title: [The control of melanin-incorporation into the pupal color-pattern of the cabbage white pieris brassicae L.]
abstract: The pupal cuticle of the Cabbage WhitePieris brassicae L. contains a pattern of black patches, the variation of which is controlled by external factors. Their way of influence is investigated.A classification of the melanization of the pupae is based on the variation of the pattern of black patches. The patches vary in their size. In case of weak melanization some of them are absent, but they do not vary in their position and their shape, and they never exceed a certain maximum size.This means that the integument contains a pattern of areas qualified for melanin deposition into the cuticle, and external factors determine to what extent this potency is realized.To a small extent, melanization is temperature-dependent. In total darkness the strongest melanization is achieved between 25° C and 28° C. Above and below that the melanization is weaker.The most important external influence on melanization is that of the light conditions. - It determines the degree of melanization during a sensitive period after the caterpillar has stopped moving about and before it becomes a pre-pupa.The strongest melanization results on dark background in bright illumination, a somewhat weaker melanization in total darkness and the weakest melanization in illumination on light background. Probably a strong contrast between the illumination and the reflection from the ground enhances the melanization.If a red filter is applied to the illumination, the melanization is weakened; although the total intensity of light is smaller, the pupae are lighter. On the other hand, the filtering out of the long-wave range by a blue filter results in stronger melanization. This means that long-waved light suppresses melanization more than short-waved light does.In equal illumination yellow background causes a weaker melanization than white and black background. Evidently, the color of the light reflected by the ground influences the pigmentation in the same way as that of the illumination does.Melanization is influenced not only by the light acting through the eyes, but also by the light which acts on the integument of the thorax and the abdomen. This does, however, not affect the pigmentation of the integument directly, for isolated abdomina do not adapt their color to light conditions.If the body of the pre-pupa is ligatured, only that part of the body anterior to the ligature will adapt its melanization to the light conditions. The posterior parts are uniform in melanization. It is as strong as that of pupae from total darkness. It is concluded that the pigmentation is controlled by a melanization inhibiting factor, which is distributed from the anterior part of the body. - Further ligaturing experiments show that there is a critical period during which this factor is distributed through the body. This period begins while the caterpillar becomes a pre-pupa.Comparison of these results with those obtained from other Rhopalocera show that the incorporation of melanin into the cuticle is always controlled by a melanization inhibiting hormone, while the incorporation of brown pigments is influenced by pigmentation promoting hormone. Therefore, the different results in ligaturing experiments do not necessarily mean species variation in the controlling hormones, but can be explained by a different action of the same hormonal system on the formation of different pigments.
authors.affiliation: I. Zoologisches Institut der Universität Göttingen, Deutschland.
authors.forename: Alert
authors.initials: A
authors.lastname: Oltmer