Impact of photoperiod on the sexual behavior of the black cutworm moth (Lepidoptera : Noctuidae)

We tested the hypothesis that changes in photoperiod alone are responsible fur the delay in the onset of sexual maturity that has been previously obse rved in natural populations of the migratory black cutworm, Agrotis ipsilon (Hufnagel), moth. We hypothesized that under short days, which occur at th e 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 degreesC from egg to adult under three photoregimes that they encounter in nature at dif ferent latitudes: 12:12 (L:D) h (late March and late September), li:Ib (L:D ) h, and 16:8 (L:D) h. As predicted, the mean age at which females first ca lled (i.e., released pheromone) was earlier under long-day than under short -day photoregimes, but this trend was not significant. The percentage of fe males that called over a 6-d-period a as similar among photoregimes but it varied with age. There was no interaction between photoperiod and age on th e percentage of females calling. Pheromone production, measured as the quan tity 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 ph eromone than older females. Photoperiod and age showed a significant intera ction 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 p ercentages of response than did males reared under long days. Age had a sig nificant effect on male response but it was independent from the effect of photoperiod. We conclude that although photoperiod length can influence cal ling, 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 re productive diapause that A. ipsilon undergoes in its fall migration.