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Aspoeck, Horst; Abbt, Viktoria; Aspoeck, Ulrike; Gruppe, Axel 
The Phenomenon of Metathetely, formerly known as Prothetely, in Raphidioptera (Insecta: Holometabola: Neuropterida) 
For completion of their life cycle, most snakefly species require two years, some only one, and others (at least single specimens) three years or more In most species, the larvae of the final stage hibernate in a state of quiescence, pupate in spring and emerge as adults shortly thereafter. Hibernation starts when the temperature decreases, thus inducing quiescence in the larva. If the temperature decrease is withheld during the last hibernation, the larvae remain active and usually continue to molt, but will not pupate successfully in spring. Moreover, most of them will die prematurely and prior to that will often develop considerable pathomorphological alterations of the eyes, sometimes also the antennae, some develop wing pads and occasionally even pathomorphological modifications of the last abdominal segments. Until now, this phenomenon in Raphidioptera has been inaccurately referred to as ``prothetely″, however, in reality, it represents ``metathetely″. The degree and duration of lower temperatures in winter that are required for a normal pupation after hibernation have been presumed to be different among the species So far, no standardized experiments have been carried out to clarify this. Here, we report on results of chilling the final larval stage of three species - Phaeostigma (Ph.) notata (Fabricius), Raphidia (R.) mediterranea (H. Aspock, U. Aspock & Rausch), and Mongoloraphidia (M.) sororcula (H. Aspock & U. Aspock) - from +20 degrees CC to +4 degrees degrees C for 4, 8, 12, 16, and 20 weeks. As expected considerable differences between the species were found M. sororcula, which occurs in a region with markedly continental climate with a very cold winter, requires the longest period of chill for a normal metamorphosis R. mediterranea, which occurs in Mediterranean areas with only short cold periods, needs only short periods of chilling for successful development and normal pupation. Ph. notata, which is distributed in large parts of extramediterranean Europe, necessitates a distinctly greater chilling than R. mediterranea, but less than M. sororcula. At any rate, a +4 degrees C chilling for 20 weeks is sufficient to prevent metathetely in all species. Each metathetelously affected individual, even those from the same species, differs in some detail from all others Presumably, these pathomorphological alterations are the result of an unsuccessful pupation, rather than an early appearance of imaginal characters. Thus, it is appropriate to term the phenomenon ``metathetely″ rather than ``prothetely″. The physiological background of pathomorphological alterations due to withholding the chill is still entirely unknown. Various forms of metathetely in the three species are shown in 28 figures. The decrease of temperature as a precondition of pupation or - generally spoken - of normal and successful metamorphosis of snakeflies is convincingly correlated with the distribution of extant Raphidioptera in the world. 
Agulla (A.) astuta (Banks, 1911); Agulla (A.) bicolor (Albarda, 1891); Agulla (A.) bractea (Carpenter, 1936); Mongoloraphidia (M.) sororcula (H. Aspock & U.Aspock, 1966); Phaeostigma (Ph.) notata (Fabricius, 1781); Phaeostigma (Magnoraphidia) major (Burmeister, 1839); Raphidia (R.) mediterranea H. Aspock; U.Aspock & Rausch; 1977; chilling duration; development; distribution; hibernation; larvae; pathomorphology; pupation; quiescence; rearing; temperature 
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