The formation of pattern on the wing of the moth,Ephestia kühniella

Abstract

Transverse bands of coloured scales are a common feature of lepidopteran wing patterns and it has been suggested that their positions are specified by a propagated ‘Determination Wave’ (Kuhn & von Englehardt), or a ‘Gradient’ of diffusible morphogen (Nijhout). We have assessed these models in an experimental study of the formation of bands in the moth, Ephestia kuhniella. The banding pattern can be altered by microcautery of the pupal wing between 1h and 48h postpupation (at 20 degrees C) and effects are of two types: Local modifications follow early (1–3h post-pupation) cautery located on or between the presumptive sites of the bands; operations more proximally or distally on the wing have no effect. Patterns consist of a loop deflecting the nearest band medially, around the site of cautery; or an isolated ring of band scales surrounding the operation site, with the two bands in their normal positions. The type of pattern formed depends only on the location of the cautery, with rings following medial cautery (midway between the bands). Global modifications follow a 36–48h cautery anywhere on the wing surface and they consist of a medial displacement of both bands. The degree of displacement is very variable (with band separation reduced to 33–87% of that on the contralateral control wing) but this does not depend on location of the cautery. Furthermore, the degree of modification does not depend on the precise age at cautery, as an equivalent range of effects is produced at 36h, at 42h and at 48h. The Determination Wave model is disproved since it explicitly assumes that the different degrees of global modification form a temporal sequence (from severe early to mild late) and they do not. Furthermore, this model cannot explain adequately the formation of loop or ring local modifications. The Gradient model can account for many features of the results, but it does not readily explain the ring local modifications or the effect of (36–48h) cautery in causing a global change in the banding pattern, independent of the site or precise time of operation.