Meiotic activity and the karyotype of Brachytron pratense (Müll.) (Anisoptera: Aeshnidae)

Generally, meiotic divisions occur in the odonate males almost throughout their adult life (cf. B. KIAUTA, 1978, Introduction lo insect cytotaxonomy, Nepal Research Center, Kathmandu). B. pratense, however, seems to be a remarkable exception to this rule. During a considerable number of seasons attempts have been made almost annually by the Department of Animal Cytogenetics and Cytotaxonomy, University of Utrecht to obtain the karyotype of this species, euryoecious in The Netherlands, Irom specimens collected on wings in the field. Nevertheless, the huge series of slides does not contain a single divisional stage. In a series of penultimate and ultimate instar aeshnid larvae, collected February-March, 1982 (De Uithof, Utrecht) for DNA photometric research, there was an ultimate instar male pertaining to this species. The adult emerged in the laboratory on May 10, and 13 Feulgen preparations were made about 30 hrs later. The gonial tissue appeared exceptionally active; both mitotic and meiotic divisions occurring in great numbers throughout the tissue. It seems, thus, that contrary to what is considered the general pattern of male odonate mitotic activity, in the adult B. praiense the occurrence of maturation divisions is limited to a short post-emergence period, the maturation cycle being probably completed by the time the insect takes on wings, or almost certainly so before sexual maturity has been reached. As far as I am aware, this is the first case of this phenomenon on record in the order.