Juvenile hormone production and sexual maturation in true armyworm, Pseudaletia unipuncta (HAW.) (Lepidoptera: Noctuidae): a comparison of migratory and non-migratory populations
McNeil, J.N. | Laforge, M. | Bedard, C. | Cusson, M.
Previous work on North American populations of the true armyworm, Pseudaletia unipuncta, has shown that (1) ovarian development, pheromone synthesis, and the onset of calling (behavior associated with the emission of the sex pheromone) in virgin females are positively correlated with an increase in juvenile hormone (JH) production, and (2) sexual maturation is delayed under short-day, low-temperature conditions. Based on these results and on the observation that this insect is unable to survive the low temperatures of the Canadian winter, it has been hypothesized that armyworm moths undertake seasonal north-south migrations in response to predictable habitat deterioration. Recently we obtained material from the Azores, a volcanic archipelago in the Atlantic Ocean where the armyworm sustains populations all year round. We, therefore, undertook a comparative study to test the hypothesis that the earlier onset of calling behavior observed in this non-migrant population, relative to the North American population under identical conditions, was associated with an earlier induction of JH biosynthesis and a more rapid ovarian development. The results clearly supported this hypothesis: JH biosynthesis increased at a significantly younger age in Azorean females, although there were no differences in the relative proportions of the three JH homologues produced in vitro by CA of females sacrificed on their first night of calling. The early production of JH was reflected in a more rapid ovarian maturation although the data suggest that sexual maturation in the Azorean population may require a lower JH titer. The importance of the observed differences are discussed with respect to the presence or absence of migration in each population.
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