We tested the hypothesis that changes in photoperiod alone are responsible for the delay in the onset of sexual maturity that has been previously observed in natural populations of the migratory black cutworm, Agrotis ipsilon (Hufnagel), moth.We hypothesized that under short days, which occur at the onset of the spring and fall migrations, the first age at which males and females engage in sexual communication would be later than under long days typical of nonmigratory periods. Individuals were kept at 25°C from egg to adult under three photoregimes that they encounter in nature at different latitudes: 12:12 (L:D) h (late March and late September), 14:10 (L:D) h, and 16:8 (L:D) h. As predicted, the mean age at which females first called (i. e., released pheromone) was earlier under long-day than under short-day photoregimes, but this trend was not significant. The percentage of females that called over a 6-d-period was similar among photoregimes but it varied with age. There was no interaction between photoperiod and age on the percentage of females calling. Pheromone production, measured as the quantity of Z7–12:Ac in pheromone gland extracts, was lower under long-day than under short-day photoregimes. On average, 1-d-old females produced less pheromone than older females. Photoperiod and age showed a significant interaction in their effect on the quantity of Z7–12:Ac, but not in the direction predicted by our hypothesis. Males reared under short days showed higher percentages of response than did males reared under long days. Age had a significant effect on male response but it was independent from the effect of photoperiod. We conclude that although photoperiod length can influence calling, pheromone production, and male response, it has little effect on the age at which A. ipsilon reach sexual maturity. Changes in photoperiod alone cannot explain the delayed maturity observed in the field. Other factors, alone or in combination with photoperiod, may be necessary to induce the reproductive diapause that A. ipsilon undergoes in its fall migration.
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