| heal.abstract |
The effects of 2 photoperiods, a diapause-inducing (10:14 [L:D] h) and a non-diapause inducing one (16:8 [L:D] h) at 25°C on the growth and development of larvae of the corn stalk borer, Sesamia nonagrioides, were investigated. Under a long-day photoperiod, larvae completed their development and pupated after 6 molts, whereas under a diapause-inducing short-day photoperiod, several additional molts and considerable delay of pupation were recorded. Duration of 1st to 5th instars was about the same in diapause and nondiapause destined insects, but the duration of the 6th instar was significantly longer in diapause larvae. Similarly, head capsule widths of the larvae were about the same under both photoperiods until the 5th instar. The head capsule width of all instars, under both photoperiods, is described by the logistic model. Dyar's rule, implying a geometric model, was not found appropriate for our data. Larval weights were greater under long-day photoperiod up to 5th instar, but the reverse was true for 6th instar. Only 36% of the initial number of larvae reached pupation under short-day photoperiod, whereas 74% reached pupation under long-day photoperiod. Larval mortality gradually increased, for ≈ about 150 d under short-day photoperiod, whereas under long-day photoperiod, larval mortality occurred mainly during the first few days. Mean pupal weights for diapause and nondiapause insects were 202.8 mg and 168.1 mg, respectively. Under both photoperiods, female larvae tended to pupate later and the pupae were heavier. |
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