decreasing. The insect, then, can evidently distinguish between spring and autumn when absolute daylengths are approximately equal and physiologically prepare itself accordingly. ...
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