Seasonal head dimorphism and taxonomy of some European species of Aprosthema (Hymenoptera: Symphyta: Argidae).

Abstract

Head shape has been regarded as an important character distinguishing species in the sterictiphorine genus Aprosthema Konow (Argidae). Oviposition experiments on southern Finnish females of A. melanurum (Klug, 1814) on Lathyrus pratensis L. (Fabaceae) showed that the overwintered female (spring generation) has a long head with temples parallel or broadening posteriorly and a shorter flagellum, whereas the female (and male) of the summer generation has a short head with strongly narrowing temples and a longer flagellum. The thick winter cocoons are in the ground. The thin soft summer cocoons are formed on the food plant or some other nearby plant, and the emerging adult does not need strong muscles to open the cocoon. A similar head shape dimorphism is found in the two generations of Aprosthema fusicorne (Thomson, 1871) feeding on Vicia cracca L. (Fabaceae), and of A. intermedium (Zaddach, 1864) = A. hyalinopterum Conde, 1934, syn. nov. feeding on Lathyrus vernus (L.) Bernh. These are the first observations of seasonal head dimorphism in sawflies. Lectotypes are designated for Hylotoma melanura Klug and Aprosthema hyalinopterum Conde. A key is presented to the 5 species of Aprosthema examined. Three species of Aprosthema are reported from England.