EFFECTS OF SHORT-DAY AND LONG-DAY PHOTOPERIODS ON GROWTH AND DEVELOPMENT OF SESAMIA-NONAGRIOIDES (LEPIDOPTERA, NOCTUIDAE)

The effects of 2 photoperiods, a diapause-inducing (10:14 [L:D] h) and a nondiapause inducing one (16:8 [L:D] h) at 25 degrees C on the grow th and development of larvae of the corn stalk borer, Sesamia nonagrio ides, were investigated. Under a long-day photoperiod, larvae complete d their development and pupated after 6 molts, whereas under a diapaus e-inducing short-day photoperiod, several additional moils and conside rable delay of pupation were recorded. Duration of 1st to 5th instars was about the same in diapause and nondiapause destined insects, but t he duration of the 6th instar was significantly longer in diapause lar vae. Similarly head capsule widths of the larvae were about tile same under both photoperiods until the 5th instar. The head capsule width o f all instars, under both photoperiods, is described by the logistic m odel. Dyar's rule, implying a geometric model, was not found appropria te for our data. Larval weights were greater under long-day photoperio d up to 5th instar, but tile reverse was true for 6th instar. Only 36% of the initial number of larvae reached pupation under short-day phot operiod, whereas 74% reached pupation under long-day photoperiod. Larv al mortality gradually increased, for approximate to about 150 d under short-day photoperiod, whereas under long-day photoperiod, larval mor tality occurred mainly during the first few days. Mean pupal weights f or diapause and nondiapause insects were 202.8 mg and 168.1 mg, respec tively. Under both photoperiods, female larvae tended to pupate later and the pupae were heavier.