Metathetely and its implications for the distribution of Raphidioptera (Insecta, Holometabola: Neuropterida)
The complete life cycle of snakeflies (order Raphidioptera) usually lasts for two years and always includes one hibernation at least. Three types of life cycles can be differentiated. In >95 % of all snakefly species the mature larva hibernates in quiescence, pupates in spring and molts two to three weeks later to the imago (Type I). If, however, decrease of temperature in winter is withheld, larvae cannot pupate successfully, but develop various pathomorphological disorders, which represent a
... which represent a form of metathetely in which they are pupae but retain many larval characters. Metathetelous pupae usually die sooner or later and can never molt to adults capable of reproduction. In experimental studies on three biogeographically different species – Raphidia (R.) mediterranea, Phaeostigma (Ph.) notata (nomenclature sensu H. Aspöck & U. Aspöck 2013a), and Mongoloraphidia (M.) sororcula – a distinct correlation between the distribution and the degree and length of chilling necessary to prevent metathetely was detected. Metathetely is apparently a determining factor for the distribution of snakeflies and a possible explanation for their lack in the south of the Northern Hemisphere as well as in the Southern Hemisphere.