Identification of ecdysteroidogenic enzyme genes and their expression during pupal diapause in the cabbage armyworm, Mamestra brassicae.

In this study, we identified ecdysteroidogenic enzymes in the cabbage armyworm, Mamestra brassicae, and demonstrated reduced expression of these genes during diapause. Some insects employ a temporary developmental arrest, diapause, to survive in severe environments. The titres of the moulting hormone ecdysteroid were reduced in diapause pupae of M. brassicae; therefore, ecdysteroidogenesis might be suppressed by a diapause-specific mechanism. To clarify expression changes of ecdysteroidogenic enzyme genes during diapause in M. brassicae, we first identified the genes for seven ecdysteroidogenic enzymes: Neverland, Non-molting glossy (Nm-g), CYP307A1 (Spook), CYP306A1 (Phantom), CYP302A1 (Disembodied), CYP315A1 (Shadow) and CYP314A1 (Shade). Enzymatic assays using heterologous expression in Drosophila Schneider 2 (S2) cells and analysis of mRNA distribution indicated that the identified genes were ecdysteroidogenic enzymes of M. brassicae. Expression levels of these ecdysteroidogenic enzyme genes were compared between prothoracic glands in different pupal stages throughout diapause. Immediately after pupation, diapause-destined pupae showed similar expression levels of ecdysteroidogenic enzyme genes to those of nondiapause pupae. All of these genes showed reduced gene expression after diapause initiation. Expression was immediately increased in diapause-destined pupae at the postdiapause quiescence phase. These results indicate that reduced expression of ecdysteroidogenic enzyme genes suppresses ecdysteroidogenesis and maintains developmental arrest during diapause.

Aestival dormancy in the cabbage moth Mamestra brassicae L. (Lepidoptera: Noctuidae) : 2. Geographical variation in two traits: Day length thresholds triggering aestival dormancy and duration of aestival dormancy.

In a geographically wide distribution the life cycles of different populations of the cabbage moth Mamestra brossicae are adapted to a remarkable diversity of climatic conditions. This is undoubtedly a proof of its success in adaptation. Some populations living in regions characterized by a drought period interrupting the growth season are capable of distinguishing between one critical day length signalling the onset of the drought period and another signalling the end of the growth season. This study, therefore, is primarily concerned with the geographical patterns in the variability of the adaptional responses of populations exposed to environmental conditions requiring different strategies and tactics in, synchronizing individual, life cycles. It is also a contribution to our understanding of evolutionary mechanisms maintaining median responses to photoperiodically inductive day lengths in geographically different populations. The populations investigated originated from regions differing in predictability of the incidence, onset and duration of a drought period: Freiburg (48.0°N, Southern Germany), Avignon (44.0°N, Southern France), and Argelès (42.5°N, Southern France). Geographical variation with respect to both onset and duration of a drought period consequently results in clinal variation of the variability of innate day length thresholds triggering aestival dormancy and of innate duration of aestivation. In this paper we considered the influence of geographically changing temperatures on aestival dormancy induction. Even in southern populations of M. brassicae a temperature dependent "switch off"-mechanism exists which prevents aestival dormancy under certain environmental conditions. The effective temperatures vary geographically, too. What the geographical patterns in adaptive responses really are, is discussed.