Bilateral Asymmetry: a Larval Polymorphism in some Argid Sawflies (Hymenoptera, Symphyta)

Abstract

BILATERAL asymmetry is virtually unknown among insects, other than as a rare aberration. Pasteels¹ has briefly noted the occurrence of colour asymmetry in larvae of Arge ustulata (L.) in Belgium and the Tyrol. Intensive collecting in south-eastern England and northwestern Scotland has shown British populations of A. fuscipes (Fallén) and A. ustulata feeding on birches (Betula pendula Roth, and B. pubescens Ehrh.) to consist of symmetrical and asymmetrical individuals. Both forms appear to be present in proportions too large to be attributable to recurrent mutation alone. Unfortunately, however, samples from particular localities have so far been too small to allow accurate frequency determinations. Nevertheless, assuming genetic control, this phenomenon, would appear to constitute a true polymorphism (Ford²).